Menu
×
   ❮     
HTML CSS JAVASCRIPT SQL PYTHON JAVA PHP HOW TO W3.CSS C C++ C# BOOTSTRAP REACT MYSQL JQUERY EXCEL XML DJANGO NUMPY PANDAS NODEJS R TYPESCRIPT ANGULAR GIT POSTGRESQL MONGODB ASP AI GO KOTLIN SASS VUE DSA GEN AI SCIPY AWS CYBERSECURITY DATA SCIENCE
     ❯   

JS Tutorial

JS HOME JS Introduction JS Where To JS Output JS Statements JS Syntax JS Comments JS Variables JS Let JS Const JS Operators JS Arithmetic JS Assignment JS Data Types JS Functions JS Objects JS Object Properties JS Object Methods JS Object Display JS Object Constructors JS Events JS Strings JS String Methods JS String Search JS String Templates JS Numbers JS BigInt JS Number Methods JS Number Properties JS Arrays JS Array Methods JS Array Search JS Array Sort JS Array Iteration JS Array Const JS Dates JS Date Formats JS Date Get Methods JS Date Set Methods JS Math JS Random JS Booleans JS Comparisons JS If Else JS Switch JS Loop For JS Loop For In JS Loop For Of JS Loop While JS Break JS Iterables JS Sets JS Set Methods JS Maps JS Map Methods JS Typeof JS Type Conversion JS Destructuring JS Bitwise JS RegExp JS Precedence JS Errors JS Scope JS Hoisting JS Strict Mode JS this Keyword JS Arrow Function JS Classes JS Modules JS JSON JS Debugging JS Style Guide JS Best Practices JS Mistakes JS Performance JS Reserved Words

JS Versions

JS Versions JS 2009 (ES5) JS 2015 (ES6) JS 2016 JS 2017 JS 2018 JS 2019 JS 2020 JS 2021 JS 2022 JS 2023 JS 2024 JS IE / Edge JS History

JS Objects

Object Definitions Object Prototypes Object Methods Object Properties Object Get / Set Object Protection

JS Functions

Function Definitions Function Parameters Function Invocation Function Call Function Apply Function Bind Function Closures

JS Classes

Class Intro Class Inheritance Class Static

JS Async

JS Callbacks JS Asynchronous JS Promises JS Async/Await

JS HTML DOM

DOM Intro DOM Methods DOM Document DOM Elements DOM HTML DOM Forms DOM CSS DOM Animations DOM Events DOM Event Listener DOM Navigation DOM Nodes DOM Collections DOM Node Lists

JS Browser BOM

JS Window JS Screen JS Location JS History JS Navigator JS Popup Alert JS Timing JS Cookies

JS Web APIs

Web API Intro Web Forms API Web History API Web Storage API Web Worker API Web Fetch API Web Geolocation API

JS AJAX

AJAX Intro AJAX XMLHttp AJAX Request AJAX Response AJAX XML File AJAX PHP AJAX ASP AJAX Database AJAX Applications AJAX Examples

JS JSON

JSON Intro JSON Syntax JSON vs XML JSON Data Types JSON Parse JSON Stringify JSON Objects JSON Arrays JSON Server JSON PHP JSON HTML JSON JSONP

JS vs jQuery

jQuery Selectors jQuery HTML jQuery CSS jQuery DOM

JS Graphics

JS Graphics JS Canvas JS Plotly JS Chart.js JS Google Chart JS D3.js

JS Examples

JS Examples JS HTML DOM JS HTML Input JS HTML Objects JS HTML Events JS Browser JS Editor JS Exercises JS Quiz JS Website JS Interview Prep JS Bootcamp JS Certificate

JS References

JavaScript Objects HTML DOM Objects


ECMAScript 2017

JavaScript Version Numbers

Old ECMAScript versions was named by numbers: ES5 and ES6.

From 2016, versions are named by year: ES2016, 2018, 2020 ...

New Features in ECMAScript 2017

This chapter introduces the new features in ECMAScript 2017:

ES 2017 is fully supported in all modern browsers since September 2017:

Chrome 57 Edge 15 Firefox 48 Safari 11 Opera 44
Mar 2017 Apr 2017 Aug 2016 Sep 2017 Mar 2017

JavaScript String Padding

ECMAScript 2017 added two string methods to JavaScript: padStart() and padEnd() to support padding at the beginning and at the end of a string.

Examples

let text = "5";
text = text.padStart(4,0);
Try it Yourself »
let text = "5";
text = text.padEnd(4,0);
Try it Yourself »

JavaScript string padding is supported in all modern browsers since April 2017:

Chrome 57 Edge 15 Firefox 48 Safari 10 Opera 44
Mar 2017 Apr 2017 Aug 2016 Sep 2016 Mar 2017

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:

Chrome 47 Edge 14 Firefox 47 Safari 10.1 Opera 41
Jun 2016 Aug 2016 Jun 2016 Mar 2017 Oct 2016

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:

Chrome 54 Edge 14 Firefox 47 Safari 10.1 Opera 41
Oct 2016 Aug 2016 Jun 2016 Mar 2017 Oct 2016


JavaScript Async Functions

Waiting for a Timeout

async function myDisplay() {
  let myPromise = new Promise(function(myResolve, myReject) {
    setTimeout(function() { myResolve("I love You !!"); }, 3000);
  });
  document.getElementById("demo").innerHTML = await myPromise;
}

myDisplay();

Try it Yourself »

Async functions are supported in all modern browsers since September 2017:

Chrome 55 Edge 15 Firefox 52 Safari 11 Opera 42
Dec 2016 Apr 2017 Mar 2017 Sep 2017 Dec 2016

JavaScript Trailing Commas

JavaScript allows trailing commas wherever a comma-separated list of values is accepted.

In Array and Object Literals, Function Calls, Parameters, Imports and Exports.

Example

function myFunc(x,,,) {};
const myArr = [1,2,3,4,,,];
const myObj = {fname: John, age:50,,,};

Trailing commas are supported in all modern browsers since May 2017:

Chrome 58 Edge 14 Firefox 52 Safari 10 Opera 45
Apr 2017 Aug 2016 Mar 2017 Sep 2016 May 2017


×

Contact Sales

If you want to use W3Schools services as an educational institution, team or enterprise, send us an e-mail:
sales@w3schools.com

Report Error

If you want to report an error, or if you want to make a suggestion, send us an e-mail:
help@w3schools.com

W3Schools is optimized for learning and training. Examples might be simplified to improve reading and learning. Tutorials, references, and examples are constantly reviewed to avoid errors, but we cannot warrant full correctness of all content. While using W3Schools, you agree to have read and accepted our terms of use, cookie and privacy policy.

Copyright 1999-2024 by Refsnes Data. All Rights Reserved. W3Schools is Powered by W3.CSS.