Related
I'll explain by example:
Elvis Operator (?: )
The "Elvis operator" is a shortening
of Java's ternary operator. One
instance of where this is handy is for
returning a 'sensible default' value
if an expression resolves to false or
null. A simple example might look like
this:
def gender = user.male ? "male" : "female" //traditional ternary operator usage
def displayName = user.name ?: "Anonymous" //more compact Elvis operator
Safe Navigation Operator (?.)
The Safe Navigation operator is used
to avoid a NullPointerException.
Typically when you have a reference to
an object you might need to verify
that it is not null before accessing
methods or properties of the object.
To avoid this, the safe navigation
operator will simply return null
instead of throwing an exception, like
so:
def user = User.find( "admin" ) //this might be null if 'admin' does not exist
def streetName = user?.address?.street //streetName will be null if user or user.address is null - no NPE thrown
You can use the logical 'OR' operator in place of the Elvis operator:
For example displayname = user.name || "Anonymous" .
But Javascript currently doesn't have the other functionality. I'd recommend looking at CoffeeScript if you want an alternative syntax. It has some shorthand that is similar to what you are looking for.
For example The Existential Operator
zip = lottery.drawWinner?().address?.zipcode
Function shortcuts
()-> // equivalent to function(){}
Sexy function calling
func 'arg1','arg2' // equivalent to func('arg1','arg2')
There is also multiline comments and classes. Obviously you have to compile this to javascript or insert into the page as <script type='text/coffeescript>' but it adds a lot of functionality :) . Using <script type='text/coffeescript'> is really only intended for development and not production.
I think the following is equivalent to the safe navigation operator, although a bit longer:
var streetName = user && user.address && user.address.street;
streetName will then be either the value of user.address.street or undefined.
If you want it to default to something else you can combine with the above shortcut or to give:
var streetName = (user && user.address && user.address.street) || "Unknown Street";
2020 Update
JavaScript now has equivalents for both the Elvis Operator and the Safe Navigation Operator.
Safe Property Access
The optional chaining operator (?.) is currently a stage 4 ECMAScript proposal. You can use it today with Babel.
// `undefined` if either `a` or `b` are `null`/`undefined`. `a.b.c` otherwise.
const myVariable = a?.b?.c;
The logical AND operator (&&) is the "old", more-verbose way to handle this scenario.
const myVariable = a && a.b && a.b.c;
Providing a Default
The nullish coalescing operator (??) is currently a stage 4 ECMAScript proposal. You can use it today with Babel. It allows you to set a default value if the left-hand side of the operator is a nullary value (null/undefined).
const myVariable = a?.b?.c ?? 'Some other value';
// Evaluates to 'Some other value'
const myVariable2 = null ?? 'Some other value';
// Evaluates to ''
const myVariable3 = '' ?? 'Some other value';
The logical OR operator (||) is an alternative solution with slightly different behavior. It allows you to set a default value if the left-hand side of the operator is falsy. Note that the result of myVariable3 below differs from myVariable3 above.
const myVariable = a?.b?.c || 'Some other value';
// Evaluates to 'Some other value'
const myVariable2 = null || 'Some other value';
// Evaluates to 'Some other value'
const myVariable3 = '' || 'Some other value';
Javascript's logical OR operator is short-circuiting and can replace your "Elvis" operator:
var displayName = user.name || "Anonymous";
However, to my knowledge there's no equivalent to your ?. operator.
I've occasionally found the following idiom useful:
a?.b?.c
can be rewritten as:
((a||{}).b||{}).c
This takes advantage of the fact that getting unknown attributes on an object returns undefined, rather than throwing an exception as it does on null or undefined, so we replace null and undefined with an empty object before navigating.
i think lodash _.get() can help here, as in _.get(user, 'name'), and more complex tasks like _.get(o, 'a[0].b.c', 'default-value')
There is currently a draft spec:
https://github.com/tc39/proposal-optional-chaining
https://tc39.github.io/proposal-optional-chaining/
For now, though, I like to use lodash get(object, path [,defaultValue]) or dlv delve(obj, keypath)
Update (as of Dec 23, 2019):
optional chaining has moved to stage 4
For the former, you can use ||. The Javascript "logical or" operator, rather than simply returning canned true and false values, follows the rule of returning its left argument if it is true, and otherwise evaluating and returning its right argument. When you're only interested in the truth value it works out the same, but it also means that foo || bar || baz returns the leftmost one of foo, bar, or baz that contains a true value.
You won't find one that can distinguish false from null, though, and 0 and empty string are false values, so avoid using the value || default construct where value can legitimately be 0 or "".
Yes, there is! 🍾
Optional chaining is in stage 4 and this enables you to use the user?.address?.street formula.
If you can't wait the release, install #babel/plugin-proposal-optional-chaining and you can use it.
Here are my settings which works for me, or just read Nimmo's article.
// package.json
{
"name": "optional-chaining-test",
"version": "1.0.0",
"main": "index.js",
"devDependencies": {
"#babel/plugin-proposal-optional-chaining": "7.2.0",
"#babel/core": "7.2.0",
"#babel/preset-env": "^7.5.5"
}
...
}
// .babelrc
{
"presets": [
[
"#babel/preset-env",
{
"debug": true
}
]
],
"plugins": [
"#babel/plugin-proposal-optional-chaining"
]
}
// index.js
console.log(user?.address?.street); // it works
Here's a simple elvis operator equivalent:
function elvis(object, path) {
return path ? path.split('.').reduce(function (nestedObject, key) {
return nestedObject && nestedObject[key];
}, object) : object;
}
> var o = { a: { b: 2 }, c: 3 };
> elvis(o)
{ a: { b: 2 }, c: 3 }
> elvis(o, 'a');
{ b: 2 }
> elvis(o, 'a.b');
2
> elvis(o, 'x');
undefined
You can achieve roughly the same effect by saying:
var displayName = user.name || "Anonymous";
UPDATE SEP 2019
Yes, JS now supports this.
Optional chaining is coming soon to v8 read more
This is more commonly known as a null-coalescing operator. Javascript does not have one.
I have a solution for that, tailor it to your own needs, an excerpt from one of my libs:
elvisStructureSeparator: '.',
// An Elvis operator replacement. See:
// http://coffeescript.org/ --> The Existential Operator
// http://fantom.org/doc/docLang/Expressions.html#safeInvoke
//
// The fn parameter has a SPECIAL SYNTAX. E.g.
// some.structure['with a selector like this'].value transforms to
// 'some.structure.with a selector like this.value' as an fn parameter.
//
// Configurable with tulebox.elvisStructureSeparator.
//
// Usage examples:
// tulebox.elvis(scope, 'arbitrary.path.to.a.function', fnParamA, fnParamB, fnParamC);
// tulebox.elvis(this, 'currentNode.favicon.filename');
elvis: function (scope, fn) {
tulebox.dbg('tulebox.elvis(' + scope + ', ' + fn + ', args...)');
var implicitMsg = '....implicit value: undefined ';
if (arguments.length < 2) {
tulebox.dbg(implicitMsg + '(1)');
return undefined;
}
// prepare args
var args = [].slice.call(arguments, 2);
if (scope === null || fn === null || scope === undefined || fn === undefined
|| typeof fn !== 'string') {
tulebox.dbg(implicitMsg + '(2)');
return undefined;
}
// check levels
var levels = fn.split(tulebox.elvisStructureSeparator);
if (levels.length < 1) {
tulebox.dbg(implicitMsg + '(3)');
return undefined;
}
var lastLevel = scope;
for (var i = 0; i < levels.length; i++) {
if (lastLevel[levels[i]] === undefined) {
tulebox.dbg(implicitMsg + '(4)');
return undefined;
}
lastLevel = lastLevel[levels[i]];
}
// real return value
if (typeof lastLevel === 'function') {
var ret = lastLevel.apply(scope, args);
tulebox.dbg('....function value: ' + ret);
return ret;
} else {
tulebox.dbg('....direct value: ' + lastLevel);
return lastLevel;
}
},
works like a charm. Enjoy the less pain!
You could roll your own:
function resolve(objectToGetValueFrom, stringOfDotSeparatedParameters) {
var returnObject = objectToGetValueFrom,
parameters = stringOfDotSeparatedParameters.split('.'),
i,
parameter;
for (i = 0; i < parameters.length; i++) {
parameter = parameters[i];
returnObject = returnObject[parameter];
if (returnObject === undefined) {
break;
}
}
return returnObject;
};
And use it like this:
var result = resolve(obj, 'a.b.c.d');
* result is undefined if any one of a, b, c or d is undefined.
I read this article (https://www.beyondjava.net/elvis-operator-aka-safe-navigation-javascript-typescript) and modified the solution using Proxies.
function safe(obj) {
return new Proxy(obj, {
get: function(target, name) {
const result = target[name];
if (!!result) {
return (result instanceof Object)? safe(result) : result;
}
return safe.nullObj;
},
});
}
safe.nullObj = safe({});
safe.safeGet= function(obj, expression) {
let safeObj = safe(obj);
let safeResult = expression(safeObj);
if (safeResult === safe.nullObj) {
return undefined;
}
return safeResult;
}
You call it like this:
safe.safeGet(example, (x) => x.foo.woo)
The result will be undefined for an expression that encounters null or undefined along its path. You could go wild and modify the Object prototype!
Object.prototype.getSafe = function (expression) {
return safe.safeGet(this, expression);
};
example.getSafe((x) => x.foo.woo);
Jumping in very late, there's a proposal[1] for optional chaining currently at stage 2, with a babel plugin[2] available. It's not currently in any browser I am aware of.
https://github.com/tc39/proposal-optional-chaining
https://www.npmjs.com/package/#babel/plugin-proposal-optional-chaining
This was a problem for me for a long time. I had to come up with a solution that can be easily migrated once we get Elvis operator or something.
This is what I use; works for both arrays and objects
put this in tools.js file or something
// this will create the object/array if null
Object.prototype.__ = function (prop) {
if (this[prop] === undefined)
this[prop] = typeof prop == 'number' ? [] : {}
return this[prop]
};
// this will just check if object/array is null
Object.prototype._ = function (prop) {
return this[prop] === undefined ? {} : this[prop]
};
usage example:
let student = {
classes: [
'math',
'whatev'
],
scores: {
math: 9,
whatev: 20
},
loans: [
200,
{ 'hey': 'sup' },
500,
300,
8000,
3000000
]
}
// use one underscore to test
console.log(student._('classes')._(0)) // math
console.log(student._('classes')._(3)) // {}
console.log(student._('sports')._(3)._('injuries')) // {}
console.log(student._('scores')._('whatev')) // 20
console.log(student._('blabla')._('whatev')) // {}
console.log(student._('loans')._(2)) // 500
console.log(student._('loans')._(1)._('hey')) // sup
console.log(student._('loans')._(6)._('hey')) // {}
// use two underscores to create if null
student.__('loans').__(6)['test'] = 'whatev'
console.log(student.__('loans').__(6).__('test')) // whatev
well I know it makes the code a bit unreadable but it's a simple one liner solution and works great. I hope it helps someone :)
This was an interesting solution for the safe navigation operator using some mixin..
http://jsfiddle.net/avernet/npcmv/
// Assume you have the following data structure
var companies = {
orbeon: {
cfo: "Erik",
cto: "Alex"
}
};
// Extend Underscore.js
_.mixin({
// Safe navigation
attr: function(obj, name) { return obj == null ? obj : obj[name]; },
// So we can chain console.log
log: function(obj) { console.log(obj); }
});
// Shortcut, 'cause I'm lazy
var C = _(companies).chain();
// Simple case: returns Erik
C.attr("orbeon").attr("cfo").log();
// Simple case too, no CEO in Orbeon, returns undefined
C.attr("orbeon").attr("ceo").log();
// IBM unknown, but doesn't lead to an error, returns undefined
C.attr("ibm").attr("ceo").log();
I created a package that makes this a lot easier to use.
NPM jsdig
Github jsdig
You can handle simple things like and object:
const world = {
locations: {
europe: 'Munich',
usa: 'Indianapolis'
}
};
world.dig('locations', 'usa');
// => 'Indianapolis'
world.dig('locations', 'asia', 'japan');
// => 'null'
or a little more complicated:
const germany = () => 'germany';
const world = [0, 1, { location: { europe: germany } }, 3];
world.dig(2, 'location', 'europe') === germany;
world.dig(2, 'location', 'europe')() === 'germany';
?? would work in js which is equivalent to ?: in kotlin
Personally i use
function e(e,expr){try{return eval(expr);}catch(e){return null;}};
and for example safe get:
var a = e(obj,'e.x.y.z.searchedField');
I have an object like this
const obj = [{a: 'a'}];
I can get it like:
const { a } = obj[0]; //a
but what if obj['x'] doesn't exist?
I tried this with optional chainning but doesn't seem to work.
const { a } = obj?.[1];
You are close to it. You should make sure to fallback with an empty object, for the destructing later to make sense
const obj = [{a: 'a'}];
const { a } = obj?.[1] || {};
console.log(a)
Update
This would be even shorter if you don't use destructing in this case
const obj = [{a: 'a'}];
const a = obj?.[1]?.a; // or: obj?.[1]?.['a']
console.log(a)
You can use the Logical OR operator.
const { a } = obj[x] || {}
If obj does not have a property x, a will be set to undefined.
You could festructure with an index as computed property and a default object for a missing item of the array.
const
obj = [{ a: 'a' }],
{ [2]: { a } = {} } = obj;
console.log(a);
Take a look at the following three cases, where I've used optional chaining.
You need to first check if the first element of the array (index 0) exists and then check if there's a field a in it.
// Case 1:
const obj1 = [{ a: "a" }];
console.log(obj1?.[0]?.a); // "a"
// Case 2:
const obj2 = [{ b: "b" }];
console.log(obj2?.[0]?.a); // undefined
// Case 3:
const obj3 = [];
console.log(obj3?.[0]?.a); // undefined
Given a JavaScript object,
var obj = { a: { b: '1', c: '2' } }
and a string
"a.b"
how can I convert the string to dot notation so I can go
var val = obj.a.b
If the string was just 'a', I could use obj[a]. But this is more complex. I imagine there is some straightforward method, but it escapes me at present.
recent note: While I'm flattered that this answer has gotten many upvotes, I am also somewhat horrified. If one needs to convert dot-notation strings like "x.a.b.c" into references, it could (maybe) be a sign that there is something very wrong going on (unless maybe you're performing some strange deserialization).
That is to say, novices who find their way to this answer must ask themselves the question "why am I doing this?"
It is of course generally fine to do this if your use case is small and you will not run into performance issues, AND you won't need to build upon your abstraction to make it more complicated later. In fact, if this will reduce code complexity and keep things simple, you should probably go ahead and do what OP is asking for. However, if that's not the case, consider if any of these apply:
case 1: As the primary method of working with your data (e.g. as your app's default form of passing objects around and dereferencing them). Like asking "how can I look up a function or variable name from a string".
This is bad programming practice (unnecessary metaprogramming specifically, and kind of violates function side-effect-free coding style, and will have performance hits). Novices who find themselves in this case, should instead consider working with array representations, e.g. ['x','a','b','c'], or even something more direct/simple/straightforward if possible: like not losing track of the references themselves in the first place (most ideal if it's only client-side or only server-side), etc. (A pre-existing unique id would be inelegant to add, but could be used if the spec otherwise requires its existence regardless.)
case 2: Working with serialized data, or data that will be displayed to the user. Like using a date as a string "1999-12-30" rather than a Date object (which can cause timezone bugs or added serialization complexity if not careful). Or you know what you're doing.
This is maybe fine. Be careful that there are no dot strings "." in your sanitized input fragments.
If you find yourself using this answer all the time and converting back and forth between string and array, you may be in the bad case, and should consider an alternative.
Here's an elegant one-liner that's 10x shorter than the other solutions:
function index(obj,i) {return obj[i]}
'a.b.etc'.split('.').reduce(index, obj)
[edit] Or in ECMAScript 6:
'a.b.etc'.split('.').reduce((o,i)=> o[i], obj)
(Not that I think eval always bad like others suggest it is (though it usually is), nevertheless those people will be pleased that this method doesn't use eval. The above will find obj.a.b.etc given obj and the string "a.b.etc".)
In response to those who still are afraid of using reduce despite it being in the ECMA-262 standard (5th edition), here is a two-line recursive implementation:
function multiIndex(obj,is) { // obj,['1','2','3'] -> ((obj['1'])['2'])['3']
return is.length ? multiIndex(obj[is[0]],is.slice(1)) : obj
}
function pathIndex(obj,is) { // obj,'1.2.3' -> multiIndex(obj,['1','2','3'])
return multiIndex(obj,is.split('.'))
}
pathIndex('a.b.etc')
Depending on the optimizations the JS compiler is doing, you may want to make sure any nested functions are not re-defined on every call via the usual methods (placing them in a closure, object, or global namespace).
edit:
To answer an interesting question in the comments:
how would you turn this into a setter as well? Not only returning the values by path, but also setting them if a new value is sent into the function? – Swader Jun 28 at 21:42
(sidenote: sadly can't return an object with a Setter, as that would violate the calling convention; commenter seems to instead be referring to a general setter-style function with side-effects like index(obj,"a.b.etc", value) doing obj.a.b.etc = value.)
The reduce style is not really suitable to that, but we can modify the recursive implementation:
function index(obj,is, value) {
if (typeof is == 'string')
return index(obj,is.split('.'), value);
else if (is.length==1 && value!==undefined)
return obj[is[0]] = value;
else if (is.length==0)
return obj;
else
return index(obj[is[0]],is.slice(1), value);
}
Demo:
> obj = {a:{b:{etc:5}}}
> index(obj,'a.b.etc')
5
> index(obj,['a','b','etc']) #works with both strings and lists
5
> index(obj,'a.b.etc', 123) #setter-mode - third argument (possibly poor form)
123
> index(obj,'a.b.etc')
123
...though personally I'd recommend making a separate function setIndex(...). I would like to end on a side-note that the original poser of the question could (should?) be working with arrays of indices (which they can get from .split), rather than strings; though there's usually nothing wrong with a convenience function.
A commenter asked:
what about arrays? something like "a.b[4].c.d[1][2][3]" ? –AlexS
Javascript is a very weird language; in general objects can only have strings as their property keys, so for example if x was a generic object like x={}, then x[1] would become x["1"]... you read that right... yup...
Javascript Arrays (which are themselves instances of Object) specifically encourage integer keys, even though you could do something like x=[]; x["puppy"]=5;.
But in general (and there are exceptions), x["somestring"]===x.somestring (when it's allowed; you can't do x.123).
(Keep in mind that whatever JS compiler you're using might choose, maybe, to compile these down to saner representations if it can prove it would not violate the spec.)
So the answer to your question would depend on whether you're assuming those objects only accept integers (due to a restriction in your problem domain), or not. Let's assume not. Then a valid expression is a concatenation of a base identifier plus some .identifiers plus some ["stringindex"]s.
Let us ignore for a moment that we can of course do other things legitimately in the grammar like identifier[0xFA7C25DD].asdf[f(4)?.[5]+k][false][null][undefined][NaN]; integers are not (that) 'special'.
Commenter's statement would then be equivalent to a["b"][4]["c"]["d"][1][2][3], though we should probably also support a.b["c\"validjsstringliteral"][3]. You'd have to check the ecmascript grammar section on string literals to see how to parse a valid string literal. Technically you'd also want to check (unlike in my first answer) that a is a valid javascript identifier.
A simple answer to your question though, if your strings don't contain commas or brackets, would be just be to match length 1+ sequences of characters not in the set , or [ or ]:
> "abc[4].c.def[1][2][\"gh\"]".match(/[^\]\[.]+/g)
// ^^^ ^ ^ ^^^ ^ ^ ^^^^^
["abc", "4", "c", "def", "1", "2", ""gh""]
If your strings don't contain escape characters or " characters, and because IdentifierNames are a sublanguage of StringLiterals (I think???) you could first convert your dots to []:
> var R=[], demoString="abc[4].c.def[1][2][\"gh\"]";
> for(var match,matcher=/^([^\.\[]+)|\.([^\.\[]+)|\["([^"]+)"\]|\[(\d+)\]/g;
match=matcher.exec(demoString); ) {
R.push(Array.from(match).slice(1).filter(x=> x!==undefined)[0]);
// extremely bad code because js regexes are weird, don't use this
}
> R
["abc", "4", "c", "def", "1", "2", "gh"]
Of course, always be careful and never trust your data. Some bad ways to do this that might work for some use cases also include:
// hackish/wrongish; preprocess your string into "a.b.4.c.d.1.2.3", e.g.:
> yourstring.replace(/]/g,"").replace(/\[/g,".").split(".")
"a.b.4.c.d.1.2.3" //use code from before
Special 2018 edit:
Let's go full-circle and do the most inefficient, horribly-overmetaprogrammed solution we can come up with... in the interest of syntactical purityhamfistery. With ES6 Proxy objects!... Let's also define some properties which (imho are fine and wonderful but) may break improperly-written libraries. You should perhaps be wary of using this if you care about performance, sanity (yours or others'), your job, etc.
// [1,2,3][-1]==3 (or just use .slice(-1)[0])
if (![1][-1])
Object.defineProperty(Array.prototype, -1, {get() {return this[this.length-1]}}); //credit to caub
// WARNING: THIS XTREME™ RADICAL METHOD IS VERY INEFFICIENT,
// ESPECIALLY IF INDEXING INTO MULTIPLE OBJECTS,
// because you are constantly creating wrapper objects on-the-fly and,
// even worse, going through Proxy i.e. runtime ~reflection, which prevents
// compiler optimization
// Proxy handler to override obj[*]/obj.* and obj[*]=...
var hyperIndexProxyHandler = {
get: function(obj,key, proxy) {
return key.split('.').reduce((o,i)=> o[i], obj);
},
set: function(obj,key,value, proxy) {
var keys = key.split('.');
var beforeLast = keys.slice(0,-1).reduce((o,i)=> o[i], obj);
beforeLast[keys[-1]] = value;
},
has: function(obj,key) {
//etc
}
};
function hyperIndexOf(target) {
return new Proxy(target, hyperIndexProxyHandler);
}
Demo:
var obj = {a:{b:{c:1, d:2}}};
console.log("obj is:", JSON.stringify(obj));
var objHyper = hyperIndexOf(obj);
console.log("(proxy override get) objHyper['a.b.c'] is:", objHyper['a.b.c']);
objHyper['a.b.c'] = 3;
console.log("(proxy override set) objHyper['a.b.c']=3, now obj is:", JSON.stringify(obj));
console.log("(behind the scenes) objHyper is:", objHyper);
if (!({}).H)
Object.defineProperties(Object.prototype, {
H: {
get: function() {
return hyperIndexOf(this); // TODO:cache as a non-enumerable property for efficiency?
}
}
});
console.log("(shortcut) obj.H['a.b.c']=4");
obj.H['a.b.c'] = 4;
console.log("(shortcut) obj.H['a.b.c'] is obj['a']['b']['c'] is", obj.H['a.b.c']);
Output:
obj is: {"a":{"b":{"c":1,"d":2}}}
(proxy override get) objHyper['a.b.c'] is: 1
(proxy override set) objHyper['a.b.c']=3, now obj is: {"a":{"b":{"c":3,"d":2}}}
(behind the scenes) objHyper is: Proxy {a: {…}}
(shortcut) obj.H['a.b.c']=4
(shortcut) obj.H['a.b.c'] is obj['a']['b']['c'] is: 4
inefficient idea: You can modify the above to dispatch based on the input argument; either use the .match(/[^\]\[.]+/g) method to support obj['keys'].like[3]['this'], or if instanceof Array, then just accept an Array as input like keys = ['a','b','c']; obj.H[keys].
Per suggestion that maybe you want to handle undefined indices in a 'softer' NaN-style manner (e.g. index({a:{b:{c:...}}}, 'a.x.c') return undefined rather than uncaught TypeError)...:
This makes sense from the perspective of "we should return undefined rather than throw an error" in the 1-dimensional index situation ({})['e.g.']==undefined, so "we should return undefined rather than throw an error" in the N-dimensional situation.
This does not make sense from the perspective that we are doing x['a']['x']['c'], which would fail with a TypeError in the above example.
That said, you'd make this work by replacing your reducing function with either:
(o,i)=> o===undefined?undefined:o[i], or
(o,i)=> (o||{})[i].
(You can make this more efficient by using a for loop and breaking/returning whenever the subresult you'd next index into is undefined, or using a try-catch if you expect such failures to be sufficiently rare.)
If you can use Lodash, there is a function, which does exactly that:
_.get(object, path, [defaultValue])
var val = _.get(obj, "a.b");
You could use lodash.get
After installing (npm i lodash.get), use it like this:
const get = require('lodash.get');
const myObj = {
user: {
firstName: 'Stacky',
lastName: 'Overflowy',
list: ['zero', 'one', 'two']
},
id: 123
};
console.log(get(myObj, 'user.firstName')); // outputs Stacky
console.log(get(myObj, 'id')); // outputs 123
console.log(get(myObj, 'user.list[1]')); // outputs one
// You can also update values
get(myObj, 'user').firstName = 'John';
A little more involved example with recursion.
function recompose(obj, string) {
var parts = string.split('.');
var newObj = obj[parts[0]];
if (parts[1]) {
parts.splice(0, 1);
var newString = parts.join('.');
return recompose(newObj, newString);
}
return newObj;
}
var obj = { a: { b: '1', c: '2', d:{a:{b:'blah'}}}};
console.log(recompose(obj, 'a.d.a.b')); //blah
2021
You don't need to pull in another dependency every time you wish for new capabilities in your program. Modern JS is very capable and the optional-chaining operator ?. is now widely supported and makes this kind of task easy as heck.
With a single line of code we can write get that takes an input object, t and string path. It works for object and arrays of any nesting level -
const get = (t, path) =>
path.split(".").reduce((r, k) => r?.[k], t)
const mydata =
{ a: { b: [ 0, { c: { d: [ "hello", "world" ] } } ] } }
console.log(get(mydata, "a.b.1.c.d.0"))
console.log(get(mydata, "a.b.1.c.d.1"))
console.log(get(mydata, "a.b.x.y.z"))
"hello"
"world"
undefined
I suggest to split the path and iterate it and reduce the object you have. This proposal works with a default value for missing properties.
const getValue = (object, keys) => keys.split('.').reduce((o, k) => (o || {})[k], object);
console.log(getValue({ a: { b: '1', c: '2' } }, 'a.b'));
console.log(getValue({ a: { b: '1', c: '2' } }, 'foo.bar.baz'));
Many years since the original post.
Now there is a great library called 'object-path'.
https://github.com/mariocasciaro/object-path
Available on NPM and BOWER
https://www.npmjs.com/package/object-path
It's as easy as:
objectPath.get(obj, "a.c.1"); //returns "f"
objectPath.set(obj, "a.j.0.f", "m");
And works for deeply nested properties and arrays.
If you expect to dereference the same path many times, building a function for each dot notation path actually has the best performance by far (expanding on the perf tests James Wilkins linked to in comments above).
var path = 'a.b.x';
var getter = new Function("obj", "return obj." + path + ";");
getter(obj);
Using the Function constructor has some of the same drawbacks as eval() in terms of security and worst-case performance, but IMO it's a badly underused tool for cases where you need a combination of extreme dynamism and high performance. I use this methodology to build array filter functions and call them inside an AngularJS digest loop. My profiles consistently show the array.filter() step taking less than 1ms to dereference and filter about 2000 complex objects, using dynamically-defined paths 3-4 levels deep.
A similar methodology could be used to create setter functions, of course:
var setter = new Function("obj", "newval", "obj." + path + " = newval;");
setter(obj, "some new val");
Other proposals are a little cryptic, so I thought I'd contribute:
Object.prop = function(obj, prop, val){
var props = prop.split('.')
, final = props.pop(), p
while(p = props.shift()){
if (typeof obj[p] === 'undefined')
return undefined;
obj = obj[p]
}
return val ? (obj[final] = val) : obj[final]
}
var obj = { a: { b: '1', c: '2' } }
// get
console.log(Object.prop(obj, 'a.c')) // -> 2
// set
Object.prop(obj, 'a.c', function(){})
console.log(obj) // -> { a: { b: '1', c: [Function] } }
var a = { b: { c: 9 } };
function value(layer, path, value) {
var i = 0,
path = path.split('.');
for (; i < path.length; i++)
if (value != null && i + 1 === path.length)
layer[path[i]] = value;
layer = layer[path[i]];
return layer;
};
value(a, 'b.c'); // 9
value(a, 'b.c', 4);
value(a, 'b.c'); // 4
This is a lot of code when compared to the much simpler eval way of doing it, but like Simon Willison says, you should never use eval.
Also, JSFiddle.
You can use the library available at npm, which simplifies this process. https://www.npmjs.com/package/dot-object
var dot = require('dot-object');
var obj = {
some: {
nested: {
value: 'Hi there!'
}
}
};
var val = dot.pick('some.nested.value', obj);
console.log(val);
// Result: Hi there!
Note if you're already using Lodash you can use the property or get functions:
var obj = { a: { b: '1', c: '2' } };
_.property('a.b')(obj); // => 1
_.get(obj, 'a.b'); // => 1
Underscore.js also has a property function, but it doesn't support dot notation.
I have extended the elegant answer by ninjagecko so that the function handles both dotted and/or array style references, and so that an empty string causes the parent object to be returned.
Here you go:
string_to_ref = function (object, reference) {
function arr_deref(o, ref, i) { return !ref ? o : (o[ref.slice(0, i ? -1 : ref.length)]) }
function dot_deref(o, ref) { return ref.split('[').reduce(arr_deref, o); }
return !reference ? object : reference.split('.').reduce(dot_deref, object);
};
See my working jsFiddle example here: http://jsfiddle.net/sc0ttyd/q7zyd/
You can obtain value of an object member by dot notation with a single line of code:
new Function('_', 'return _.' + path)(obj);
In you case:
var obj = { a: { b: '1', c: '2' } }
var val = new Function('_', 'return _.a.b')(obj);
To make it simple you may write a function like this:
function objGet(obj, path){
return new Function('_', 'return _.' + path)(obj);
}
Explanation:
The Function constructor creates a new Function object. In JavaScript every function is actually a Function object. Syntax to create a function explicitly with Function constructor is:
new Function ([arg1[, arg2[, ...argN]],] functionBody)
where arguments(arg1 to argN) must be a string that corresponds to a valid javaScript identifier and functionBody is a string containing the javaScript statements comprising the function definition.
In our case we take the advantage of string function body to retrieve object member with dot notation.
Hope it helps.
var find = function(root, path) {
var segments = path.split('.'),
cursor = root,
target;
for (var i = 0; i < segments.length; ++i) {
target = cursor[segments[i]];
if (typeof target == "undefined") return void 0;
cursor = target;
}
return cursor;
};
var obj = { a: { b: '1', c: '2' } }
find(obj, "a.b"); // 1
var set = function (root, path, value) {
var segments = path.split('.'),
cursor = root,
target;
for (var i = 0; i < segments.length - 1; ++i) {
cursor = cursor[segments[i]] || { };
}
cursor[segments[segments.length - 1]] = value;
};
set(obj, "a.k", function () { console.log("hello world"); });
find(obj, "a.k")(); // hello world
Use this function:
function dotToObject(data) {
function index(parent, key, value) {
const [mainKey, ...children] = key.split(".");
parent[mainKey] = parent[mainKey] || {};
if (children.length === 1) {
parent[mainKey][children[0]] = value;
} else {
index(parent[mainKey], children.join("."), value);
}
}
const result = Object.entries(data).reduce((acc, [key, value]) => {
if (key.includes(".")) {
index(acc, key, value);
} else {
acc[key] = value;
}
return acc;
}, {});
return result;
}
module.exports = { dotToObject };
Ex:
const user = {
id: 1,
name: 'My name',
'address.zipCode': '123',
'address.name': 'Some name',
'address.something.id': 1,
}
const mappedUser = dotToObject(user)
console.log(JSON.stringify(mappedUser, null, 2))
Output:
{
"id": 1,
"name": "My name",
"address": {
"zipCode": "123",
"name": "Some name",
"something": {
"id": 1
}
}
}
using Array Reduce function will get/set based on path provided.
I tested it with a.b.c and a.b.2.c {a:{b:[0,1,{c:7}]}} and its works for both getting key or mutating object to set value
function setOrGet(obj, path=[], newValue){
const l = typeof path === 'string' ? path.split('.') : path;
return l.reduce((carry,item, idx)=>{
const leaf = carry[item];
// is this last item in path ? cool lets set/get value
if( l.length-idx===1) {
// mutate object if newValue is set;
carry[item] = newValue===undefined ? leaf : newValue;
// return value if its a get/object if it was a set
return newValue===undefined ? leaf : obj ;
}
carry[item] = leaf || {}; // mutate if key not an object;
return carry[item]; // return object ref: to continue reduction;
}, obj)
}
console.log(
setOrGet({a: {b:1}},'a.b') === 1 ||
'Test Case: Direct read failed'
)
console.log(
setOrGet({a: {b:1}},'a.c',22).a.c===22 ||
'Test Case: Direct set failed'
)
console.log(
setOrGet({a: {b:[1,2]}},'a.b.1',22).a.b[1]===22 ||
'Test Case: Direct set on array failed'
)
console.log(
setOrGet({a: {b:{c: {e:1} }}},'a.b.c.e',22).a.b.c. e===22 ||
'Test Case: deep get failed'
)
// failed !. Thats your homework :)
console.log(
setOrGet({a: {b:{c: {e:[1,2,3,4,5]} }}},'a.b.c.e.3 ',22)
)
my personal recommendation.
do not use such a thing unless there is no other way!
i saw many examples people use it for translations for example from json; so you see function like locale('app.homepage.welcome') . this is just bad. if you already have data in an object/json; and you know path.. then just use it directly example locale().app.homepage.welcome by changing you function to return object you get typesafe, with autocomplete, less prone to typo's ..
I copied the following from Ricardo Tomasi's answer and modified to also create sub-objects that don't yet exist as necessary. It's a little less efficient (more ifs and creating of empty objects), but should be pretty good.
Also, it'll allow us to do Object.prop(obj, 'a.b', false) where we couldn't before. Unfortunately, it still won't let us assign undefined...Not sure how to go about that one yet.
/**
* Object.prop()
*
* Allows dot-notation access to object properties for both getting and setting.
*
* #param {Object} obj The object we're getting from or setting
* #param {string} prop The dot-notated string defining the property location
* #param {mixed} val For setting only; the value to set
*/
Object.prop = function(obj, prop, val){
var props = prop.split('.'),
final = props.pop(),
p;
for (var i = 0; i < props.length; i++) {
p = props[i];
if (typeof obj[p] === 'undefined') {
// If we're setting
if (typeof val !== 'undefined') {
// If we're not at the end of the props, keep adding new empty objects
if (i != props.length)
obj[p] = {};
}
else
return undefined;
}
obj = obj[p]
}
return typeof val !== "undefined" ? (obj[final] = val) : obj[final]
}
Few years later, I found this that handles scope and array. e.g. a['b']["c"].d.etc
function getScopedObj(scope, str) {
let obj=scope, arr;
try {
arr = str.split(/[\[\]\.]/) // split by [,],.
.filter(el => el) // filter out empty one
.map(el => el.replace(/^['"]+|['"]+$/g, '')); // remove string quotation
arr.forEach(el => obj = obj[el])
} catch(e) {
obj = undefined;
}
return obj;
}
window.a = {b: {c: {d: {etc: 'success'}}}}
getScopedObj(window, `a.b.c.d.etc`) // success
getScopedObj(window, `a['b']["c"].d.etc`) // success
getScopedObj(window, `a['INVALID']["c"].d.etc`) // undefined
If you wish to convert any object that contains dot notation keys into an arrayed version of those keys you can use this.
This will convert something like
{
name: 'Andy',
brothers.0: 'Bob'
brothers.1: 'Steve'
brothers.2: 'Jack'
sisters.0: 'Sally'
}
to
{
name: 'Andy',
brothers: ['Bob', 'Steve', 'Jack']
sisters: ['Sally']
}
convertDotNotationToArray(objectWithDotNotation) {
Object.entries(objectWithDotNotation).forEach(([key, val]) => {
// Is the key of dot notation
if (key.includes('.')) {
const [name, index] = key.split('.');
// If you have not created an array version, create one
if (!objectWithDotNotation[name]) {
objectWithDotNotation[name] = new Array();
}
// Save the value in the newly created array at the specific index
objectWithDotNotation[name][index] = val;
// Delete the current dot notation key val
delete objectWithDotNotation[key];
}
});
}
If you want to convert a string dot notation into an object, I've made a handy little helper than can turn a string like a.b.c.d with a value of e with dotPathToObject("a.b.c.d", "value") returning this:
{
"a": {
"b": {
"c": {
"d": "value"
}
}
}
}
https://gist.github.com/ahallora/9731d73efb15bd3d3db647efa3389c12
Solution:
function deepFind(key, data){
return key.split('.').reduce((ob,i)=> ob?.[i], data)
}
Usage:
const obj = {
company: "Pet Shop",
person: {
name: "John"
},
animal: {
name: "Lucky"
}
}
const company = deepFind("company", obj)
const personName = deepFind("person.name", obj)
const animalName = deepFind("animal.name", obj)
Here is my implementation
Implementation 1
Object.prototype.access = function() {
var ele = this[arguments[0]];
if(arguments.length === 1) return ele;
return ele.access.apply(ele, [].slice.call(arguments, 1));
}
Implementation 2 (using array reduce instead of slice)
Object.prototype.access = function() {
var self = this;
return [].reduce.call(arguments,function(prev,cur) {
return prev[cur];
}, self);
}
Examples:
var myobj = {'a':{'b':{'c':{'d':'abcd','e':[11,22,33]}}}};
myobj.access('a','b','c'); // returns: {'d':'abcd', e:[0,1,2,3]}
myobj.a.b.access('c','d'); // returns: 'abcd'
myobj.access('a','b','c','e',0); // returns: 11
it can also handle objects inside arrays as for
var myobj2 = {'a': {'b':[{'c':'ab0c'},{'d':'ab1d'}]}}
myobj2.access('a','b','1','d'); // returns: 'ab1d'
I used this code in my project
const getValue = (obj, arrPath) => (
arrPath.reduce((x, y) => {
if (y in x) return x[y]
return {}
}, obj)
)
Usage:
const obj = { id: { user: { local: 104 } } }
const path = [ 'id', 'user', 'local' ]
getValue(obj, path) // return 104
Using object-scan seems a bit overkill, but you can simply do
// const objectScan = require('object-scan');
const get = (obj, p) => objectScan([p], { abort: true, rtn: 'value' })(obj);
const obj = { a: { b: '1', c: '2' } };
console.log(get(obj, 'a.b'));
// => 1
console.log(get(obj, '*.c'));
// => 2
.as-console-wrapper {max-height: 100% !important; top: 0}
<script src="https://bundle.run/object-scan#13.7.1"></script>
Disclaimer: I'm the author of object-scan
There are a lot more advanced examples in the readme.
This is one of those cases, where you ask 10 developers and you get 10 answers.
Below is my [simplified] solution for OP, using dynamic programming.
The idea is that you would pass an existing DTO object that you wish to UPDATE. This makes the method most useful in the case where you have a form with several input elements having name attributes set with dot (fluent) syntax.
Example use:
<input type="text" name="person.contact.firstName" />
Code snippet:
const setFluently = (obj, path, value) => {
if (typeof path === "string") {
return setFluently(obj, path.split("."), value);
}
if (path.length <= 1) {
obj[path[0]] = value;
return obj;
}
const key = path[0];
obj[key] = setFluently(obj[key] ? obj[key] : {}, path.slice(1), value);
return obj;
};
const origObj = {
a: {
b: "1",
c: "2"
}
};
setFluently(origObj, "a.b", "3");
setFluently(origObj, "a.c", "4");
console.log(JSON.stringify(origObj, null, 3));
function at(obj, path, val = undefined) {
// If path is an Array,
if (Array.isArray(path)) {
// it returns the mapped array for each result of the path
return path.map((path) => at(obj, path, val));
}
// Uniting several RegExps into one
const rx = new RegExp(
[
/(?:^(?:\.\s*)?([_a-zA-Z][_a-zA-Z0-9]*))/,
/(?:^\[\s*(\d+)\s*\])/,
/(?:^\[\s*'([^']*(?:\\'[^']*)*)'\s*\])/,
/(?:^\[\s*"([^"]*(?:\\"[^"]*)*)"\s*\])/,
/(?:^\[\s*`([^`]*(?:\\`[^`]*)*)`\s*\])/,
]
.map((r) => r.source)
.join("|")
);
let rm;
while (rm = rx.exec(path.trim())) {
// Matched resource
let [rf, rp] = rm.filter(Boolean);
// If no one matches found,
if (!rm[1] && !rm[2]) {
// it will replace escape-chars
rp = rp.replace(/\\(.)/g, "$1");
}
// If the new value is set,
if ("undefined" != typeof val && path.length == rf.length) {
// assign a value to the object property and return it
return (obj[rp] = val);
}
// Going one step deeper
obj = obj[rp];
// Removing a step from the path
path = path.substr(rf.length).trim();
}
if (path) {
throw new SyntaxError();
}
return obj;
}
// Test object schema
let o = { a: { b: [ [ { c: { d: { '"e"': { f: { g: "xxx" } } } } } ] ] } };
// Print source object
console.log(JSON.stringify(o));
// Set value
console.log(at(o, '.a["b"][0][0].c[`d`]["\\"e\\""][\'f\']["g"]', "zzz"));
// Get value
console.log(at(o, '.a["b"][0][0].c[`d`]["\\"e\\""][\'f\']["g"]'));
// Print result object
console.log(JSON.stringify(o));
Here is my code without using eval. It’s easy to understand too.
function value(obj, props) {
if (!props)
return obj;
var propsArr = props.split('.');
var prop = propsArr.splice(0, 1);
return value(obj[prop], propsArr.join('.'));
}
var obj = { a: { b: '1', c: '2', d:{a:{b:'blah'}}}};
console.log(value(obj, 'a.d.a.b')); // Returns blah
Yes, extending base prototypes is not usually good idea but, if you keep all extensions in one place, they might be useful.
So, here is my way to do this.
Object.defineProperty(Object.prototype, "getNestedProperty", {
value : function (propertyName) {
var result = this;
var arr = propertyName.split(".");
while (arr.length && result) {
result = result[arr.shift()];
}
return result;
},
enumerable: false
});
Now you will be able to get nested property everywhere without importing module with function or copy/pasting function.
Example:
{a:{b:11}}.getNestedProperty('a.b'); // Returns 11
The Next.js extension broke Mongoose in my project. Also I've read that it might break jQuery. So, never do it in the Next.js way:
Object.prototype.getNestedProperty = function (propertyName) {
var result = this;
var arr = propertyName.split(".");
while (arr.length && result) {
result = result[arr.shift()];
}
return result;
};
This is my extended solution proposed by ninjagecko.
For me, simple string notation was not enough, so the below version supports things like:
index(obj, 'data.accounts[0].address[0].postcode');
/**
* Get object by index
* #supported
* - arrays supported
* - array indexes supported
* #not-supported
* - multiple arrays
* #issues:
* index(myAccount, 'accounts[0].address[0].id') - works fine
* index(myAccount, 'accounts[].address[0].id') - doesnt work
* #Example:
* index(obj, 'data.accounts[].id') => returns array of id's
* index(obj, 'data.accounts[0].id') => returns id of 0 element from array
* index(obj, 'data.accounts[0].addresses.list[0].id') => error
* #param obj
* #param path
* #returns {any}
*/
var index = function(obj, path, isArray?, arrIndex?){
// is an array
if(typeof isArray === 'undefined') isArray = false;
// array index,
// if null, will take all indexes
if(typeof arrIndex === 'undefined') arrIndex = null;
var _arrIndex = null;
var reduceArrayTag = function(i, subArrIndex){
return i.replace(/(\[)([\d]{0,})(\])/, (i) => {
var tmp = i.match(/(\[)([\d]{0,})(\])/);
isArray = true;
if(subArrIndex){
_arrIndex = (tmp[2] !== '') ? tmp[2] : null;
}else{
arrIndex = (tmp[2] !== '') ? tmp[2] : null;
}
return '';
});
}
function byIndex(obj, i) {
// if is an array
if(isArray){
isArray = false;
i = reduceArrayTag(i, true);
// if array index is null,
// return an array of with values from every index
if(!arrIndex){
var arrValues = [];
_.forEach(obj, (el) => {
arrValues.push(index(el, i, isArray, arrIndex));
})
return arrValues;
}
// if array index is specified
var value = obj[arrIndex][i];
if(isArray){
arrIndex = _arrIndex;
}else{
arrIndex = null;
}
return value;
}else{
// remove [] from notation,
// if [] has been removed, check the index of array
i = reduceArrayTag(i, false);
return obj[i]
}
}
// reduce with the byIndex method
return path.split('.').reduce(byIndex, obj)
}
Given a JavaScript object,
var obj = { a: { b: '1', c: '2' } }
and a string
"a.b"
how can I convert the string to dot notation so I can go
var val = obj.a.b
If the string was just 'a', I could use obj[a]. But this is more complex. I imagine there is some straightforward method, but it escapes me at present.
recent note: While I'm flattered that this answer has gotten many upvotes, I am also somewhat horrified. If one needs to convert dot-notation strings like "x.a.b.c" into references, it could (maybe) be a sign that there is something very wrong going on (unless maybe you're performing some strange deserialization).
That is to say, novices who find their way to this answer must ask themselves the question "why am I doing this?"
It is of course generally fine to do this if your use case is small and you will not run into performance issues, AND you won't need to build upon your abstraction to make it more complicated later. In fact, if this will reduce code complexity and keep things simple, you should probably go ahead and do what OP is asking for. However, if that's not the case, consider if any of these apply:
case 1: As the primary method of working with your data (e.g. as your app's default form of passing objects around and dereferencing them). Like asking "how can I look up a function or variable name from a string".
This is bad programming practice (unnecessary metaprogramming specifically, and kind of violates function side-effect-free coding style, and will have performance hits). Novices who find themselves in this case, should instead consider working with array representations, e.g. ['x','a','b','c'], or even something more direct/simple/straightforward if possible: like not losing track of the references themselves in the first place (most ideal if it's only client-side or only server-side), etc. (A pre-existing unique id would be inelegant to add, but could be used if the spec otherwise requires its existence regardless.)
case 2: Working with serialized data, or data that will be displayed to the user. Like using a date as a string "1999-12-30" rather than a Date object (which can cause timezone bugs or added serialization complexity if not careful). Or you know what you're doing.
This is maybe fine. Be careful that there are no dot strings "." in your sanitized input fragments.
If you find yourself using this answer all the time and converting back and forth between string and array, you may be in the bad case, and should consider an alternative.
Here's an elegant one-liner that's 10x shorter than the other solutions:
function index(obj,i) {return obj[i]}
'a.b.etc'.split('.').reduce(index, obj)
[edit] Or in ECMAScript 6:
'a.b.etc'.split('.').reduce((o,i)=> o[i], obj)
(Not that I think eval always bad like others suggest it is (though it usually is), nevertheless those people will be pleased that this method doesn't use eval. The above will find obj.a.b.etc given obj and the string "a.b.etc".)
In response to those who still are afraid of using reduce despite it being in the ECMA-262 standard (5th edition), here is a two-line recursive implementation:
function multiIndex(obj,is) { // obj,['1','2','3'] -> ((obj['1'])['2'])['3']
return is.length ? multiIndex(obj[is[0]],is.slice(1)) : obj
}
function pathIndex(obj,is) { // obj,'1.2.3' -> multiIndex(obj,['1','2','3'])
return multiIndex(obj,is.split('.'))
}
pathIndex('a.b.etc')
Depending on the optimizations the JS compiler is doing, you may want to make sure any nested functions are not re-defined on every call via the usual methods (placing them in a closure, object, or global namespace).
edit:
To answer an interesting question in the comments:
how would you turn this into a setter as well? Not only returning the values by path, but also setting them if a new value is sent into the function? – Swader Jun 28 at 21:42
(sidenote: sadly can't return an object with a Setter, as that would violate the calling convention; commenter seems to instead be referring to a general setter-style function with side-effects like index(obj,"a.b.etc", value) doing obj.a.b.etc = value.)
The reduce style is not really suitable to that, but we can modify the recursive implementation:
function index(obj,is, value) {
if (typeof is == 'string')
return index(obj,is.split('.'), value);
else if (is.length==1 && value!==undefined)
return obj[is[0]] = value;
else if (is.length==0)
return obj;
else
return index(obj[is[0]],is.slice(1), value);
}
Demo:
> obj = {a:{b:{etc:5}}}
> index(obj,'a.b.etc')
5
> index(obj,['a','b','etc']) #works with both strings and lists
5
> index(obj,'a.b.etc', 123) #setter-mode - third argument (possibly poor form)
123
> index(obj,'a.b.etc')
123
...though personally I'd recommend making a separate function setIndex(...). I would like to end on a side-note that the original poser of the question could (should?) be working with arrays of indices (which they can get from .split), rather than strings; though there's usually nothing wrong with a convenience function.
A commenter asked:
what about arrays? something like "a.b[4].c.d[1][2][3]" ? –AlexS
Javascript is a very weird language; in general objects can only have strings as their property keys, so for example if x was a generic object like x={}, then x[1] would become x["1"]... you read that right... yup...
Javascript Arrays (which are themselves instances of Object) specifically encourage integer keys, even though you could do something like x=[]; x["puppy"]=5;.
But in general (and there are exceptions), x["somestring"]===x.somestring (when it's allowed; you can't do x.123).
(Keep in mind that whatever JS compiler you're using might choose, maybe, to compile these down to saner representations if it can prove it would not violate the spec.)
So the answer to your question would depend on whether you're assuming those objects only accept integers (due to a restriction in your problem domain), or not. Let's assume not. Then a valid expression is a concatenation of a base identifier plus some .identifiers plus some ["stringindex"]s.
Let us ignore for a moment that we can of course do other things legitimately in the grammar like identifier[0xFA7C25DD].asdf[f(4)?.[5]+k][false][null][undefined][NaN]; integers are not (that) 'special'.
Commenter's statement would then be equivalent to a["b"][4]["c"]["d"][1][2][3], though we should probably also support a.b["c\"validjsstringliteral"][3]. You'd have to check the ecmascript grammar section on string literals to see how to parse a valid string literal. Technically you'd also want to check (unlike in my first answer) that a is a valid javascript identifier.
A simple answer to your question though, if your strings don't contain commas or brackets, would be just be to match length 1+ sequences of characters not in the set , or [ or ]:
> "abc[4].c.def[1][2][\"gh\"]".match(/[^\]\[.]+/g)
// ^^^ ^ ^ ^^^ ^ ^ ^^^^^
["abc", "4", "c", "def", "1", "2", ""gh""]
If your strings don't contain escape characters or " characters, and because IdentifierNames are a sublanguage of StringLiterals (I think???) you could first convert your dots to []:
> var R=[], demoString="abc[4].c.def[1][2][\"gh\"]";
> for(var match,matcher=/^([^\.\[]+)|\.([^\.\[]+)|\["([^"]+)"\]|\[(\d+)\]/g;
match=matcher.exec(demoString); ) {
R.push(Array.from(match).slice(1).filter(x=> x!==undefined)[0]);
// extremely bad code because js regexes are weird, don't use this
}
> R
["abc", "4", "c", "def", "1", "2", "gh"]
Of course, always be careful and never trust your data. Some bad ways to do this that might work for some use cases also include:
// hackish/wrongish; preprocess your string into "a.b.4.c.d.1.2.3", e.g.:
> yourstring.replace(/]/g,"").replace(/\[/g,".").split(".")
"a.b.4.c.d.1.2.3" //use code from before
Special 2018 edit:
Let's go full-circle and do the most inefficient, horribly-overmetaprogrammed solution we can come up with... in the interest of syntactical purityhamfistery. With ES6 Proxy objects!... Let's also define some properties which (imho are fine and wonderful but) may break improperly-written libraries. You should perhaps be wary of using this if you care about performance, sanity (yours or others'), your job, etc.
// [1,2,3][-1]==3 (or just use .slice(-1)[0])
if (![1][-1])
Object.defineProperty(Array.prototype, -1, {get() {return this[this.length-1]}}); //credit to caub
// WARNING: THIS XTREME™ RADICAL METHOD IS VERY INEFFICIENT,
// ESPECIALLY IF INDEXING INTO MULTIPLE OBJECTS,
// because you are constantly creating wrapper objects on-the-fly and,
// even worse, going through Proxy i.e. runtime ~reflection, which prevents
// compiler optimization
// Proxy handler to override obj[*]/obj.* and obj[*]=...
var hyperIndexProxyHandler = {
get: function(obj,key, proxy) {
return key.split('.').reduce((o,i)=> o[i], obj);
},
set: function(obj,key,value, proxy) {
var keys = key.split('.');
var beforeLast = keys.slice(0,-1).reduce((o,i)=> o[i], obj);
beforeLast[keys[-1]] = value;
},
has: function(obj,key) {
//etc
}
};
function hyperIndexOf(target) {
return new Proxy(target, hyperIndexProxyHandler);
}
Demo:
var obj = {a:{b:{c:1, d:2}}};
console.log("obj is:", JSON.stringify(obj));
var objHyper = hyperIndexOf(obj);
console.log("(proxy override get) objHyper['a.b.c'] is:", objHyper['a.b.c']);
objHyper['a.b.c'] = 3;
console.log("(proxy override set) objHyper['a.b.c']=3, now obj is:", JSON.stringify(obj));
console.log("(behind the scenes) objHyper is:", objHyper);
if (!({}).H)
Object.defineProperties(Object.prototype, {
H: {
get: function() {
return hyperIndexOf(this); // TODO:cache as a non-enumerable property for efficiency?
}
}
});
console.log("(shortcut) obj.H['a.b.c']=4");
obj.H['a.b.c'] = 4;
console.log("(shortcut) obj.H['a.b.c'] is obj['a']['b']['c'] is", obj.H['a.b.c']);
Output:
obj is: {"a":{"b":{"c":1,"d":2}}}
(proxy override get) objHyper['a.b.c'] is: 1
(proxy override set) objHyper['a.b.c']=3, now obj is: {"a":{"b":{"c":3,"d":2}}}
(behind the scenes) objHyper is: Proxy {a: {…}}
(shortcut) obj.H['a.b.c']=4
(shortcut) obj.H['a.b.c'] is obj['a']['b']['c'] is: 4
inefficient idea: You can modify the above to dispatch based on the input argument; either use the .match(/[^\]\[.]+/g) method to support obj['keys'].like[3]['this'], or if instanceof Array, then just accept an Array as input like keys = ['a','b','c']; obj.H[keys].
Per suggestion that maybe you want to handle undefined indices in a 'softer' NaN-style manner (e.g. index({a:{b:{c:...}}}, 'a.x.c') return undefined rather than uncaught TypeError)...:
This makes sense from the perspective of "we should return undefined rather than throw an error" in the 1-dimensional index situation ({})['e.g.']==undefined, so "we should return undefined rather than throw an error" in the N-dimensional situation.
This does not make sense from the perspective that we are doing x['a']['x']['c'], which would fail with a TypeError in the above example.
That said, you'd make this work by replacing your reducing function with either:
(o,i)=> o===undefined?undefined:o[i], or
(o,i)=> (o||{})[i].
(You can make this more efficient by using a for loop and breaking/returning whenever the subresult you'd next index into is undefined, or using a try-catch if you expect such failures to be sufficiently rare.)
If you can use Lodash, there is a function, which does exactly that:
_.get(object, path, [defaultValue])
var val = _.get(obj, "a.b");
You could use lodash.get
After installing (npm i lodash.get), use it like this:
const get = require('lodash.get');
const myObj = {
user: {
firstName: 'Stacky',
lastName: 'Overflowy',
list: ['zero', 'one', 'two']
},
id: 123
};
console.log(get(myObj, 'user.firstName')); // outputs Stacky
console.log(get(myObj, 'id')); // outputs 123
console.log(get(myObj, 'user.list[1]')); // outputs one
// You can also update values
get(myObj, 'user').firstName = 'John';
A little more involved example with recursion.
function recompose(obj, string) {
var parts = string.split('.');
var newObj = obj[parts[0]];
if (parts[1]) {
parts.splice(0, 1);
var newString = parts.join('.');
return recompose(newObj, newString);
}
return newObj;
}
var obj = { a: { b: '1', c: '2', d:{a:{b:'blah'}}}};
console.log(recompose(obj, 'a.d.a.b')); //blah
2021
You don't need to pull in another dependency every time you wish for new capabilities in your program. Modern JS is very capable and the optional-chaining operator ?. is now widely supported and makes this kind of task easy as heck.
With a single line of code we can write get that takes an input object, t and string path. It works for object and arrays of any nesting level -
const get = (t, path) =>
path.split(".").reduce((r, k) => r?.[k], t)
const mydata =
{ a: { b: [ 0, { c: { d: [ "hello", "world" ] } } ] } }
console.log(get(mydata, "a.b.1.c.d.0"))
console.log(get(mydata, "a.b.1.c.d.1"))
console.log(get(mydata, "a.b.x.y.z"))
"hello"
"world"
undefined
I suggest to split the path and iterate it and reduce the object you have. This proposal works with a default value for missing properties.
const getValue = (object, keys) => keys.split('.').reduce((o, k) => (o || {})[k], object);
console.log(getValue({ a: { b: '1', c: '2' } }, 'a.b'));
console.log(getValue({ a: { b: '1', c: '2' } }, 'foo.bar.baz'));
Many years since the original post.
Now there is a great library called 'object-path'.
https://github.com/mariocasciaro/object-path
Available on NPM and BOWER
https://www.npmjs.com/package/object-path
It's as easy as:
objectPath.get(obj, "a.c.1"); //returns "f"
objectPath.set(obj, "a.j.0.f", "m");
And works for deeply nested properties and arrays.
If you expect to dereference the same path many times, building a function for each dot notation path actually has the best performance by far (expanding on the perf tests James Wilkins linked to in comments above).
var path = 'a.b.x';
var getter = new Function("obj", "return obj." + path + ";");
getter(obj);
Using the Function constructor has some of the same drawbacks as eval() in terms of security and worst-case performance, but IMO it's a badly underused tool for cases where you need a combination of extreme dynamism and high performance. I use this methodology to build array filter functions and call them inside an AngularJS digest loop. My profiles consistently show the array.filter() step taking less than 1ms to dereference and filter about 2000 complex objects, using dynamically-defined paths 3-4 levels deep.
A similar methodology could be used to create setter functions, of course:
var setter = new Function("obj", "newval", "obj." + path + " = newval;");
setter(obj, "some new val");
Other proposals are a little cryptic, so I thought I'd contribute:
Object.prop = function(obj, prop, val){
var props = prop.split('.')
, final = props.pop(), p
while(p = props.shift()){
if (typeof obj[p] === 'undefined')
return undefined;
obj = obj[p]
}
return val ? (obj[final] = val) : obj[final]
}
var obj = { a: { b: '1', c: '2' } }
// get
console.log(Object.prop(obj, 'a.c')) // -> 2
// set
Object.prop(obj, 'a.c', function(){})
console.log(obj) // -> { a: { b: '1', c: [Function] } }
var a = { b: { c: 9 } };
function value(layer, path, value) {
var i = 0,
path = path.split('.');
for (; i < path.length; i++)
if (value != null && i + 1 === path.length)
layer[path[i]] = value;
layer = layer[path[i]];
return layer;
};
value(a, 'b.c'); // 9
value(a, 'b.c', 4);
value(a, 'b.c'); // 4
This is a lot of code when compared to the much simpler eval way of doing it, but like Simon Willison says, you should never use eval.
Also, JSFiddle.
You can use the library available at npm, which simplifies this process. https://www.npmjs.com/package/dot-object
var dot = require('dot-object');
var obj = {
some: {
nested: {
value: 'Hi there!'
}
}
};
var val = dot.pick('some.nested.value', obj);
console.log(val);
// Result: Hi there!
Note if you're already using Lodash you can use the property or get functions:
var obj = { a: { b: '1', c: '2' } };
_.property('a.b')(obj); // => 1
_.get(obj, 'a.b'); // => 1
Underscore.js also has a property function, but it doesn't support dot notation.
I have extended the elegant answer by ninjagecko so that the function handles both dotted and/or array style references, and so that an empty string causes the parent object to be returned.
Here you go:
string_to_ref = function (object, reference) {
function arr_deref(o, ref, i) { return !ref ? o : (o[ref.slice(0, i ? -1 : ref.length)]) }
function dot_deref(o, ref) { return ref.split('[').reduce(arr_deref, o); }
return !reference ? object : reference.split('.').reduce(dot_deref, object);
};
See my working jsFiddle example here: http://jsfiddle.net/sc0ttyd/q7zyd/
You can obtain value of an object member by dot notation with a single line of code:
new Function('_', 'return _.' + path)(obj);
In you case:
var obj = { a: { b: '1', c: '2' } }
var val = new Function('_', 'return _.a.b')(obj);
To make it simple you may write a function like this:
function objGet(obj, path){
return new Function('_', 'return _.' + path)(obj);
}
Explanation:
The Function constructor creates a new Function object. In JavaScript every function is actually a Function object. Syntax to create a function explicitly with Function constructor is:
new Function ([arg1[, arg2[, ...argN]],] functionBody)
where arguments(arg1 to argN) must be a string that corresponds to a valid javaScript identifier and functionBody is a string containing the javaScript statements comprising the function definition.
In our case we take the advantage of string function body to retrieve object member with dot notation.
Hope it helps.
var find = function(root, path) {
var segments = path.split('.'),
cursor = root,
target;
for (var i = 0; i < segments.length; ++i) {
target = cursor[segments[i]];
if (typeof target == "undefined") return void 0;
cursor = target;
}
return cursor;
};
var obj = { a: { b: '1', c: '2' } }
find(obj, "a.b"); // 1
var set = function (root, path, value) {
var segments = path.split('.'),
cursor = root,
target;
for (var i = 0; i < segments.length - 1; ++i) {
cursor = cursor[segments[i]] || { };
}
cursor[segments[segments.length - 1]] = value;
};
set(obj, "a.k", function () { console.log("hello world"); });
find(obj, "a.k")(); // hello world
Use this function:
function dotToObject(data) {
function index(parent, key, value) {
const [mainKey, ...children] = key.split(".");
parent[mainKey] = parent[mainKey] || {};
if (children.length === 1) {
parent[mainKey][children[0]] = value;
} else {
index(parent[mainKey], children.join("."), value);
}
}
const result = Object.entries(data).reduce((acc, [key, value]) => {
if (key.includes(".")) {
index(acc, key, value);
} else {
acc[key] = value;
}
return acc;
}, {});
return result;
}
module.exports = { dotToObject };
Ex:
const user = {
id: 1,
name: 'My name',
'address.zipCode': '123',
'address.name': 'Some name',
'address.something.id': 1,
}
const mappedUser = dotToObject(user)
console.log(JSON.stringify(mappedUser, null, 2))
Output:
{
"id": 1,
"name": "My name",
"address": {
"zipCode": "123",
"name": "Some name",
"something": {
"id": 1
}
}
}
using Array Reduce function will get/set based on path provided.
I tested it with a.b.c and a.b.2.c {a:{b:[0,1,{c:7}]}} and its works for both getting key or mutating object to set value
function setOrGet(obj, path=[], newValue){
const l = typeof path === 'string' ? path.split('.') : path;
return l.reduce((carry,item, idx)=>{
const leaf = carry[item];
// is this last item in path ? cool lets set/get value
if( l.length-idx===1) {
// mutate object if newValue is set;
carry[item] = newValue===undefined ? leaf : newValue;
// return value if its a get/object if it was a set
return newValue===undefined ? leaf : obj ;
}
carry[item] = leaf || {}; // mutate if key not an object;
return carry[item]; // return object ref: to continue reduction;
}, obj)
}
console.log(
setOrGet({a: {b:1}},'a.b') === 1 ||
'Test Case: Direct read failed'
)
console.log(
setOrGet({a: {b:1}},'a.c',22).a.c===22 ||
'Test Case: Direct set failed'
)
console.log(
setOrGet({a: {b:[1,2]}},'a.b.1',22).a.b[1]===22 ||
'Test Case: Direct set on array failed'
)
console.log(
setOrGet({a: {b:{c: {e:1} }}},'a.b.c.e',22).a.b.c. e===22 ||
'Test Case: deep get failed'
)
// failed !. Thats your homework :)
console.log(
setOrGet({a: {b:{c: {e:[1,2,3,4,5]} }}},'a.b.c.e.3 ',22)
)
my personal recommendation.
do not use such a thing unless there is no other way!
i saw many examples people use it for translations for example from json; so you see function like locale('app.homepage.welcome') . this is just bad. if you already have data in an object/json; and you know path.. then just use it directly example locale().app.homepage.welcome by changing you function to return object you get typesafe, with autocomplete, less prone to typo's ..
I copied the following from Ricardo Tomasi's answer and modified to also create sub-objects that don't yet exist as necessary. It's a little less efficient (more ifs and creating of empty objects), but should be pretty good.
Also, it'll allow us to do Object.prop(obj, 'a.b', false) where we couldn't before. Unfortunately, it still won't let us assign undefined...Not sure how to go about that one yet.
/**
* Object.prop()
*
* Allows dot-notation access to object properties for both getting and setting.
*
* #param {Object} obj The object we're getting from or setting
* #param {string} prop The dot-notated string defining the property location
* #param {mixed} val For setting only; the value to set
*/
Object.prop = function(obj, prop, val){
var props = prop.split('.'),
final = props.pop(),
p;
for (var i = 0; i < props.length; i++) {
p = props[i];
if (typeof obj[p] === 'undefined') {
// If we're setting
if (typeof val !== 'undefined') {
// If we're not at the end of the props, keep adding new empty objects
if (i != props.length)
obj[p] = {};
}
else
return undefined;
}
obj = obj[p]
}
return typeof val !== "undefined" ? (obj[final] = val) : obj[final]
}
Few years later, I found this that handles scope and array. e.g. a['b']["c"].d.etc
function getScopedObj(scope, str) {
let obj=scope, arr;
try {
arr = str.split(/[\[\]\.]/) // split by [,],.
.filter(el => el) // filter out empty one
.map(el => el.replace(/^['"]+|['"]+$/g, '')); // remove string quotation
arr.forEach(el => obj = obj[el])
} catch(e) {
obj = undefined;
}
return obj;
}
window.a = {b: {c: {d: {etc: 'success'}}}}
getScopedObj(window, `a.b.c.d.etc`) // success
getScopedObj(window, `a['b']["c"].d.etc`) // success
getScopedObj(window, `a['INVALID']["c"].d.etc`) // undefined
If you wish to convert any object that contains dot notation keys into an arrayed version of those keys you can use this.
This will convert something like
{
name: 'Andy',
brothers.0: 'Bob'
brothers.1: 'Steve'
brothers.2: 'Jack'
sisters.0: 'Sally'
}
to
{
name: 'Andy',
brothers: ['Bob', 'Steve', 'Jack']
sisters: ['Sally']
}
convertDotNotationToArray(objectWithDotNotation) {
Object.entries(objectWithDotNotation).forEach(([key, val]) => {
// Is the key of dot notation
if (key.includes('.')) {
const [name, index] = key.split('.');
// If you have not created an array version, create one
if (!objectWithDotNotation[name]) {
objectWithDotNotation[name] = new Array();
}
// Save the value in the newly created array at the specific index
objectWithDotNotation[name][index] = val;
// Delete the current dot notation key val
delete objectWithDotNotation[key];
}
});
}
If you want to convert a string dot notation into an object, I've made a handy little helper than can turn a string like a.b.c.d with a value of e with dotPathToObject("a.b.c.d", "value") returning this:
{
"a": {
"b": {
"c": {
"d": "value"
}
}
}
}
https://gist.github.com/ahallora/9731d73efb15bd3d3db647efa3389c12
Solution:
function deepFind(key, data){
return key.split('.').reduce((ob,i)=> ob?.[i], data)
}
Usage:
const obj = {
company: "Pet Shop",
person: {
name: "John"
},
animal: {
name: "Lucky"
}
}
const company = deepFind("company", obj)
const personName = deepFind("person.name", obj)
const animalName = deepFind("animal.name", obj)
Here is my implementation
Implementation 1
Object.prototype.access = function() {
var ele = this[arguments[0]];
if(arguments.length === 1) return ele;
return ele.access.apply(ele, [].slice.call(arguments, 1));
}
Implementation 2 (using array reduce instead of slice)
Object.prototype.access = function() {
var self = this;
return [].reduce.call(arguments,function(prev,cur) {
return prev[cur];
}, self);
}
Examples:
var myobj = {'a':{'b':{'c':{'d':'abcd','e':[11,22,33]}}}};
myobj.access('a','b','c'); // returns: {'d':'abcd', e:[0,1,2,3]}
myobj.a.b.access('c','d'); // returns: 'abcd'
myobj.access('a','b','c','e',0); // returns: 11
it can also handle objects inside arrays as for
var myobj2 = {'a': {'b':[{'c':'ab0c'},{'d':'ab1d'}]}}
myobj2.access('a','b','1','d'); // returns: 'ab1d'
I used this code in my project
const getValue = (obj, arrPath) => (
arrPath.reduce((x, y) => {
if (y in x) return x[y]
return {}
}, obj)
)
Usage:
const obj = { id: { user: { local: 104 } } }
const path = [ 'id', 'user', 'local' ]
getValue(obj, path) // return 104
Using object-scan seems a bit overkill, but you can simply do
// const objectScan = require('object-scan');
const get = (obj, p) => objectScan([p], { abort: true, rtn: 'value' })(obj);
const obj = { a: { b: '1', c: '2' } };
console.log(get(obj, 'a.b'));
// => 1
console.log(get(obj, '*.c'));
// => 2
.as-console-wrapper {max-height: 100% !important; top: 0}
<script src="https://bundle.run/object-scan#13.7.1"></script>
Disclaimer: I'm the author of object-scan
There are a lot more advanced examples in the readme.
This is one of those cases, where you ask 10 developers and you get 10 answers.
Below is my [simplified] solution for OP, using dynamic programming.
The idea is that you would pass an existing DTO object that you wish to UPDATE. This makes the method most useful in the case where you have a form with several input elements having name attributes set with dot (fluent) syntax.
Example use:
<input type="text" name="person.contact.firstName" />
Code snippet:
const setFluently = (obj, path, value) => {
if (typeof path === "string") {
return setFluently(obj, path.split("."), value);
}
if (path.length <= 1) {
obj[path[0]] = value;
return obj;
}
const key = path[0];
obj[key] = setFluently(obj[key] ? obj[key] : {}, path.slice(1), value);
return obj;
};
const origObj = {
a: {
b: "1",
c: "2"
}
};
setFluently(origObj, "a.b", "3");
setFluently(origObj, "a.c", "4");
console.log(JSON.stringify(origObj, null, 3));
function at(obj, path, val = undefined) {
// If path is an Array,
if (Array.isArray(path)) {
// it returns the mapped array for each result of the path
return path.map((path) => at(obj, path, val));
}
// Uniting several RegExps into one
const rx = new RegExp(
[
/(?:^(?:\.\s*)?([_a-zA-Z][_a-zA-Z0-9]*))/,
/(?:^\[\s*(\d+)\s*\])/,
/(?:^\[\s*'([^']*(?:\\'[^']*)*)'\s*\])/,
/(?:^\[\s*"([^"]*(?:\\"[^"]*)*)"\s*\])/,
/(?:^\[\s*`([^`]*(?:\\`[^`]*)*)`\s*\])/,
]
.map((r) => r.source)
.join("|")
);
let rm;
while (rm = rx.exec(path.trim())) {
// Matched resource
let [rf, rp] = rm.filter(Boolean);
// If no one matches found,
if (!rm[1] && !rm[2]) {
// it will replace escape-chars
rp = rp.replace(/\\(.)/g, "$1");
}
// If the new value is set,
if ("undefined" != typeof val && path.length == rf.length) {
// assign a value to the object property and return it
return (obj[rp] = val);
}
// Going one step deeper
obj = obj[rp];
// Removing a step from the path
path = path.substr(rf.length).trim();
}
if (path) {
throw new SyntaxError();
}
return obj;
}
// Test object schema
let o = { a: { b: [ [ { c: { d: { '"e"': { f: { g: "xxx" } } } } } ] ] } };
// Print source object
console.log(JSON.stringify(o));
// Set value
console.log(at(o, '.a["b"][0][0].c[`d`]["\\"e\\""][\'f\']["g"]', "zzz"));
// Get value
console.log(at(o, '.a["b"][0][0].c[`d`]["\\"e\\""][\'f\']["g"]'));
// Print result object
console.log(JSON.stringify(o));
Here is my code without using eval. It’s easy to understand too.
function value(obj, props) {
if (!props)
return obj;
var propsArr = props.split('.');
var prop = propsArr.splice(0, 1);
return value(obj[prop], propsArr.join('.'));
}
var obj = { a: { b: '1', c: '2', d:{a:{b:'blah'}}}};
console.log(value(obj, 'a.d.a.b')); // Returns blah
Yes, extending base prototypes is not usually good idea but, if you keep all extensions in one place, they might be useful.
So, here is my way to do this.
Object.defineProperty(Object.prototype, "getNestedProperty", {
value : function (propertyName) {
var result = this;
var arr = propertyName.split(".");
while (arr.length && result) {
result = result[arr.shift()];
}
return result;
},
enumerable: false
});
Now you will be able to get nested property everywhere without importing module with function or copy/pasting function.
Example:
{a:{b:11}}.getNestedProperty('a.b'); // Returns 11
The Next.js extension broke Mongoose in my project. Also I've read that it might break jQuery. So, never do it in the Next.js way:
Object.prototype.getNestedProperty = function (propertyName) {
var result = this;
var arr = propertyName.split(".");
while (arr.length && result) {
result = result[arr.shift()];
}
return result;
};
This is my extended solution proposed by ninjagecko.
For me, simple string notation was not enough, so the below version supports things like:
index(obj, 'data.accounts[0].address[0].postcode');
/**
* Get object by index
* #supported
* - arrays supported
* - array indexes supported
* #not-supported
* - multiple arrays
* #issues:
* index(myAccount, 'accounts[0].address[0].id') - works fine
* index(myAccount, 'accounts[].address[0].id') - doesnt work
* #Example:
* index(obj, 'data.accounts[].id') => returns array of id's
* index(obj, 'data.accounts[0].id') => returns id of 0 element from array
* index(obj, 'data.accounts[0].addresses.list[0].id') => error
* #param obj
* #param path
* #returns {any}
*/
var index = function(obj, path, isArray?, arrIndex?){
// is an array
if(typeof isArray === 'undefined') isArray = false;
// array index,
// if null, will take all indexes
if(typeof arrIndex === 'undefined') arrIndex = null;
var _arrIndex = null;
var reduceArrayTag = function(i, subArrIndex){
return i.replace(/(\[)([\d]{0,})(\])/, (i) => {
var tmp = i.match(/(\[)([\d]{0,})(\])/);
isArray = true;
if(subArrIndex){
_arrIndex = (tmp[2] !== '') ? tmp[2] : null;
}else{
arrIndex = (tmp[2] !== '') ? tmp[2] : null;
}
return '';
});
}
function byIndex(obj, i) {
// if is an array
if(isArray){
isArray = false;
i = reduceArrayTag(i, true);
// if array index is null,
// return an array of with values from every index
if(!arrIndex){
var arrValues = [];
_.forEach(obj, (el) => {
arrValues.push(index(el, i, isArray, arrIndex));
})
return arrValues;
}
// if array index is specified
var value = obj[arrIndex][i];
if(isArray){
arrIndex = _arrIndex;
}else{
arrIndex = null;
}
return value;
}else{
// remove [] from notation,
// if [] has been removed, check the index of array
i = reduceArrayTag(i, false);
return obj[i]
}
}
// reduce with the byIndex method
return path.split('.').reduce(byIndex, obj)
}
I'll explain by example:
Elvis Operator (?: )
The "Elvis operator" is a shortening
of Java's ternary operator. One
instance of where this is handy is for
returning a 'sensible default' value
if an expression resolves to false or
null. A simple example might look like
this:
def gender = user.male ? "male" : "female" //traditional ternary operator usage
def displayName = user.name ?: "Anonymous" //more compact Elvis operator
Safe Navigation Operator (?.)
The Safe Navigation operator is used
to avoid a NullPointerException.
Typically when you have a reference to
an object you might need to verify
that it is not null before accessing
methods or properties of the object.
To avoid this, the safe navigation
operator will simply return null
instead of throwing an exception, like
so:
def user = User.find( "admin" ) //this might be null if 'admin' does not exist
def streetName = user?.address?.street //streetName will be null if user or user.address is null - no NPE thrown
You can use the logical 'OR' operator in place of the Elvis operator:
For example displayname = user.name || "Anonymous" .
But Javascript currently doesn't have the other functionality. I'd recommend looking at CoffeeScript if you want an alternative syntax. It has some shorthand that is similar to what you are looking for.
For example The Existential Operator
zip = lottery.drawWinner?().address?.zipcode
Function shortcuts
()-> // equivalent to function(){}
Sexy function calling
func 'arg1','arg2' // equivalent to func('arg1','arg2')
There is also multiline comments and classes. Obviously you have to compile this to javascript or insert into the page as <script type='text/coffeescript>' but it adds a lot of functionality :) . Using <script type='text/coffeescript'> is really only intended for development and not production.
I think the following is equivalent to the safe navigation operator, although a bit longer:
var streetName = user && user.address && user.address.street;
streetName will then be either the value of user.address.street or undefined.
If you want it to default to something else you can combine with the above shortcut or to give:
var streetName = (user && user.address && user.address.street) || "Unknown Street";
2020 Update
JavaScript now has equivalents for both the Elvis Operator and the Safe Navigation Operator.
Safe Property Access
The optional chaining operator (?.) is currently a stage 4 ECMAScript proposal. You can use it today with Babel.
// `undefined` if either `a` or `b` are `null`/`undefined`. `a.b.c` otherwise.
const myVariable = a?.b?.c;
The logical AND operator (&&) is the "old", more-verbose way to handle this scenario.
const myVariable = a && a.b && a.b.c;
Providing a Default
The nullish coalescing operator (??) is currently a stage 4 ECMAScript proposal. You can use it today with Babel. It allows you to set a default value if the left-hand side of the operator is a nullary value (null/undefined).
const myVariable = a?.b?.c ?? 'Some other value';
// Evaluates to 'Some other value'
const myVariable2 = null ?? 'Some other value';
// Evaluates to ''
const myVariable3 = '' ?? 'Some other value';
The logical OR operator (||) is an alternative solution with slightly different behavior. It allows you to set a default value if the left-hand side of the operator is falsy. Note that the result of myVariable3 below differs from myVariable3 above.
const myVariable = a?.b?.c || 'Some other value';
// Evaluates to 'Some other value'
const myVariable2 = null || 'Some other value';
// Evaluates to 'Some other value'
const myVariable3 = '' || 'Some other value';
Javascript's logical OR operator is short-circuiting and can replace your "Elvis" operator:
var displayName = user.name || "Anonymous";
However, to my knowledge there's no equivalent to your ?. operator.
I've occasionally found the following idiom useful:
a?.b?.c
can be rewritten as:
((a||{}).b||{}).c
This takes advantage of the fact that getting unknown attributes on an object returns undefined, rather than throwing an exception as it does on null or undefined, so we replace null and undefined with an empty object before navigating.
i think lodash _.get() can help here, as in _.get(user, 'name'), and more complex tasks like _.get(o, 'a[0].b.c', 'default-value')
There is currently a draft spec:
https://github.com/tc39/proposal-optional-chaining
https://tc39.github.io/proposal-optional-chaining/
For now, though, I like to use lodash get(object, path [,defaultValue]) or dlv delve(obj, keypath)
Update (as of Dec 23, 2019):
optional chaining has moved to stage 4
For the former, you can use ||. The Javascript "logical or" operator, rather than simply returning canned true and false values, follows the rule of returning its left argument if it is true, and otherwise evaluating and returning its right argument. When you're only interested in the truth value it works out the same, but it also means that foo || bar || baz returns the leftmost one of foo, bar, or baz that contains a true value.
You won't find one that can distinguish false from null, though, and 0 and empty string are false values, so avoid using the value || default construct where value can legitimately be 0 or "".
Yes, there is! 🍾
Optional chaining is in stage 4 and this enables you to use the user?.address?.street formula.
If you can't wait the release, install #babel/plugin-proposal-optional-chaining and you can use it.
Here are my settings which works for me, or just read Nimmo's article.
// package.json
{
"name": "optional-chaining-test",
"version": "1.0.0",
"main": "index.js",
"devDependencies": {
"#babel/plugin-proposal-optional-chaining": "7.2.0",
"#babel/core": "7.2.0",
"#babel/preset-env": "^7.5.5"
}
...
}
// .babelrc
{
"presets": [
[
"#babel/preset-env",
{
"debug": true
}
]
],
"plugins": [
"#babel/plugin-proposal-optional-chaining"
]
}
// index.js
console.log(user?.address?.street); // it works
Here's a simple elvis operator equivalent:
function elvis(object, path) {
return path ? path.split('.').reduce(function (nestedObject, key) {
return nestedObject && nestedObject[key];
}, object) : object;
}
> var o = { a: { b: 2 }, c: 3 };
> elvis(o)
{ a: { b: 2 }, c: 3 }
> elvis(o, 'a');
{ b: 2 }
> elvis(o, 'a.b');
2
> elvis(o, 'x');
undefined
You can achieve roughly the same effect by saying:
var displayName = user.name || "Anonymous";
UPDATE SEP 2019
Yes, JS now supports this.
Optional chaining is coming soon to v8 read more
This is more commonly known as a null-coalescing operator. Javascript does not have one.
I have a solution for that, tailor it to your own needs, an excerpt from one of my libs:
elvisStructureSeparator: '.',
// An Elvis operator replacement. See:
// http://coffeescript.org/ --> The Existential Operator
// http://fantom.org/doc/docLang/Expressions.html#safeInvoke
//
// The fn parameter has a SPECIAL SYNTAX. E.g.
// some.structure['with a selector like this'].value transforms to
// 'some.structure.with a selector like this.value' as an fn parameter.
//
// Configurable with tulebox.elvisStructureSeparator.
//
// Usage examples:
// tulebox.elvis(scope, 'arbitrary.path.to.a.function', fnParamA, fnParamB, fnParamC);
// tulebox.elvis(this, 'currentNode.favicon.filename');
elvis: function (scope, fn) {
tulebox.dbg('tulebox.elvis(' + scope + ', ' + fn + ', args...)');
var implicitMsg = '....implicit value: undefined ';
if (arguments.length < 2) {
tulebox.dbg(implicitMsg + '(1)');
return undefined;
}
// prepare args
var args = [].slice.call(arguments, 2);
if (scope === null || fn === null || scope === undefined || fn === undefined
|| typeof fn !== 'string') {
tulebox.dbg(implicitMsg + '(2)');
return undefined;
}
// check levels
var levels = fn.split(tulebox.elvisStructureSeparator);
if (levels.length < 1) {
tulebox.dbg(implicitMsg + '(3)');
return undefined;
}
var lastLevel = scope;
for (var i = 0; i < levels.length; i++) {
if (lastLevel[levels[i]] === undefined) {
tulebox.dbg(implicitMsg + '(4)');
return undefined;
}
lastLevel = lastLevel[levels[i]];
}
// real return value
if (typeof lastLevel === 'function') {
var ret = lastLevel.apply(scope, args);
tulebox.dbg('....function value: ' + ret);
return ret;
} else {
tulebox.dbg('....direct value: ' + lastLevel);
return lastLevel;
}
},
works like a charm. Enjoy the less pain!
You could roll your own:
function resolve(objectToGetValueFrom, stringOfDotSeparatedParameters) {
var returnObject = objectToGetValueFrom,
parameters = stringOfDotSeparatedParameters.split('.'),
i,
parameter;
for (i = 0; i < parameters.length; i++) {
parameter = parameters[i];
returnObject = returnObject[parameter];
if (returnObject === undefined) {
break;
}
}
return returnObject;
};
And use it like this:
var result = resolve(obj, 'a.b.c.d');
* result is undefined if any one of a, b, c or d is undefined.
I read this article (https://www.beyondjava.net/elvis-operator-aka-safe-navigation-javascript-typescript) and modified the solution using Proxies.
function safe(obj) {
return new Proxy(obj, {
get: function(target, name) {
const result = target[name];
if (!!result) {
return (result instanceof Object)? safe(result) : result;
}
return safe.nullObj;
},
});
}
safe.nullObj = safe({});
safe.safeGet= function(obj, expression) {
let safeObj = safe(obj);
let safeResult = expression(safeObj);
if (safeResult === safe.nullObj) {
return undefined;
}
return safeResult;
}
You call it like this:
safe.safeGet(example, (x) => x.foo.woo)
The result will be undefined for an expression that encounters null or undefined along its path. You could go wild and modify the Object prototype!
Object.prototype.getSafe = function (expression) {
return safe.safeGet(this, expression);
};
example.getSafe((x) => x.foo.woo);
Jumping in very late, there's a proposal[1] for optional chaining currently at stage 2, with a babel plugin[2] available. It's not currently in any browser I am aware of.
https://github.com/tc39/proposal-optional-chaining
https://www.npmjs.com/package/#babel/plugin-proposal-optional-chaining
This was a problem for me for a long time. I had to come up with a solution that can be easily migrated once we get Elvis operator or something.
This is what I use; works for both arrays and objects
put this in tools.js file or something
// this will create the object/array if null
Object.prototype.__ = function (prop) {
if (this[prop] === undefined)
this[prop] = typeof prop == 'number' ? [] : {}
return this[prop]
};
// this will just check if object/array is null
Object.prototype._ = function (prop) {
return this[prop] === undefined ? {} : this[prop]
};
usage example:
let student = {
classes: [
'math',
'whatev'
],
scores: {
math: 9,
whatev: 20
},
loans: [
200,
{ 'hey': 'sup' },
500,
300,
8000,
3000000
]
}
// use one underscore to test
console.log(student._('classes')._(0)) // math
console.log(student._('classes')._(3)) // {}
console.log(student._('sports')._(3)._('injuries')) // {}
console.log(student._('scores')._('whatev')) // 20
console.log(student._('blabla')._('whatev')) // {}
console.log(student._('loans')._(2)) // 500
console.log(student._('loans')._(1)._('hey')) // sup
console.log(student._('loans')._(6)._('hey')) // {}
// use two underscores to create if null
student.__('loans').__(6)['test'] = 'whatev'
console.log(student.__('loans').__(6).__('test')) // whatev
well I know it makes the code a bit unreadable but it's a simple one liner solution and works great. I hope it helps someone :)
This was an interesting solution for the safe navigation operator using some mixin..
http://jsfiddle.net/avernet/npcmv/
// Assume you have the following data structure
var companies = {
orbeon: {
cfo: "Erik",
cto: "Alex"
}
};
// Extend Underscore.js
_.mixin({
// Safe navigation
attr: function(obj, name) { return obj == null ? obj : obj[name]; },
// So we can chain console.log
log: function(obj) { console.log(obj); }
});
// Shortcut, 'cause I'm lazy
var C = _(companies).chain();
// Simple case: returns Erik
C.attr("orbeon").attr("cfo").log();
// Simple case too, no CEO in Orbeon, returns undefined
C.attr("orbeon").attr("ceo").log();
// IBM unknown, but doesn't lead to an error, returns undefined
C.attr("ibm").attr("ceo").log();
I created a package that makes this a lot easier to use.
NPM jsdig
Github jsdig
You can handle simple things like and object:
const world = {
locations: {
europe: 'Munich',
usa: 'Indianapolis'
}
};
world.dig('locations', 'usa');
// => 'Indianapolis'
world.dig('locations', 'asia', 'japan');
// => 'null'
or a little more complicated:
const germany = () => 'germany';
const world = [0, 1, { location: { europe: germany } }, 3];
world.dig(2, 'location', 'europe') === germany;
world.dig(2, 'location', 'europe')() === 'germany';
?? would work in js which is equivalent to ?: in kotlin
Personally i use
function e(e,expr){try{return eval(expr);}catch(e){return null;}};
and for example safe get:
var a = e(obj,'e.x.y.z.searchedField');