ECMAScript 2021

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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");

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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");

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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;

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The numeric separator is only for visual use.

Example

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

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The numeric separator can be placed anywhere in a number:

Example

const num1 = 1_2_3_4_5;

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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);

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Get the third element of fruits:

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

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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 = "91xjr";
let letter = name.at(2);

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Get the third letter of name:

const name = "91xjr";
let letter = name[2];

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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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