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JS Tutorial

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JS References

JavaScript Objects HTML DOM Objects


JavaScript Object Methods


General Methods

// Copies properties from a source object to a target object
Object.assign(target, source)

// Creates an object from an existing object
Object.create(object)

// Returns an array of the key/value pairs of an object
Object.entries(object)

// Creates an object from a list of keys/values
Object.fromEntries()

// Returns an array of the keys of an object
Object.keys(object)

// Returns an array of the property values of an object
Object.values(object)

// Groups object elements according to a function
Object.groupBy(object, callback)

JavaScript Object.assign()

The Object.assign() method copies properties from one or more source objects to a target object.

Example

// Create Target Object
const person1 = {
  firstName: "John",
  lastName: "Doe",
  age: 50,
  eyeColor: "blue"
};

// Create Source Object
const person2 = {firstName: "Anne",lastName: "Smith"};

// Assign Source to Target
Object.assign(person1, person2);
Try it Yourself »

JavaScript Object.entries()

ECMAScript 2017 added the Object.entries() method to objects.

Object.entries() returns an array of the key/value pairs in an object:

Example

const person = {
  firstName : "John",
  lastName : "Doe",
  age : 50,
  eyeColor : "blue"
};

let text = Object.entries(person);
Try it Yourself »

Object.entries() makes it simple to use objects in loops:

Example

const fruits = {Bananas:300, Oranges:200, Apples:500};

let text = "";
for (let [fruit, value] of Object.entries(fruits)) {
  text += fruit + ": " + value + "<br>";
}
Try it Yourself »

Object.entries() also makes it simple to convert objects to maps:

Example

const fruits = {Bananas:300, Oranges:200, Apples:500};

const myMap = new Map(Object.entries(fruits));
Try it Yourself »

Object.entries() is supported in all modern browsers since March 2017:


JavaScript Object.fromEntries()

The fromEntries() method creates an object from a list of key/value pairs.

Example

const fruits = [
  ["apples", 300],
  ["pears", 900],
  ["bananas", 500]
];

const myObj = Object.fromEntries(fruits);
Try it Yourself »


JavaScript Object.values()

Object.values() is similar to Object.entries(), but returns a single dimension array of the object values:

Example

const person = {
  firstName : "John",
  lastName : "Doe",
  age : 50,
  eyeColor : "blue"
};

let text = Object.values(person);
Try it Yourself »

Object.values() is supported in all modern browsers since March 2017:


JavaScript Object.groupBy()

ES2024 added the Object.groupBy() method to JavaScript.

The Object.groupBy() method groups elements of an object according to string values returned from a callback function.

The Object.groupBy() method does not change the original object.

Example

// Create an Array
const fruits = [
  {name:"apples", quantity:300},
  {name:"bananas", quantity:500},
  {name:"oranges", quantity:200},
  {name:"kiwi", quantity:150}
];

// Callback function to Group Elements
function myCallback({ quantity }) {
  return quantity > 200 ? "ok" : "low";
}

// Group by Quantity
const result = Object.groupBy(fruits, myCallback);
Try it Yourself »

Browser Support

Object.groupby() is an ES2024 feature.

It is supported in new browsers since March 2024:

Chrome 117 Edge 117 Firefox 119 Safari 17.4 Opera 103
Sep 2023 Sep 2023 Oct 2023 Okt 2024 May 2023

Warning

ES2024 features are relatively new.

Older browsers may need an alternative code (Polyfill)


Object.groupBy() vs Map.groupBy()

The difference between Object.groupBy() and Map.groupBy() is:

Object.groupBy() groups elements into a JavaScript object.

Map.groupBy() groups elements into a Map object.


JavaScript Object.keys()

The Object.keys() method returns an array with the keys of an object.

Example

// Create an Object
const person = {
  firstName: "John",
  lastName: "Doe",
  age: 50,
  eyeColor: "blue"
};

// Get the Keys
const keys = Object.keys(person);
Try it Yourself »

JavaScript for...in Loop

The JavaScript for...in statement loops through the properties of an object.

Syntax

for (let variable in object) {
  // code to be executed
}

The block of code inside of the for...in loop will be executed once for each property.

Looping through the properties of an object:

Example

const person = {
  fname:" John",
  lname:" Doe",
  age: 25
};

for (let x in person) {
  txt += person[x];
}
Try it Yourself »

Complete Object Reference

For a complete reference, go to our:

Complete JavaScript Object Reference.

The reference contains descriptions and examples of all Object Properties and Methods.


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