Add a property to a JavaScript array

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Extending from other answers, here are the following ways of iterating over the array, excluding custom properties.,Arrays are objects and therefore you can add your own properties to them:,Iterating over the array, including all properties (e.g., custom properties, length):,Yes. You can add them to the object by just declaring them and you can also extend Array using Array.prototype


var arr = [1, 2, 3, 4, 5];
arr.prop = 'value';
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Properties are the values associated with a JavaScript object.,JavaScript objects inherit the properties of their prototype. ,Properties are the most important part of any JavaScript object.,A JavaScript object is a collection of unordered properties.

JavaScript Loop

The JavaScript statement loops through the properties of an object.

for... in
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var data = [{
      message: 'This is a test',
      from_user_id: 123,
      to_user_id: 567
   }, {
      message: 'Another test.',
      from_user_id: 123,
      to_user_id: 567
   }, {
      message: 'A third test.',
      from_user_id: '456',
      to_user_id: 567
   groups = Object.create(null),

data.forEach(function(a) {
   groups[a.from_user_id] = groups[a.from_user_id] || [];

result = Object.keys(groups).map(function(k) {
   var temp = {};
   temp[k] = groups[k];
   return temp;


Square bracket array notation similarly allows the triple-dot operator to spread another array into the new array.,Both string and array values contain, in addition to the length property, a number of properties that hold function values.,The push method adds values to the end of an array, and the pop method does the opposite, removing the last value in the array and returning it.,Properties that contain functions are generally called methods of the value they belong to, as in “toUpperCase is a method of a string”.

To run over a list (in listToArray and nth), a for loop specification like this can be used:

for (let node = list; node; node = {}

There’re a few ways to add properties to an object in JavaScript. One way is to add a property using the dot notation:,We added the foo property to the obj object above with value 1.,We can also use the Object.defineProperty function:,We can also add a property by using the bracket notation:

There’re a few ways to add properties to an object in JavaScript. One way is to add a property using the dot notation: = 1;

We can also add a property by using the bracket notation:

obj['foo'] = 1;

So, we can write something like:

obj['foo-bar'] = 1;
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To conditionally add a property to an object, we can make use of the && operator.,In the example above, in the first property definition on obj, the first expression (trueCondition) is true/truthy, so the second expression is returned, and then spread into the object.,Conditionally adding a value to an array looks a little different. Rather than using an && operator, we use a ternary operator.,Spread syntax can be used to expand an iterable (like an array expression), or expand object properties.

.css - 1 baulvz {
   display: inline - block;
const trueCondition = true;
const falseCondition = false;
const obj = {
   ...(trueCondition && {
      dogs: "woof"
   ...(falseCondition && {
      cats: "meow"
}; // { dogs: 'woof' }const arr = [  ...(trueCondition ? ["dog"] : []),  ...(falseCondition ? ["cat"] : [])];// ['dog']
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Object.keys(o) This method returns an array with all the own (not in the prototype chain) enumerable properties' names ("keys") of an object o. , Object.getOwnPropertyNames(o) This method returns an array containing all own properties' names (enumerable or not) of an object o. , loops This method traverses all enumerable properties of an object and its prototype chain. ,The following example creates myHonda with three properties. Note that the engine property is also an object with its own properties.

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One can update the value of the property just by reassigning the value to the same key. ,I have listed few of the ways I know how to add, update and delete the properties. Comment below if you know any other ways.,One can use ES7 Syntax and functional approach and add the property which would yield the same result. ,Here the array method .every is used to iterate through the elements of the array. The property 'responsibility' is reassigned (‘heart of the show to ‘making people laugh’) to different value.

var brooklynNineNine = {
   name: 'Raymond Holt',
   currentRole: 'Captian of brooklyn99',
brooklynNineNine.husband = 'Kevin' // Or brooklynNineNine['husband'] = 'Kevin'

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In order to push an array into the object in JavaScript, we need to utilize the push() function. With the help of Array push function this task is so much easy to achieve. ,How to push an array into the object in JavaScript ?,How to convert two-dimensional array into an object in JavaScript ?,An array can be inserted into the object with push() function, below examples illustrate the above approach:


arr.push(element1[, ...[, elementN]])
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