I get from the server a list of objects
[{name:'test01', age:10},{name:'test02', age:20},{name:'test03', age:30}]
I load them into html controls for the user to edit.
Then there is a button to bulk save the entire list back to the database.
Instead of sending the whole list I only want to send the subset of objects that were changed.
It can be any number of items in the array. I want to do something similar to frameworks like Angular that mark an object property like "pristine" when no change has been done to it. Then use that flag to only post to the server the items that are not "pristine", the ones that were modified.
Here is a function down below that will return an array/object of changed objects when supplied with an old array/object of objects and a new array of objects:
// intended to compare objects of identical shape; ideally static.
//
// any top-level key with a primitive value which exists in `previous` but not
// in `current` returns `undefined` while vice versa yields a diff.
//
// in general, the input type determines the output type. that is if `previous`
// and `current` are objects then an object is returned. if arrays then an array
// is returned, etc.
const getChanges = (previous, current) => {
if (isPrimitive(previous) && isPrimitive(current)) {
if (previous === current) {
return "";
}
return current;
}
if (isObject(previous) && isObject(current)) {
const diff = getChanges(Object.entries(previous), Object.entries(current));
return diff.reduce((merged, [key, value]) => {
return {
...merged,
[key]: value
}
}, {});
}
const changes = [];
if (JSON.stringify(previous) === JSON.stringify(current)) {
return changes;
}
for (let i = 0; i < current.length; i++) {
const item = current[i];
if (JSON.stringify(item) !== JSON.stringify(previous[i])) {
changes.push(item);
}
}
return changes;
};
For Example:
const arr1 = [1, 2, 3, 4]
const arr2 = [4, 4, 2, 4]
console.log(getChanges(arr1, arr2)) // [4,4,2]
const obj1 = {
foo: "bar",
baz: [
1, 2, 3
],
qux: {
hello: "world"
},
bingo: "name-o",
}
const obj2 = {
foo: "barx",
baz: [
1, 2, 3, 4
],
qux: {
hello: null
},
bingo: "name-o",
}
console.log(getChanges(obj1.foo, obj2.foo)) // barx
console.log(getChanges(obj1.bingo, obj2.bingo)) // ""
console.log(getChanges(obj1.baz, obj2.baz)) // [4]
console.log(getChanges(obj1, obj2)) // {foo:'barx',baz:[1,2,3,4],qux:{hello:null}}
const obj3 = [{ name: 'test01', age: 10 }, { name: 'test02', age: 20 }, { name: 'test03', age: 30 }]
const obj4 = [{ name: 'test01', age: 10 }, { name: 'test02', age: 20 }, { name: 'test03', age: 20 }]
console.log(getChanges(obj3, obj4)) // [{name:'test03', age:20}]
Utility functions used:
// not required for this example but aid readability of the main function
const typeOf = o => Object.prototype.toString.call(o);
const isObject = o => o !== null && !Array.isArray(o) && typeOf(o).split(" ")[1].slice(0, -1) === "Object";
const isPrimitive = o => {
switch (typeof o) {
case "object": {
return false;
}
case "function": {
return false;
}
default: {
return true;
}
}
};
You would simply have to export the full list of edited values client side, compare it with the old list, and then send the list of changes off to the server.
Hope this helps!
Here are a few ideas.
Use a framework. You spoke of Angular.
Use Proxies, though Internet Explorer has no support for it.
Instead of using classic properties, maybe use Object.defineProperty's set/get to achieve some kind of change tracking.
Use getter/setting functions to store data instead of properties: getName() and setName() for example. Though this the older way of doing what defineProperty now does.
Whenever you bind your data to your form elements, set a special property that indicates if the property has changed. Something like __hasChanged. Set to true if any property on the object changes.
The old school bruteforce way: keep your original list of data that came from the server, deep copy it into another list, bind your form controls to the new list, then when the user clicks submit, compare the objects in the original list to the objects in the new list, plucking out the changed ones as you go. Probably the easiest, but not necessarily the cleanest.
A different take on #6: Attach a special property to each object that always returns the original version of the object:
var myData = [{name: "Larry", age: 47}];
var dataWithCopyOfSelf = myData.map(function(data) {
Object.assign({}, data, { original: data });
});
// now bind your form to dataWithCopyOfSelf.
Of course, this solution assumes a few things: (1) that your objects are flat and simple since Object.assign() doesn't deep copy, (2) that your original data set will never be changed, and (3) that nothing ever touches the contents of original.
There are a multitude of solutions out there.
With ES6 we can use Proxy
to accomplish this task: intercept an Object write, and mark it as dirty.
Proxy allows to create a handler Object that can trap, manipulate, and than forward changes to the original target Object, basically allowing to reconfigure its behavior.
The trap we're going to adopt to intercept Object writes is the handler set().
At this point we can add a non-enumerable property flag like i.e: _isDirty using Object.defineProperty() to mark our Object as modified, dirty.
When using traps (in our case the handler's set()) no changes are applied nor reflected to the Objects, therefore we need to forward the argument values to the target Object using Reflect.set().
Finally, to retrieve the modified objects, filter() the Array with our proxy Objects in search of those having its own Property "_isDirty".
// From server:
const dataOrg = [
{id:1, name:'a', age:10},
{id:2, name:'b', age:20},
{id:3, name:'c', age:30}
];
// Mirror data from server to observable Proxies:
const data = dataOrg.map(ob => new Proxy(ob, {
set() {
Object.defineProperty(ob, "_isDirty", {value: true}); // Flag
return Reflect.set(...arguments); // Forward trapped args to ob
}
}));
// From now on, use proxied data. Let's change some values:
data[0].name = "Lorem";
data[0].age = 42;
data[2].age = 31;
// Collect modified data
const dataMod = data.filter(ob => ob.hasOwnProperty("_isDirty"));
// Test what we're about to send back to server:
console.log(JSON.stringify(dataMod, null, 2));
Without using .defineProperty()
If for some reason you don't feel comfortable into tapping into the original object adding extra properties as flags, you could instead populate immediately
the dataMod (array with modified Objects) with references:
const dataOrg = [
{id:1, name:'a', age:10},
{id:2, name:'b', age:20},
{id:3, name:'c', age:30}
];
// Prepare array to hold references to the modified Objects
const dataMod = [];
const data = dataOrg.map(ob => new Proxy(ob, {
set() {
if (dataMod.indexOf(ob) < 0) dataMod.push(ob); // Push reference
return Reflect.set(...arguments);
}
}));
data[0].name = "Lorem";
data[0].age = 42;
data[2].age = 31;
console.log(JSON.stringify(dataMod, null, 2));
Can I Use - Proxy (IE)
Proxy - handler.set()
Global Objects - Reflect
Reflect.set()
Object.defineProperty()
Object.hasOwnProperty()
Without having to get fancy with prototype properties you could simply store them in another array whenever your form control element detects a change
Something along the lines of:
var modified = [];
data.forEach(function(item){
var domNode = // whatever you use to match data to form control element
domNode.addEventListener('input',function(){
if(modified.indexOf(item) === -1){
modified.push(item);
}
});
});
Then send the modified array to server when it's time to save
Why not use Ember.js observable properties ? You can use the Ember.observer function to get and set changes in your data.
Ember.Object.extend({
valueObserver: Ember.observer('value', function(sender, key, value, rev) {
// Executes whenever the "value" property changes
// See the addObserver method for more information about the callback arguments
})
});
The Ember.object actually does a lot of heavy lifting for you.
Once you define your object, add an observer like so:
object.addObserver('propertyKey', targetObject, targetAction)
My idea is to sort object keys and convert object to be string to compare:
// use this function to sort keys, and save key=>value in an array
function objectSerilize(obj) {
let keys = Object.keys(obj)
let results = []
keys.sort((a, b) => a > b ? -1 : a < b ? 1 : 0)
keys.forEach(key => {
let value = obj[key]
if (typeof value === 'object') {
value = objectSerilize(value)
}
results.push({
key,
value,
})
})
return results
}
// use this function to compare
function compareObject(a, b) {
let aStr = JSON.stringify(objectSerilize(a))
let bStr = JSON.stringify(objectSerilize(b))
return aStr === bStr
}
This is what I think up.
It would be cleanest, I’d think to have the object emit an event when a property is added or removed or modified.
A simplistic implementation could involve an array with the object keys; whenever a setter or heck the constructor returns this, it first calls a static function returning a promise; resolving: map with changed values in the array: things added, things removed, or neither. So one could get(‘changed’) or so forth; returning an array.
Similarly every setter can emit an event with arguments for initial value and new value.
Assuming classes are used, you could easily have a static method in a parent generic class that can be called through its constructor and so really you could simplify most of this by passing the object either to itself, or to the parent through super(checkMeProperty).
Application
I am working on a simple web application that is built on top of AngularJS. The application should be able to work offline as well as online. When the user is offline, the changes to the data is stored locally. Therefore, the id's that is used within this application in offline mode is only temporary id's, they get replaced when uploaded to the server
Problem
The data that are used in the application consists of complex objects (with relations/references to other objects). When i am saving to the server, i wanted the views to get updated with the new "real" id's.
However, since JavaScript works with objects as references im not able to do what i want to: $scope.data = newdata
This is not overwriting $scope.data but creates a new object. The old reference to the old data is still there.
Simplified example
var x = {id: 1, name: "myObject"}
var c = x // c = {id: 1, name: "myObject"}
x = {id: 2, name: "myNewObject"}
// c = {id: 1, name: "myObject"}
As you can see, c is still a reference to the old object. In practice, this causes that my view isn't updated with new data since it's still bound to the old data.
What i need to is to overwrite the properties of, in this example, x. I need to do this recursively since my real objects are complex, however it shouldn't enter any circular references, since this will probably cause stack overflow. If i am overwriting a with b and a has properties that b hasn't got, those properties should be removed.
What i need
I need some sort of function that overwrites all properties in a (old object) with the properties in b (new object). All properties that exists in a but not in b should be removed.
If your environment supports ECMAScript 2015, you can use Object.assign():
'use strict'
let one = { a: 1, b: 2, c: 3 };
let two = { b: 20, c: 30, d: 40 };
let three = Object.assign({}, one, two);
console.log(three);
// will output: Object {a: 1, b: 20, c: 30, d: 40}
(let is the new locally scoped version of var in ECMAScript 2015) more...
So in the case of your simple example:
var x = { id: 1, name: "myObject" };
Object.assign(x, { id: 2, name: "myNewObject" });
console.log(x);
// will output: Object {id: 2, name: "myNewObject"}
Using the "extend" method which is available in underscore and jquery:
//Clear all the 'old' properties from the object
for (prop in old_object) {delete old_object[prop]}
//Insert the new ones
$.extend(old_object, new_object)
I found a solution after some thinking. It's probably not the most efficient solution, but it does the job for me. The time complexity could probably be better, and all suggestions of improvement are welcome. First parameter is the object to be extended, the second the one to extend with. The third is supposed to be a boolean, indicating whether the properties in a that doesn't exist in b should be removed or not.
function extend(_a,_b,remove){
remove = remove === undefined ? false : remove;
var a_traversed = [],
b_traversed = [];
function _extend(a,b) {
if (a_traversed.indexOf(a) == -1 && b_traversed.indexOf(b) == -1){
a_traversed.push(a);
b_traversed.push(b);
if (a instanceof Array){
for (var i = 0; i < b.length; i++) {
if (a[i]){ // If element exists, keep going recursive so we don't lose the references
a[i] = _extend(a[i],b[i]);
} else {
a[i] = b[i]; // Object doesn't exist, no reference to lose
}
}
if (remove && b.length < a.length) { // Do we have fewer elements in the new object?
a.splice(b.length, a.length - b.length);
}
}
else if (a instanceof Object){
for (var x in b) {
if (a.hasOwnProperty(x)) {
a[x] = _extend(a[x], b[x]);
} else {
a[x] = b[x];
}
}
if (remove) for (var x in a) {
if (!b.hasOwnProperty(x)) {
delete a[x];
}
}
}
else{
return b;
}
return a;
}
}
_extend(_a,_b);
}
I'm adding an answer, even though everyone has explained both why and solutions.
The reason I'm adding answer, is because I've searched for this answer a few times over the years and always basically come to the same 2/3 SO questions. I put the solutions in the too-hard-basket, because the code I've been working with has many modules all following similar design patterns; it's just been too much work to try and resolve what boiled down to the same issue you were having.
What I've learned, and hopefully it holds some value for others out there now that I've actually re-factored our codebase to avoid this issue (sometimes maybe its unavoidable, but sometimes it definitely is), is to avoid using 'static private variables' to reference Objects.
This can probably be more genericised, but take for example:
var G = {
'someKey' : {
'foo' : 'bar'
}
};
G.MySingletonClass = (function () {
var _private_static_data = G.someKey; // referencing an Object
return {
/**
* a method that returns the value of _private_static_data
*
* #method log
**/
log: function () {
return _private_static_data;
} // eom - log()
}; // end of return block
}()); // end of Class
console.log(G.MySingletonClass.log());
G.someKey = {
'baz':'fubar'
};
console.log(G.MySingletonClass.log());
http://jsfiddle.net/goxdebfh/1/
As you can see, same problem experienced by the Questioner. In my case, and this use of private static variables referencing Objects was everywhere, all I needed to do was directly lookup G.someKey; instead of storing it as a convenience variable for my Class. The end result (though lengthier as a result of inconvenience) works very well:
var G = {
'someKey' : {
'foo' : 'bar'
}
};
G.MySingletonClass = (function () {
return {
/**
* a method that returns the value of _private_static_data
*
* #method log
**/
log: function () {
return G.someKey;
} // eom - log()
}; // end of return block
}()); // end of Class
console.log(G.MySingletonClass.log());
G.someKey = {
'baz':'fubar'
};
console.log(G.MySingletonClass.log());
http://jsfiddle.net/vv2d7juy/1/
So yeah, maybe nothing new given the question has been solved, but I felt compelled to share that because I was even lead to believe that the first example was the correct way to do things. Maybe in some cases it is, it definitely didn't turn out to be.
Hopefully that helps someone, somewhere!
Given an object:
let myObject = {
"ircEvent": "PRIVMSG",
"method": "newURI",
"regex": "^http://.*"
};
How do I remove the property regex to end up with the following myObject?
let myObject = {
"ircEvent": "PRIVMSG",
"method": "newURI"
};
To remove a property from an object (mutating the object), you can do it like this:
delete myObject.regex;
// or,
delete myObject['regex'];
// or,
var prop = "regex";
delete myObject[prop];
Demo
var myObject = {
"ircEvent": "PRIVMSG",
"method": "newURI",
"regex": "^http://.*"
};
delete myObject.regex;
console.log(myObject);
For anyone interested in reading more about it, Stack Overflow user kangax has written an incredibly in-depth blog post about the delete statement on their blog, Understanding delete. It is highly recommended.
If you'd like a new object with all the keys of the original except some, you could use destructuring.
Demo
let myObject = {
"ircEvent": "PRIVMSG",
"method": "newURI",
"regex": "^http://.*"
};
// assign the key regex to the variable _ indicating it will be unused
const {regex: _, ...newObj} = myObject;
console.log(newObj); // has no 'regex' key
console.log(myObject); // remains unchanged
Objects in JavaScript can be thought of as maps between keys and values. The delete operator is used to remove these keys, more commonly known as object properties, one at a time.
var obj = {
myProperty: 1
}
console.log(obj.hasOwnProperty('myProperty')) // true
delete obj.myProperty
console.log(obj.hasOwnProperty('myProperty')) // false
The delete operator does not directly free memory, and it differs from simply assigning the value of null or undefined to a property, in that the property itself is removed from the object. Note that if the value of a deleted property was a reference type (an object), and another part of your program still holds a reference to that object, then that object will, of course, not be garbage collected until all references to it have disappeared.
delete will only work on properties whose descriptor marks them as configurable.
Old question, modern answer. Using object destructuring, an ECMAScript 6 feature, it's as simple as:
const { a, ...rest } = { a: 1, b: 2, c: 3 };
Or with the questions sample:
const myObject = {"ircEvent": "PRIVMSG", "method": "newURI", "regex": "^http://.*"};
const { regex, ...newObject } = myObject;
console.log(newObject);
You can see it in action in the Babel try-out editor.
Edit:
To reassign to the same variable, use a let:
let myObject = {"ircEvent": "PRIVMSG", "method": "newURI", "regex": "^http://.*"};
({ regex, ...myObject } = myObject);
console.log(myObject);
var myObject = {"ircEvent": "PRIVMSG", "method": "newURI", "regex": "^http://.*"};
delete myObject.regex;
console.log ( myObject.regex); // logs: undefined
This works in Firefox and Internet Explorer, and I think it works in all others.
The delete operator is used to remove properties from objects.
const obj = { foo: "bar" };
delete obj.foo;
obj.hasOwnProperty("foo"); // false
Note that, for arrays, this is not the same as removing an element. To remove an element from an array, use Array#splice or Array#pop. For example:
arr; // [0, 1, 2, 3, 4]
arr.splice(3,1); // 3
arr; // [0, 1, 2, 4]
Details
Strictly speaking, it's impossible to truly delete anything in JavaScript. The delete operator neither deletes objects nor frees memory. Rather, it sets its operand to undefined and manipulates the parent object so that the member is gone.
let parent = {
member: { str: "Hello" }
};
let secondref = parent.member;
delete parent.member;
parent.member; // undefined
secondref; // { str: "Hello" }
The object is not deleted. Only the reference is. Memory is only freed
by the garbage collector when all references to an object are removed.
Another important caveat is that the delete operator will not reorganize structures for you, which has results that can seem counterintuitive. Deleting an array index, for example, will leave a "hole" in it.
let array = [0, 1, 2, 3]; // [0, 1, 2, 3]
delete array[2]; // [0, 1, empty, 3]
This is because arrays are objects. So indices are the same as keys.
let fauxarray = {0: 1, 1: 2, length: 2};
fauxarray.__proto__ = [].__proto__;
fauxarray.push(3);
fauxarray; // [1, 2, 3]
Array.isArray(fauxarray); // false
Array.isArray([1, 2, 3]); // true
Different built-in functions in JavaScript handle arrays with holes in them differently.
for..in statements will skip the empty index completely.
A naive for loop will yield undefined for the value at the index.
Any method using Symbol.iterator will return undefined for the value at the index.
forEach, map and reduce will simply skip the missing index, but will not remove it
Example:
let array = [1, 2, 3]; // [1,2,3]
delete array[1]; // [1, empty, 3]
array.map(x => 0); // [0, empty, 0]
So, the delete operator should not be used for the common use-case of removing elements from an array. Arrays have a dedicated methods for removing elements and reallocating memory: Array#splice() and Array#pop.
Array#splice(start[, deleteCount[, item1[, item2[, ...]]]])
Array#splice mutates the array, and returns any removed indices. deleteCount elements are removed from index start, and item1, item2... itemN are inserted into the array from index start. If deleteCount is omitted then elements from startIndex are removed to the end of the array.
let a = [0,1,2,3,4]
a.splice(2,2) // returns the removed elements [2,3]
// ...and `a` is now [0,1,4]
There is also a similarly named, but different, function on Array.prototype: Array#slice.
Array#slice([begin[, end]])
Array#slice is non-destructive, and returns a new array containing the indicated indices from start to end. If end is left unspecified, it defaults to the end of the array. If end is positive, it specifies the zero-based non-inclusive index to stop at. If end is negative it, it specifies the index to stop at by counting back from the end of the array (eg. -1 will omit the final index). If end <= start, the result is an empty array.
let a = [0,1,2,3,4]
let slices = [
a.slice(0,2),
a.slice(2,2),
a.slice(2,3),
a.slice(2,5) ]
// a [0,1,2,3,4]
// slices[0] [0 1]- - -
// slices[1] - - - - -
// slices[2] - -[3]- -
// slices[3] - -[2 4 5]
Array#pop
Array#pop removes the last element from an array, and returns that element. This operation changes the length of the array. The opposite operation is push
Array#shift
Array#shift is similar to pop, except it removes the first element. The opposite operation is unshift.
Spread Syntax (ES6)
To complete Koen's answer, in case you want to remove a dynamic variable using the spread syntax, you can do it like so:
const key = 'a';
const { [key]: foo, ...rest } = { a: 1, b: 2, c: 3 };
console.log(foo); // 1
console.log(rest); // { b: 2, c: 3 }
* foo will be a new variable with the value of a (which is 1).
Extended answer 😇
There are a few common ways to remove a property from an object. Each one has its own pros and cons (check this performance comparison):
Delete Operator
It is readable and short, however, it might not be the best choice if you are operating on a large number of objects as its performance is not optimized.
delete obj[key];
Reassignment
It is more than two times faster than delete, however the property is not deleted and can be iterated.
obj[key] = null;
obj[key] = false;
obj[key] = undefined;
Spread Operator
This ES6 operator allows us to return a brand new object, excluding any properties, without mutating the existing object. The downside is that it has the worse performance out of the above and is not suggested to be used when you need to remove many properties at a time.
{ [key]: val, ...rest } = obj;
Another alternative is to use the Underscore.js library.
Note that _.pick() and _.omit() both return a copy of the object and don't directly modify the original object. Assigning the result to the original object should do the trick (not shown).
Reference: link _.pick(object, *keys)
Return a copy of the object, filtered to only have values for the
whitelisted keys (or array of valid keys).
var myJSONObject =
{"ircEvent": "PRIVMSG", "method": "newURI", "regex": "^http://.*"};
_.pick(myJSONObject, "ircEvent", "method");
=> {"ircEvent": "PRIVMSG", "method": "newURI"};
Reference: link _.omit(object, *keys)
Return a copy of the object, filtered to omit the
blacklisted keys (or array of keys).
var myJSONObject =
{"ircEvent": "PRIVMSG", "method": "newURI", "regex": "^http://.*"};
_.omit(myJSONObject, "regex");
=> {"ircEvent": "PRIVMSG", "method": "newURI"};
For arrays, _.filter() and _.reject() can be used in a similar manner.
To clone an object without a property:
For example:
let object = { a: 1, b: 2, c: 3 };
And we need to delete a.
With an explicit prop key:
const { a, ...rest } = object;
object = rest;
With a variable prop key:
const propKey = 'a';
const { [propKey]: propValue, ...rest } = object;
object = rest;
A cool arrow function 😎:
const removeProperty = (propKey, { [propKey]: propValue, ...rest }) => rest;
object = removeProperty('a', object);
For multiple properties
const removeProperties = (object, ...keys) => (keys.length ? removeProperties(removeProperty(keys.pop(), object), ...keys) : object);
Usage
object = removeProperties(object, 'a', 'b') // result => { c: 3 }
Or
const propsToRemove = ['a', 'b']
object = removeProperties(object, ...propsToRemove) // result => { c: 3 }
The term you have used in your question title, Remove a property from a JavaScript object, can be interpreted in some different ways. The one is to remove it for whole the memory and the list of object keys or the other is just to remove it from your object. As it has been mentioned in some other answers, the delete keyword is the main part. Let's say you have your object like:
myJSONObject = {"ircEvent": "PRIVMSG", "method": "newURI", "regex": "^http://.*"};
If you do:
console.log(Object.keys(myJSONObject));
the result would be:
["ircEvent", "method", "regex"]
You can delete that specific key from your object keys like:
delete myJSONObject["regex"];
Then your objects key using Object.keys(myJSONObject) would be:
["ircEvent", "method"]
But the point is if you care about memory and you want to whole the object gets removed from the memory, it is recommended to set it to null before you delete the key:
myJSONObject["regex"] = null;
delete myJSONObject["regex"];
The other important point here is to be careful about your other references to the same object. For instance, if you create a variable like:
var regex = myJSONObject["regex"];
Or add it as a new pointer to another object like:
var myOtherObject = {};
myOtherObject["regex"] = myJSONObject["regex"];
Then even if you remove it from your object myJSONObject, that specific object won't get deleted from the memory, since the regex variable and myOtherObject["regex"] still have their values. Then how could we remove the object from the memory for sure?
The answer would be to delete all the references you have in your code, pointed to that very object and also not use var statements to create new references to that object. This last point regarding var statements, is one of the most crucial issues that we are usually faced with, because using var statements would prevent the created object from getting removed.
Which means in this case you won't be able to remove that object because you have created the regex variable via a var statement, and if you do:
delete regex; //False
The result would be false, which means that your delete statement haven't been executed as you expected. But if you had not created that variable before, and you only had myOtherObject["regex"] as your last existing reference, you could have done this just by removing it like:
myOtherObject["regex"] = null;
delete myOtherObject["regex"];
In other words, a JavaScript object is eligible to be killed as soon as there is no reference left in your code pointed to that object.
Update:
Thanks to #AgentME:
Setting a property to null before deleting it doesn't accomplish
anything (unless the object has been sealed by Object.seal and the
delete fails. That's not usually the case unless you specifically
try).
To get more information on Object.seal: Object.seal()
ECMAScript 2015 (or ES6) came with built-in Reflect object. It is possible to delete object property by calling Reflect.deleteProperty() function with target object and property key as parameters:
Reflect.deleteProperty(myJSONObject, 'regex');
which is equivalent to:
delete myJSONObject['regex'];
But if the property of the object is not configurable it cannot be deleted neither with deleteProperty function nor delete operator:
let obj = Object.freeze({ prop: "value" });
let success = Reflect.deleteProperty(obj, "prop");
console.log(success); // false
console.log(obj.prop); // value
Object.freeze() makes all properties of object not configurable (besides other things). deleteProperty function (as well as delete operator) returns false when tries to delete any of it's properties. If property is configurable it returns true, even if property does not exist.
The difference between delete and deleteProperty is when using strict mode:
"use strict";
let obj = Object.freeze({ prop: "value" });
Reflect.deleteProperty(obj, "prop"); // false
delete obj["prop"];
// TypeError: property "prop" is non-configurable and can't be deleted
Suppose you have an object that looks like this:
var Hogwarts = {
staff : [
'Argus Filch',
'Filius Flitwick',
'Gilderoy Lockhart',
'Minerva McGonagall',
'Poppy Pomfrey',
...
],
students : [
'Hannah Abbott',
'Katie Bell',
'Susan Bones',
'Terry Boot',
'Lavender Brown',
...
]
};
Deleting an object property
If you want to use the entire staff array, the proper way to do this, would be to do this:
delete Hogwarts.staff;
Alternatively, you could also do this:
delete Hogwarts['staff'];
Similarly, removing the entire students array would be done by calling delete Hogwarts.students; or delete Hogwarts['students'];.
Deleting an array index
Now, if you want to remove a single staff member or student, the procedure is a bit different, because both properties are arrays themselves.
If you know the index of your staff member, you could simply do this:
Hogwarts.staff.splice(3, 1);
If you do not know the index, you'll also have to do an index search:
Hogwarts.staff.splice(Hogwarts.staff.indexOf('Minerva McGonnagall') - 1, 1);
Note
While you technically can use delete for an array, using it would result in getting incorrect results when calling for example Hogwarts.staff.length later on. In other words, delete would remove the element, but it wouldn't update the value of length property. Using delete would also mess up your indexing.
So, when deleting values from an object, always first consider whether you're dealing with object properties or whether you're dealing with array values, and choose the appropriate strategy based on that.
If you want to experiment with this, you can use this Fiddle as a starting point.
I personally use Underscore.js or Lodash for object and array manipulation:
myObject = _.omit(myObject, 'regex');
Using delete method is the best way to do that, as per MDN description, the delete operator removes a property from an object. So you can simply write:
delete myObject.regex;
// OR
delete myObject['regex'];
The delete operator removes a given property from an object. On
successful deletion, it will return true, else false will be returned.
However, it is important to consider the following scenarios:
If the property which you are trying to delete does not exist, delete
will not have any effect and will return true
If a property with the same name exists on the object's prototype
chain, then, after deletion, the object will use the property from the
prototype chain (in other words, delete only has an effect on own
properties).
Any property declared with var cannot be deleted from the global scope
or from a function's scope.
As such, delete cannot delete any functions in the global scope (whether this is part of a function definition or a function (expression).
Functions which are part of an object (apart from the
global scope) can be deleted with delete.
Any property declared with let or const cannot be deleted from the scope within which they were defined. Non-configurable properties cannot be removed. This includes properties of built-in objects like Math, Array, Object and properties that are created as non-configurable with methods like Object.defineProperty().
The following snippet gives another simple example:
var Employee = {
age: 28,
name: 'Alireza',
designation: 'developer'
}
console.log(delete Employee.name); // returns true
console.log(delete Employee.age); // returns true
// When trying to delete a property that does
// not exist, true is returned
console.log(delete Employee.salary); // returns true
For more info about and seeing more examples visit the link below:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/delete
Another solution, using Array#reduce.
var myObject = {
"ircEvent": "PRIVMSG",
"method": "newURI",
"regex": "^http://.*"
};
myObject = Object.keys(myObject).reduce(function(obj, key) {
if (key != "regex") { //key you want to remove
obj[key] = myObject[key];
}
return obj;
}, {});
console.log(myObject);
However, it will mutate the original object. If you want to create a new object without the specified key, just assign the reduce function to a new variable, e.g.:
(ES6)
const myObject = {
ircEvent: 'PRIVMSG',
method: 'newURI',
regex: '^http://.*',
};
const myNewObject = Object.keys(myObject).reduce((obj, key) => {
key !== 'regex' ? obj[key] = myObject[key] : null;
return obj;
}, {});
console.log(myNewObject);
There are a lot of good answers here but I just want to chime in that when using delete to remove a property in JavaScript, it is often wise to first check if that property exists to prevent errors.
E.g
var obj = {"property":"value", "property2":"value"};
if (obj && obj.hasOwnProperty("property2")) {
delete obj.property2;
} else {
//error handling
}
Due to the dynamic nature of JavaScript there are often cases where you simply don't know if the property exists or not. Checking if obj exists before the && also makes sure you don't throw an error due to calling the hasOwnProperty() function on an undefined object.
Sorry if this didn't add to your specific use case but I believe this to be a good design to adapt when managing objects and their properties.
This post is very old and I find it very helpful so I decided to share the unset function I wrote in case someone else see this post and think why it's not so simple as it in PHP unset function.
The reason for writing this new unset function, is to keep the index of all other variables in this hash_map. Look at the following example, and see how the index of "test2" did not change after removing a value from the hash_map.
function unset(unsetKey, unsetArr, resort) {
var tempArr = unsetArr;
var unsetArr = {};
delete tempArr[unsetKey];
if (resort) {
j = -1;
}
for (i in tempArr) {
if (typeof(tempArr[i]) !== 'undefined') {
if (resort) {
j++;
} else {
j = i;
}
unsetArr[j] = tempArr[i];
}
}
return unsetArr;
}
var unsetArr = ['test', 'deletedString', 'test2'];
console.log(unset('1', unsetArr, true)); // output Object {0: "test", 1: "test2"}
console.log(unset('1', unsetArr, false)); // output Object {0: "test", 2: "test2"}
There are a couple of ways to remove properties from an object:
1) Remove using a dot property accessor (mutable)
const myObject = {
"ircEvent": "PRIVMSG",
"method": "newURI",
"regex": "^http://.*",
};
delete myObject.regex;
console.log(myObject);
2. Remove using square brackets property accessor (mutable)
const myObject = {
"ircEvent": "PRIVMSG",
"method": "newURI",
"regex": "^http://.*",
};
delete myObject['regex'];
console.log(myObject);
// or
const name = 'ircEvent';
delete myObject[name];
console.log(myObject);
3) Alternative option but without altering the original object, is using object destructuring and rest syntax (immutable)
const myObject = {
"ircEvent": "PRIVMSG",
"method": "newURI",
"regex": "^http://.*",
};
const { regex, ...myObjectRest} = myObject;
console.log(myObjectRest);
Using ramda#dissoc you will get a new object without the attribute regex:
const newObject = R.dissoc('regex', myObject);
// newObject !== myObject
You can also use other functions to achieve the same effect - omit, pick, ...
Try the following method. Assign the Object property value to undefined. Then stringify the object and parse.
var myObject = {"ircEvent": "PRIVMSG", "method": "newURI", "regex": "^http://.*"};
myObject.regex = undefined;
myObject = JSON.parse(JSON.stringify(myObject));
console.log(myObject);
Using Lodash
import omit from 'lodash/omit';
const prevObject = {test: false, test2: true};
// Removes test2 key from previous object
const nextObject = omit(prevObject, 'test2');
Using Ramda
R.omit(['a', 'd'], {a: 1, b: 2, c: 3, d: 4}); //=> {b: 2, c: 3}
If you want to delete a property deeply nested in the object then you can use the following recursive function with path to the property as the second argument:
var deepObjectRemove = function(obj, path_to_key){
if(path_to_key.length === 1){
delete obj[path_to_key[0]];
return true;
}else{
if(obj[path_to_key[0]])
return deepObjectRemove(obj[path_to_key[0]], path_to_key.slice(1));
else
return false;
}
};
Example:
var a = {
level1:{
level2:{
level3: {
level4: "yolo"
}
}
}
};
deepObjectRemove(a, ["level1", "level2", "level3"]);
console.log(a);
//Prints {level1: {level2: {}}}
Object.assign() & Object.keys() & Array.map()
const obj = {
"Filters":[
{
"FilterType":"between",
"Field":"BasicInformationRow.A0",
"MaxValue":"2017-10-01",
"MinValue":"2017-09-01",
"Value":"Filters value"
}
]
};
let new_obj1 = Object.assign({}, obj.Filters[0]);
let new_obj2 = Object.assign({}, obj.Filters[0]);
/*
// old version
let shaped_obj1 = Object.keys(new_obj1).map(
(key, index) => {
switch (key) {
case "MaxValue":
delete new_obj1["MaxValue"];
break;
case "MinValue":
delete new_obj1["MinValue"];
break;
}
return new_obj1;
}
)[0];
let shaped_obj2 = Object.keys(new_obj2).map(
(key, index) => {
if(key === "Value"){
delete new_obj2["Value"];
}
return new_obj2;
}
)[0];
*/
// new version!
let shaped_obj1 = Object.keys(new_obj1).forEach(
(key, index) => {
switch (key) {
case "MaxValue":
delete new_obj1["MaxValue"];
break;
case "MinValue":
delete new_obj1["MinValue"];
break;
default:
break;
}
}
);
let shaped_obj2 = Object.keys(new_obj2).forEach(
(key, index) => {
if(key === "Value"){
delete new_obj2["Value"];
}
}
);
Dan's assertion that 'delete' is very slow and the benchmark he posted were doubted. So I carried out the test myself in Chrome 59. It does seem that 'delete' is about 30 times slower:
var iterationsTotal = 10000000; // 10 million
var o;
var t1 = Date.now(),t2;
for (let i=0; i<iterationsTotal; i++) {
o = {a:1,b:2,c:3,d:4,e:5};
delete o.a; delete o.b; delete o.c; delete o.d; delete o.e;
}
console.log ((t2=Date.now())-t1); // 6135
for (let i=0; i<iterationsTotal; i++) {
o = {a:1,b:2,c:3,d:4,e:5};
o.a = o.b = o.c = o.d = o.e = undefined;
}
console.log (Date.now()-t2); // 205
Note that I purposely carried out more than one 'delete' operations in one loop cycle to minimize the effect caused by the other operations.
Property Removal in JavaScript
There are many different options presented on this page, not because most of the options are wrong—or because the answers are duplicates—but because the appropriate technique depends on the situation you're in and the goals of the tasks you and/or you team are trying to fulfill. To answer you question unequivocally, one needs to know:
The version of ECMAScript you're targeting
The range of object types you want to remove properties on and the type of property names you need to be able to omit (Strings only? Symbols? Weak references mapped from arbitrary objects? These have all been types of property pointers in JavaScript for years now)
The programming ethos/patterns you and your team use. Do you favor functional approaches and mutation is verboten on your team, or do you employ wild west mutative object-oriented techniques?
Are you looking to achieve this in pure JavaScript or are you willing & able to use a 3rd-party library?
Once those four queries have been answered, there are essentially four categories of "property removal" in JavaScript to chose from in order to meet your goals. They are:
Mutative object property deletion, unsafe
This category is for operating on object literals or object instances when you want to retain/continue to use the original reference and aren't using stateless functional principles in your code. An example piece of syntax in this category:
'use strict'
const iLikeMutatingStuffDontI = { myNameIs: 'KIDDDDD!', [Symbol.for('amICool')]: true }
delete iLikeMutatingStuffDontI[Symbol.for('amICool')] // true
Object.defineProperty({ myNameIs: 'KIDDDDD!', 'amICool', { value: true, configurable: false })
delete iLikeMutatingStuffDontI['amICool'] // throws
This category is the oldest, most straightforward & most widely supported category of property removal. It supports Symbol & array indexes in addition to strings and works in every version of JavaScript except for the very first release. However, it's mutative which violates some programming principles and has performance implications. It also can result in uncaught exceptions when used on non-configurable properties in strict mode.
Rest-based string property omission
This category is for operating on plain object or array instances in newer ECMAScript flavors when a non-mutative approach is desired and you don't need to account for Symbol keys:
const foo = { name: 'KIDDDDD!', [Symbol.for('isCool')]: true }
const { name, ...coolio } = foo // coolio doesn't have "name"
const { isCool, ...coolio2 } = foo // coolio2 has everything from `foo` because `isCool` doesn't account for Symbols :(
Mutative object property deletion, safe
This category is for operating on object literals or object instances when you want to retain/continue to use the original reference while guarding against exceptions being thrown on unconfigurable properties:
'use strict'
const iLikeMutatingStuffDontI = { myNameIs: 'KIDDDDD!', [Symbol.for('amICool')]: true }
Reflect.deleteProperty(iLikeMutatingStuffDontI, Symbol.for('amICool')) // true
Object.defineProperty({ myNameIs: 'KIDDDDD!', 'amICool', { value: true, configurable: false })
Reflect.deleteProperty(iLikeMutatingStuffDontI, 'amICool') // false
In addition, while mutating objects in-place isn't stateless, you can use the functional nature of Reflect.deleteProperty to do partial application and other functional techniques that aren't possible with delete statements.
Syntax-based string property omission
This category is for operating on plain object or array instances in newer ECMAScript flavors when a non-mutative approach is desired and you don't need to account for Symbol keys:
const foo = { name: 'KIDDDDD!', [Symbol.for('isCool')]: true }
const { name, ...coolio } = foo // coolio doesn't have "name"
const { isCool, ...coolio2 } = foo // coolio2 has everything from `foo` because `isCool` doesn't account for Symbols :(
Library-based property omission
This category is generally allows for greater functional flexibility, including accounting for Symbols & omitting more than one property in one statement:
const o = require("lodash.omit")
const foo = { [Symbol.for('a')]: 'abc', b: 'b', c: 'c' }
const bar = o(foo, 'a') // "'a' undefined"
const baz = o(foo, [ Symbol.for('a'), 'b' ]) // Symbol supported, more than one prop at a time, "Symbol.for('a') undefined"
Here's an ES6 way to remove the entry easily:
let myObject = {
"ircEvent": "PRIVMSG",
"method": "newURI",
"regex": "^http://.*"
};
const removeItem = 'regex';
const { [removeItem]: remove, ...rest } = myObject;
console.log(remove); // "^http://.*"
console.log(rest); // Object { ircEvent: "PRIVMSG", method: "newURI" }
#johnstock, we can also use JavaScript's prototyping concept to add method to objects to delete any passed key available in calling object.
Above answers are appreciated.
var myObject = {
"ircEvent": "PRIVMSG",
"method": "newURI",
"regex": "^http://.*"
};
// 1st and direct way
delete myObject.regex; // delete myObject["regex"]
console.log(myObject); // { ircEvent: 'PRIVMSG', method: 'newURI' }
// 2 way - by using the concept of JavaScript's prototyping concept
Object.prototype.removeFromObjectByKey = function(key) {
// If key exists, remove it and return true
if (this[key] !== undefined) {
delete this[key]
return true;
}
// Else return false
return false;
}
var isRemoved = myObject.removeFromObjectByKey('method')
console.log(myObject) // { ircEvent: 'PRIVMSG' }
// More examples
var obj = {
a: 45,
b: 56,
c: 67
}
console.log(obj) // { a: 45, b: 56, c: 67 }
// Remove key 'a' from obj
isRemoved = obj.removeFromObjectByKey('a')
console.log(isRemoved); //true
console.log(obj); // { b: 56, c: 67 }
// Remove key 'd' from obj which doesn't exist
var isRemoved = obj.removeFromObjectByKey('d')
console.log(isRemoved); // false
console.log(obj); // { b: 56, c: 67 }
You can use a filter like below
var myObject = {
"ircEvent": "PRIVMSG",
"method": "newURI",
"regex": "^http://.*"
};
// Way 1
let filter1 = {}
Object.keys({...myObject}).filter(d => {
if(d !== 'regex'){
filter1[d] = myObject[d];
}
})
console.log(filter1)
// Way 2
let filter2 = Object.fromEntries(Object.entries({...myObject}).filter(d =>
d[0] !== 'regex'
))
console.log(filter2)
I have used Lodash "unset" to make it happen for a nested object also... only this needs to write small logic to get the path of the property key which is expected by the omit method.
Method which returns the property path as an array
var a = {"bool":{"must":[{"range":{"price_index.final_price":{"gt":"450", "lt":"500"}}}, {"bool":{"should":[{"term":{"color_value.keyword":"Black"}}]}}]}};
function getPathOfKey(object,key,currentPath, t){
var currentPath = currentPath || [];
for(var i in object){
if(i == key){
t = currentPath;
}
else if(typeof object[i] == "object"){
currentPath.push(i)
return getPathOfKey(object[i], key,currentPath)
}
}
t.push(key);
return t;
}
document.getElementById("output").innerHTML =JSON.stringify(getPathOfKey(a,"price_index.final_price"))
<div id="output">
</div>
Then just using Lodash unset method remove property from object.
var unset = require('lodash.unset');
unset(a, getPathOfKey(a, "price_index.final_price"));
let myObject = {
"ircEvent": "PRIVMSG",
"method": "newURI",
"regex": "^http://.*"
};
obj = Object.fromEntries(
Object.entries(myObject).filter(function (m){
return m[0] != "regex"/*or whatever key to delete*/
}
))
console.log(obj)
You can also just treat the object like a2d array using Object.entries, and use splice to remove an element as you would in a normal array, or simply filter through the object, as one would an array, and assign the reconstructed object back to the original variable
If you don't want to modify the original object.
Remove a property without mutating the object
If mutability is a concern, you can create a completely new object by copying all the properties from the old, except the one you want to remove.
let myObject = {
"ircEvent": "PRIVMSG",
"method": "newURI",
"regex": "^http://.*"
};
let prop = 'regex';
const updatedObject = Object.keys(myObject).reduce((object, key) => {
if (key !== prop) {
object[key] = myObject[key]
}
return object
}, {})
console.log(updatedObject);