How to assign value to object in JavaScript?

The Object.assign() method is used to copy the values of all enumerable own properties from one or more source objects to a target object. Objects are assigned and copied by reference. It will return the target object.

Syntax:

Parameter

target: The target object.

sources: The source object(s).

Return value:

This method returns the target object.

Browser Support:

ChromeYesEdgeYesFirefoxYesOperaNo

Example 1

Output:

Example 2

Output:

Example 3

Output:

Object.assign() copies the values (of all enumerable own properties) from one or more source objects to a target object. It has a signature of Object.assign(target, ...sources). The target object is the first parameter and is also used as the return value. Object.assign() is useful for merging objects or cloning them shallowly.

'use strict'; // Merge an object let first = {name: 'Tony'}; let last = {lastName: 'Stark'}; let person = Object.assign(first, last); ChromeSamples.log(person); // {name: 'Tony', lastName: 'Stark'} ChromeSamples.log(first); // first = {name: 'Tony', lastName: 'Stark'} as the target also changed // Merge multiple sources let a = Object.assign({foo: 0}, {bar: 1}, {baz: 2}); ChromeSamples.log(a); // {foo: 0, bar: 1, baz: 2} // Merge and overwrite equal keys let b = Object.assign({foo: 0}, {foo: 1}, {foo: 2}); ChromeSamples.log(b); // {foo: 2} // Clone an object let obj = {person: 'Thor Odinson'}; let clone = Object.assign({}, obj); ChromeSamples.log(clone); // {person: 'Thor Odinson'}

In JavaScript, the let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign(obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30, coder: true } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }7 data type is used to store key value pairs, and like the let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign(obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30, coder: true } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }8 data type, contain many useful methods. These are some useful methods you'll use while working with objects.

Object Assign Method

The let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign(obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30, coder: true } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }9 method is used to

1. add properties and values to an existing object
2. make a new copy of an existing object, or
3. combine multiple existing objects into a single object.

The let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign(obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30, coder: true } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }9 method requires one let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign({}, obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30 } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }1 as a parameter and can accept an unlimited number of let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign({}, obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30 } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }2 as additional parameters.

It's important to note here is that the let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign({}, obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30 } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }1 parameter will always be modified. If that parameter points to an existing object, then that object will be both modified and copied.

If, you wish to create a copy of an object without modifying that original object, you can pass an empty object let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign({}, obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30 } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }4 as the first (let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign({}, obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30 } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }1) parameter and the object to be copied as the second (let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign({}, obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30 } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }6) parameter.

If objects passed as parameters into let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign(obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30, coder: true } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }9 share the same properties (or keys), property values that come later in the parameters list will overwrite those which came earlier.

Syntax

Object.assign(targetObject, ...sourceObject);

Return Value

let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign(obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30, coder: true } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }9 returns the let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign({}, obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30 } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }1.

Examples

Modifying and copying let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign({}, obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30 } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }1:

let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign(obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30, coder: true } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }

Copying let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign({}, obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30 } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }1 without modification:

let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign({}, obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30 } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }

Objects with the same properties:

let obj = {name: 'Dave', age: 30, favoriteColor: 'blue'}; let objCopy = Object.assign({}, obj, {coder: true, favoriteColor: 'red'}); console.log(obj); // { name: 'Dave', age: 30, favoriteColor: 'blue' } console.log(objCopy); // { name: 'Dave', age: 30, favoriteColor: 'red', coder: true }

Object Values Method

The let obj = {name: 'Dave', age: 30, favoriteColor: 'blue'}; let objCopy = Object.assign({}, obj, {coder: true, favoriteColor: 'red'}); console.log(obj); // { name: 'Dave', age: 30, favoriteColor: 'blue' } console.log(objCopy); // { name: 'Dave', age: 30, favoriteColor: 'red', coder: true }2 method takes an object as a parameter and returns an array of its values. This makes it useful for chaining with common let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign(obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30, coder: true } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }8 methods like let obj = {name: 'Dave', age: 30, favoriteColor: 'blue'}; let objCopy = Object.assign({}, obj, {coder: true, favoriteColor: 'red'}); console.log(obj); // { name: 'Dave', age: 30, favoriteColor: 'blue' } console.log(objCopy); // { name: 'Dave', age: 30, favoriteColor: 'red', coder: true }4, let obj = {name: 'Dave', age: 30, favoriteColor: 'blue'}; let objCopy = Object.assign({}, obj, {coder: true, favoriteColor: 'red'}); console.log(obj); // { name: 'Dave', age: 30, favoriteColor: 'blue' } console.log(objCopy); // { name: 'Dave', age: 30, favoriteColor: 'red', coder: true }5, and let obj = {name: 'Dave', age: 30, favoriteColor: 'blue'}; let objCopy = Object.assign({}, obj, {coder: true, favoriteColor: 'red'}); console.log(obj); // { name: 'Dave', age: 30, favoriteColor: 'blue' } console.log(objCopy); // { name: 'Dave', age: 30, favoriteColor: 'red', coder: true }6.

Syntax

Object.values(targetObject);

Return value

An array of the passed object's (let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign({}, obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30 } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }1) values.

Examples

const obj = { firstName: 'Quincy', lastName: 'Larson' } const values = Object.values(obj); console.log(values); // ["Quincy", "Larson"]

If the object you're passing has numbers as keys, then let obj = {name: 'Dave', age: 30, favoriteColor: 'blue'}; let objCopy = Object.assign({}, obj, {coder: true, favoriteColor: 'red'}); console.log(obj); // { name: 'Dave', age: 30, favoriteColor: 'blue' } console.log(objCopy); // { name: 'Dave', age: 30, favoriteColor: 'red', coder: true }8 will return the values according to the numerical order of the keys:

const obj1 = { 0: 'first', 1: 'second', 2: 'third' }; const obj2 = { 100: 'apple', 12: 'banana', 29: 'pear' }; console.log(Object.values(obj1)); // ["first", "second", "third"] console.log(Object.values(obj2)); // ["banana", "pear", "apple"]

If something other than an object is passed to let obj = {name: 'Dave', age: 30, favoriteColor: 'blue'}; let objCopy = Object.assign({}, obj, {coder: true, favoriteColor: 'red'}); console.log(obj); // { name: 'Dave', age: 30, favoriteColor: 'blue' } console.log(objCopy); // { name: 'Dave', age: 30, favoriteColor: 'red', coder: true }2, it will be coerced into an object before being returned as an array:

const str = 'hello'; console.log(Object.values(str)); // ["h", "e", "l", "l", "o"]

Object hasOwnProperty Method

The Object.values(targetObject);0 method returns a boolean indicating if the object owns the specified property.

This is a convenient method to check if an object has the specified property or not since it returns true/false accordingly.

Syntax

Object.values(targetObject);1

Return value

true // or false

Examples

Using Object.values(targetObject);0 to test if a property exist or not in a given object:

const course = { name: 'freeCodeCamp', feature: 'is awesome', } const student = { name: 'enthusiastic student', } course.hasOwnProperty('name'); // returns true course.hasOwnProperty('feature'); // returns true student.hasOwnProperty('name'); // returns true student.hasOwnProperty('feature'); // returns false

Object getOwnPropertyNames Method

The Object.values(targetObject);3 method takes an object as a parameter and returns and array of all its properties.

Syntax

let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign(obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30, coder: true } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }0

Return value

An array of strings of the passed object's properties.

Examples

let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign(obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30, coder: true } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }1

If something other than an object is passed to Object.values(targetObject);3, it will be coerced into an object before being returned as an array:

let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign(obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30, coder: true } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }2

Promise.prototype.then

A Object.values(targetObject);5 function accepts two arguments and returns a Promise.

The first argument is a required function that accepts one argument. Successful fulfillment of a Promise will trigger this function.

The second argument is an optional function that also accepts one argument of its own. A thrown Error or Rejection of a Promise will trigger this function.

let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign(obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30, coder: true } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }3

Object.values(targetObject);5 allows you to perform many asynchronous activities in sequence. You do this by attaching one Object.values(targetObject);7 function to another separated by a dot operator.

let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign(obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30, coder: true } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }4

Map.prototype.entries

Returns a new Object.values(targetObject);8 object that contains the Object.values(targetObject);9 pairs for each element in the const obj = { firstName: 'Quincy', lastName: 'Larson' } const values = Object.values(obj); console.log(values); // ["Quincy", "Larson"]0 object in insertion order.

Syntax

let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign(obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30, coder: true } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }5

Example

let obj = {name: 'Dave', age: 30}; let objCopy = Object.assign(obj, {coder: true}); console.log(obj); // { name: 'Dave', age: 30, coder: true } console.log(objCopy); // { name: 'Dave', age: 30, coder: true }6

More info on objects in JavaScript:

• How to create objects in JavaScript
• How to loop through objects in JavaScript

More info about booleans:

• Booleans in JavaScript

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