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ECMAScript 2021


JavaScript Version Numbers
Old JS versions are named by numbers: ES5 (2009) and ES6 (2015).
From 2016, versions are named by year: ECMAScript 2016, 2017, 2018, 2019, ...

New Features in ES2021

Promise any():const first = await Promise.any([prom1,prom2,prom3]);
String replaceAll()
Numeric Separators (_)


New Features in ES2022

Array at()
String at()
RegExp /d
Object.hasOwn()
error.cause
await import
Private methods and fields
Class field declarations


Warning
These features are relatively new.
Older browsers may need an alternative code (Polyfill)



JavaScript String ReplaceAll()
ES2021 introduced the string method replaceAll():

Example

text = text.replaceAll("Cats","Dogs");
text = text.replaceAll("cats","dogs");

Try it Yourself »

The replaceAll() method allows you to specify a
regular expression instead of a string to be replaced.
If the parameter is a regular expression, the global flag (g) must be set, otherwise
a TypeError is thrown.

Example

text = text.replaceAll(/Cats/g,"Dogs");
text = text.replaceAll(/cats/g,"dogs");

Try it Yourself »


Note
ES2020 introduced the string method matchAll().









JavaScript Numeric Separator (_)
ES2021 intoduced the numeric separator (_) to make numbers more readable:

Example

const num = 1_000_000_000;

Try it Yourself »

The numeric separator is only for visual use.

Example

const num1 = 1_000_000_000;
const num2 = 1000000000;
(num1 === num2);

Try it Yourself »

The numeric separator can be placed anywhere in a number:

Example

const num1 = 1_2_3_4_5;

Try it Yourself »


Note
The numeric separator is not allowed at the beginning or at the end of a number.
In JavaScript only variables can start with _.

The numeric separator is supported in all modern browsers since January 2020:










Chrome 75
Edge 79
Firefox 74
Safari 13.1
Opera 67


Jun 2019
Jan 2020
Oct 2019
Sep 2019
Jun 2019





JavaScript Array at()
ES2022 intoduced the array method at():

Examples
Get the third element of fruits:

const fruits = ["Banana", "Orange", "Apple", "Mango"];
let fruit = fruits.at(2);

Try it Yourself »
Get the third element of fruits:

const fruits = ["Banana", "Orange", "Apple", "Mango"];
let fruit = fruits[2];

Try it Yourself »

The at() method returns an indexed element from an array.
The at() method returns the same as [].
The at() method is supported in all modern browsers since March 2022:










Chrome 92
Edge 92
Firefox 90
Safari 15.4
Opera 78


Apr 2021
Jul 2021
Jul 2021
Mar 2022
Aug 2021




Note
Many languages allows negative bracket indexing like [-1] to access elements from the end of an
object / array / string.
This is not possible in JavaScript, because [] is used for accessing both arrays and objects.
obj[-1] refers to the value of key -1, not to the last property of the object.
The at() method was introduced in ES2022 to solve this problem.



JavaScript String at()
ES2022 intoduced the string method at():

Examples
Get the third letter of name:

const name = "W3Schools";
let letter = name.at(2);

Try it Yourself »
Get the third letter of name:

const name = "W3Schools";
let letter = name[2];

Try it Yourself »

The at() method returns an indexed element from an string.
The at() method returns the same as [].
The at() method is supported in all modern browsers since March 2022:










Chrome 92
Edge 92
Firefox 90
Safari 15.4
Opera 78


Apr 2021
Jul 2021
Jul 2021
Mar 2022
Aug 2021
















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+1

Reference: https://www.w3schools.com/js/js_2021.asp