I'm making a dictionary of words, so there are 1,000,000+ words.
The problem comes when I need to store the word constructor. I know this is a reserved word in javascript, but I need to add it to the dictionary.
var dictionary = {}
console.log(dictionary ['word_1'])
//undefined, this is good
console.log(dictionary ['word_2'])
//undefined, this is good
console.log(dictionary ['constructor'])
//[Function: Object]
// this cause initialization code to break
How can I fix this? I could muck with the it like key=key+"_" but that seems bad. Is there anything else I can do?
Instead of using a JS object, you could use the built-in Map type which uses strings/symbols as keys and does not conflict with any existing properties.
Replace
var dictionary = {} with var dictionary = new Map()
Override the constructor key as undefined
According to the MDN Object.prototype page, the only thing that isn't hidden by the __fieldname__ schema is the "constructor field". Thus, you could just initialize your objects via { 'constructor': undefined }.
However, you would have to make sure that in your for .. in statements would filter out all keys with undefined as their value, as it would pick up constructor as a "valid" key (even though it wouldn't before you specifically set it to undefined). I.E.
for(var key in obj) if(obj[key] !== undefined) { /* do things */ }
Check for types when getting/setting
Otherwise, you could just check the type when you 'fetch' or 'store' it. I.E.
function get(obj, key) {
if(typeof obj[key] !== 'function') // optionally, `&& typeof obj[key] !== 'object')`
return obj[key];
else
return undefined;
}
I think you should store all words and translation of them in an array. When you need to translate a word, you can use find method of Array.
For example:
var dict = [
{ word: "abc", translated: "xyz" },
...
];
Then:
var searching_word = "abc";
var translation = dict.find(function (item) {
return item.word == searching_word;
});
console.log(translation.translated);
// --> xyz
To achieve expected result , use below option of using index to get value of any key value
var dictionary = {};
var dictionary1 = {
constructor: "test"
};
//simple function to get key value using index
function getVal(obj, val) {
var keys = Object.keys(obj);
var index = keys.indexOf(val);//get index of key, in our case -contructor
return obj[keys[index]]; // return value using indec of that key
}
console.log(getVal(dictionary, "constructor"));//undefined as expected
console.log(getVal(dictionary1, "constructor"));//test
console.log(dictionary["word_1"]);
//undefined, this is good
console.log(dictionary["word_2"]);
//undefined, this is good
codepen - https://codepen.io/nagasai/pen/LOEGxM
For testing , I gave one object with key-constructor and other object without constructor.
Basically I am getting the index of key first and getting value using index
Related
Is it possible to console.log something like this:
myParent.myChildData(5)
(variable literal name + value in brackets)
from a JSON object such as this:
{myParent: {myChildData: 5}}
I would like to do it with referencing the object notation ideally only once. Something like:
console.log(printExpression(myParent.myChildData))
Where printExpression I'm certainly happy to be a generic helper function that could return this. I've searched high and low, but obviously printExpression receives the actual evaluated value and this causes a road block.
You can turn JSON into a JavaScript object by using JSON.parse(jsonString).
You can store that as a variable and then console.log it.
Or you can just directly console.log the passed data like this:
console.log(JSON.parse('{"myparent":{"myChildData": 5}}').myParent.myChildData);
Edit
After understanding what exactly the helper function does, I've created a printExpression function that returns string values based on your example.
function printExpression(object, stringBefore) {
//Recursively make objects with keys as methods
let newObject = {};
for (var key in object) {
//Make sure the key exists on the object
if (object.hasOwnProperty(key)) {
let value = object[key];
//If the value is an object, just add a get method that returns the object
if (typeof(value) == "object") {
let childObject = printExpression(value, key + ".");
newObject[key] = childObject;
}
//If not, make a method that returns the wanted syntax
else {
//Form the string based on specific syntax
let str = key + "(" + value + ")";
//Check if we should add stringBefore
if (stringBefore) {
str = stringBefore + str;
}
newObject[key] = str;
}
}
}
//Return the new object
return newObject;
}
var example = printExpression(JSON.parse('{"myParent": {"myChildData": 5}}'));
console.log(example.myParent.myChildData);
How It Works
When creating the helper object, it recursively reads all the keys of the original object and makes a new object that returns the keys in an organized way. For example if the original object was { greeting: "hello" } then newObject.greeting would be "greeting(hello)" (as you said it should be).
Possible Problems
Doesn't get updated when you change the original object. I don't think this will be much of a problem as you seem to be reading static JSON data, but just letting you know.
I want to create data structure like that.
Var ans =[{"b":[1,2]},{"g":[100,2]}]
I want to create a new object within list if key not exists in list ans.
Else if key exists in one object of ans list then I want to add new values into the object of ans list
For Example:
Example 1) new data c:{2000}
then
Var ans =[{"b":[1,2]},{"g":[100,2]},{c:[2000]}]
Example 2) new data g:{50}
then
Var ans =[{"b":[1,2]},{"g":[100,2,500]},{c:[2000]}]
I am a beginner in node js, understand array, object concept, but not getting exact logic!
Thanks!
You can try following:
Logic
Filter array based on key
Check if object with mentioned key exists or not.
If yes, push value to this array.
If not, create a dummy object and push this object to original array.
Correction, when you do .push({key: value}), key will be considered as string.
Alternates
If you are using ES6, .push({ [key] : value })
Create a dummy object var o = {}. Set key and value to it o[key] = value and push this object.
Optimisations
Instead of setting value like obj[key] = value, since we will be operating on arrays, try obj[key] = [].concat(value). This will enable you to pass value as number or array of values.
Instead of checking the existence of value in .filter, try Array.isArray to check if value exists and is of type array.
Custom function
function checkAndPush(array, key, value) {
var filteredList = array.filter(function(o) {
return Array.isArray(o[key]);
});
filteredList.length > 0 ? filteredList[0][key].push(value) : array.push({
[key]: [].concat(value)
});
return array;
}
var ans =[{"b":[1,2]},{"g":[100,2]}]
console.log(checkAndPush(ans, "c", [2,3]))
console.log(checkAndPush(ans, "c", 4));
Prototype function
Array.prototype.checkAndPush = function(key, value) {
var filteredList = this.filter(function(o) {
return Array.isArray(o[key]);
});
var dummy = {}
dummy[key] = [].concat(value)
filteredList.length > 0 ? filteredList[0][key].push(value) : this.push(dummy);
// or ES6: this.push({ [key]: [].concat(value) })
return this;
}
var ans =[{"b":[1,2]},{"g":[100,2]}]
console.log(ans.checkAndPush("c", [2,3]))
console.log(ans.checkAndPush("c", 4));
If you are dealing with objects as your values
ans[key] = ans[key] || []
ans[key].push(value)
Note, this works because your values will be an array. If they could be primatives then you would use hasOwnProperty to check.
if (ans.hasOwnProperty(key)) {
// Add this to your key somehow
} else {
// initialize the key with your value
}
Node.js is nothing but a library built on javascript. You can do anything using javascript type of progmming. However push and pop method should be able to help you to deal with nodejs array.
ans[key].push(value)
I have an object named Object1 which is third party object & I'm putting in properties inside it.
Object1.shoot({
'prop1':prop_1,
'prop2':prop_2,
'prop3':prop_3
});
Now I want the key 'prop1' to be added as property to Object1 only when prop_1 has some value. Otherwise I do not want to add it,
Whats the best way to do it?
You can check each property in for loop first.
var params = {
'prop1':prop_1,
'prop2':prop_2,
'prop3':prop_3
};
for (var param in params) {
if (typeof params[param] === 'undefined') {
delete params[param];
}
}
Object1.shoot(params);
You can make a helper function to add the property if defined:
function addProp(target, name, value) {
if(value != null) {
target[name] = value
}
}
var props = {}
addProp(props, 'prop1', prop_1)
addProp(props, 'prop2', prop_2)
addProp(props, 'prop3', prop_3)
The above does a null check instead of an undefined check. You can change as appropriate (e.g. you might not want empty strings, or number zero or anything else), though check this first:
How to determine if variable is 'undefined' or 'null'?
var Items = {
FormVariables: function()
{
if (this.array === 'undefined')
{
this.array = [];
}
return this.array;
}
};
This was my attempt at it and I get an error of it being undefined. Can I even have variables within Items scope like I am attempting. If so, what does the syntax look like?
I am only asking if this can be done using the var variableName = {} syntax.
EDIT:
Accessing it
var formVars = new Array();
formVars.push('[');
for (var item in gd["FormVariables"])
{
formVars.push('"' + item + '":"' + gd["FormVariables"][item] + '"');
}
formVars.push(']');
The real goal here is to take all these items and convert it to a JSON array of key/value pairs
Yes, you can use []. [] is a shortcut for new Array, just like {} is for new Object.
this.array = [];
By the way, there are no 'compiler errors' since JavaScript is not a compiled language but an interpreted one.
Also, your checking does not make much sense. You'd probably want:
if (typeof this.array === 'undefined')
since typeof returns a string. Checking for the string 'undefined' is not the same as checking for 'real' undefined. For the string, it must have been set explicitly to those characters, which is almost never the case.
I've got an array
var assoc_pagine = new Array();
assoc_pagine["home"]=0;
assoc_pagine["about"]=1;
assoc_pagine["work"]=2;
I tried
if (assoc_pagine[var] != "undefined") {
but it doesn't seem to work
I'm using jquery, I don't know if it can help
Thanks
Use the in keyword to test if a attribute is defined in a object
if (assoc_var in assoc_pagine)
OR
if ("home" in assoc_pagine)
There are quite a few issues here.
Firstly, is var supposed to a variable has the value "home", "work" or "about"? Or did you mean to inspect actual property called "var"?
If var is supposed to be a variable that has a string value, please note that var is a reserved word in JavaScript and you will need to use another name, such as assoc_var.
var assoc_var = "home";
assoc_pagine[assoc_var] // equals 0 in your example
If you meant to inspect the property called "var", then you simple need to put it inside of quotes.
assoc_pagine["var"]
Then, undefined is not the same as "undefined". You will need typeof to get the string representation of the objects type.
This is a breakdown of all the steps.
var assoc_var = "home";
var value = assoc_pagine[assoc_var]; // 0
var typeofValue = typeof value; // "number"
So to fix your problem
if (typeof assoc_pagine[assoc_var] != "undefined")
update: As other answers have indicated, using a array is not the best sollution for this problem. Consider using a Object instead.
var assoc_pagine = new Object();
assoc_pagine["home"]=0;
assoc_pagine["about"]=1;
assoc_pagine["work"]=2;
var assoc_pagine = new Array();
assoc_pagine["home"]=0;
Don't use an Array for this. Arrays are for numerically-indexed lists. Just use a plain Object ({}).
What you are thinking of with the 'undefined' string is probably this:
if (typeof assoc_pagine[key]!=='undefined')
This is (more or less) the same as saying
if (assoc_pagine[key]!==undefined)
However, either way this is a bit ugly. You're dereferencing a key that may not exist (which would be an error in any more sensible language), and relying on JavaScript's weird hack of giving you the special undefined value for non-existent properties.
This also doesn't quite tell you if the property really wasn't there, or if it was there but explicitly set to the undefined value.
This is a more explicit, readable and IMO all-round better approach:
if (key in assoc_pagine)
var is a statement... so it's a reserved word... So just call it another way.
And that's a better way of doing it (=== is better than ==)
if(typeof array[name] !== 'undefined') {
alert("Has var");
} else {
alert("Doesn't have var");
}
This is not an Array.
Better declare it like this:
var assoc_pagine = {};
assoc_pagine["home"]=0;
assoc_pagine["about"]=1;
assoc_pagine["work"]=2;
or
var assoc_pagine = {
home:0,
about:1,
work:2
};
To check if an object contains some label you simply do something like this:
if('work' in assoc_pagine){
// do your thing
};
This worked for me
if (assoc_pagine[var] != undefined) {
instead this
if (assoc_pagine[var] != "undefined") {
TLDR; The best I can come up with is this: (Depending on your use case, there are a number of ways to optimize this function.)
function arrayIndexExists(array, index){
if ( typeof index !== 'number' && index === parseInt(index).toString()) {
index = parseInt(index);
} else {
return false;//to avoid checking typeof again
}
return typeof index === 'number' && index % 1===0 && index >= 0 && array.hasOwnKey(index);
}
The other answer's examples get close and will work for some (probably most) purposes, but are technically quite incorrect for reasons I explain below.
Javascript arrays only use 'numerical' keys. When you set an "associative key" on an array, you are actually setting a property on that array object, not an element of that array. For example, this means that the "associative key" will not be iterated over when using Array.forEach() and will not be included when calculating Array.length. (The exception for this is strings like '0' will resolve to an element of the array, but strings like ' 0' won't.)
Additionally, checking array element or object property that doesn't exist does evaluate as undefined, but that doesn't actually tell you that the array element or object property hasn't been set yet. For example, undefined is also the result you get by calling a function that doesn't terminate with a return statement. This could lead to some strange errors and difficulty debugging code.
This can be confusing, but can be explored very easily using your browser's javascript console. (I used chrome, each comment indicates the evaluated value of the line before it.);
var foo = new Array();
foo;
//[]
foo.length;
//0
foo['bar'] = 'bar';
//"bar"
foo;
//[]
foo.length;
//0
foo.bar;
//"bar"
This shows that associative keys are not used to access elements in the array, but for properties of the object.
foo[0] = 0;
//0
foo;
//[0]
foo.length;
//1
foo[2] = undefined
//undefined
typeof foo[2]
//"undefined"
foo.length
//3
This shows that checking typeof doesn't allow you to see if an element has been set.
var foo = new Array();
//undefined
foo;
//[]
foo[0] = 0;
//0
foo['0']
//0
foo[' 0']
//undefined
This shows the exception I mentioned above and why you can't just use parseInt();
If you want to use associative arrays, you are better off using simple objects as other answers have recommended.
if (assoc_pagine.indexOf('home') > -1) {
// we have home element in the assoc_pagine array
}
Mozilla indexOf
function isset(key){
ret = false;
array_example.forEach(function(entry) {
if( entry == key ){
ret = true;
}
});
return ret;
}
alert( isset("key_search") );
The most effective way:
if (array.indexOf(element) > -1) {
alert('Bingooo')
}
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