JS 2025

New Features in JavaScript 2025

The 16th edition of the ECMAScript standard, released in June 2025, includes several enhancements to make JavaScript more readable and efficient.

New Set Features in ES2025

JavaScript 2025 includes built-in methods for set operations, such as intersection(), union(), and difference(), eliminating the need for manual loops or third-party libraries.

New Iterator Helpers in ES2025

The introduction of an Iterator object provides a functional interface with lazy evaluation, allowing developers to wrap various iterators like Arrays.

A new set of functional operators for iterators (like .map(), .filter(), and .take()) allows for lazy evaluation, improving performance when handling large data streams.

Other New Features in ES2025

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

JavaScript Set union()

The union() method returns the union of two sets.

The union() method returns a new set containing the elements which are in this set, or in the argument set, or in both:

Example

const A = new Set(['a','b','c']);

const B = new Set(['b','c','d']);

const C = A.union(B);

The union() method is supported in all modern browsers since June 2024:

JavaScript Set intersection()

The intersection() method returns the intersection of two sets.

The intersection() method returns a new set containing the elements which are in this set and in the argument set:

Example

const A = new Set(['a','b','c']);

const B = new Set(['b','c','d']);

const C = A.intersection(B);

The intersection() method is supported in all modern browsers since June 2024:

JavaScript Set difference()

The difference() method returns the difference between two sets.

The difference() method returns a new set containing elements which are in this set but not in the argument set:

Example

const A = new Set(['a','b','c']);

const B = new Set(['b','c','d']);

const C = A.difference(B);

The difference() method is supported in all modern browsers since June 2024:

JavaScript Set symmetricDifference()

The symmetricDifference() method returns the symmetric difference between to sets.

The symmetricDifference() method returns a new set containing elements which are in this set or in the argument set, but not in both:

Example

const A = new Set(['a','b','c']);

const B = new Set(['b','c','d']);

const C = A.symmetricDifference(B);

The symmetricDifference() method is supported in all modern browsers since June 2024:

JavaScript Set isSubsetOf()

The isSubsetOf() method returns true if all elements in this set are elements in the argument set:

Example

const A = new Set(['a','b','c']);

const B = new Set(['b','c','d']);

let answer = A.isSubsetOf(B);

The isSubsetOf() method is supported in all modern browsers since June 2024:

JavaScript Set isSupersetOf()

The isSupersetOf() method returns true if all elements in the argument set are also in this set:

Example

const A = new Set(['a','b','c']);

const B = new Set(['b','c','d']);

let answer = A.isSupersetOf(B);

The isSupersetOf() method is supported in all modern browsers since June 2024:

JavaScript Set isDisjointFrom()

The isDisjointFrom() method returns true if this set has no elements in common with the argument set:

Example

const A = new Set(['a','b','c']);

const B = new Set(['b','c','d']);

let answer = A.isDisjointFrom(B);

The Set.isDisjointFrom() method is supported in all modern browsers since June 2024:

The Iterator.from() Method

The Iterator.from() creates an iterator object from an existing iterable or iterator object.

Example

// Create an iterator

const myIterator = Iterator.from([1, 2, 3]);

// Iterate over the elements

let text = "";

for (const x of myIterator) {

  text += x;

}

The drop() Method

The drop() method returns a new iterator that skips a specified number of elements before yielding the rest.

Example

// Create an iterator

const myIterator = Iterator.from([1, 2, 3, 4, 5, 6]);

// Remove the first five

const firstFive = myIterator.drop(5);

The every() Method

The every(fn) method returns true if all elements in the iterator satisfy the provided test function.

Example

// Create an Iterator

const myIterator = Iterator.from("123456789");

// Is every Element greater than 7?

let result = myIterator.every(x => x > 7);

The filter() Method

The filter() method returns a new iterator containing elements that satisfy a filter function.

Example

// Create an iterator

const myIterator = Iterator.from([32, 33, 16, 40]);

// Filter the iterator

const filteredIterator = myIterator.filter(x => x > 18);

The find() Method

The find(fn) method returns the first element that satisfies a test function.

Example

// Create an iterator

const myIterator = Iterator.from([3, 10, 18, 30, 20]);

// Find first greater than 18

let result = myIterator.find(x => x > 18);

The flatMap() Method

The flatMap() method returns a new iterator by mapping each element and then flattening the results into a single iterator.

Example

// Create an iterator

const myIterator = Iterator.from([1, 2, 3, 4, 5, 6]);

// Map the Iterator

const mappedIterator = myIterator.flatMap(x => [x, x * 10]);

The forEach() Method

The forEach() method executes a provided function once for each element in the iterator.

Example

// Create an iterator

const myIterator = Iterator.from("123456789");

// Iterate over all elements

let text = "";

myIterator.forEach (x => text += x);

The map() Method

The map() method returns a new iterator with all elements transformed by a map function.

Example

// Create an iterator

const myIterator = Iterator.from("123456789");

// Now you can use the map method

const mappedIterator = myIterator.map(x => x * 2);

The reduce() Method

The reduce() method applies a reducer function against an accumulator and each element to reduce it to a single value.

Example

// Create an Iterator

const myIterator = Iterator.from([175, 50, 25]);

// Reduce the Iterator

let result = myIterator.reduce(myFunc);

The some() Method

The some() method returns true if at least one element in the iterator satisfies the provided test function.

Example

// Create an Iterator

const myIterator = Iterator.from("123456789");

// Is some Element greater than 7?

let result = myIterator.some(x => x > 7);

The take() Method

The take() method returns a new iterator that yields at most a specified number of elements.

Example

const myIterator = Iterator.from([1, 2, 3, 4, 5, 6]);

// Take the first five elements

const firstFive = myIterator.take(5);

The RegExp /v Flag

The v flag is an "upgrade" to the u flag.

The u (unicode) flag enables full Unicode support in regular expressions.

The v flag enables more Unicode-related features.

The new features are:

• The \p escape sequence matches strings, instead of just characters.
• The character class is upgraded to allow intersection, union, and subtraction syntaxes, as well as matching multiple Unicode characters.

Examples

let text = "Hello 😄";

let pattern = /\p{RGI_Emoji}/v;

let result = pattern.test(text);

Note: Using both flags (u and v) results in a SyntaxError.

/regexp/v is supported all in modern browsers since May 2025:

The RegExp.escape() Method

The RegExp.escape() method returns a string where characters that belongs to the regular expression syntax are escaped.

This makes it possible to treat characters like +, *, ?, ^, $, (, ), [, ], {, }, |, and \ literally, and not as part of a regular expression.

Example

// Escape a text for to use as a regular expression

const safe = RegExp.escape("[*]");

// Build a new reglar expression

const regex = new RegExp(safe);

// Text to replace within

const oldText = "[*] is a web school.";

// Perform the replace

const newText = oldText.match(regex, "W3Schools");

RegExp.escape() is supported all in modern browsers since May 2025:

The Float16Array Method

A Float16Array is a TypedArray that stores 16-bit (half-precision) floating-point numbers in the IEEE 754 half-precision format.

Float16Array requires half the memory of Float32Array and a quarter of Float64Array.

Example

const myArr = new Float16Array([1.5, 2.5, 3.5, 4.5]);

let bytes = myArr.BYTES_PER_ELEMENT;

let length = myArr.length;

The Float16Array object is supported in all modern browsers since June 2024:

The Math.f16round Method

The static Math.f16round() method returns the nearest 16-bit floating point representation of a number.

Example

let a = Math.f16round(2.60);

let b = Math.f16round(2.50);

let c = Math.f16round(2.49);

let d = Math.f16round(-2.60);

let e = Math.f16round(-2.50);

let f = Math.f16round(-2.49);

The Math.f16round() method is supported in all modern browsers since June 2024:

The Promise.try() Method

The Promise.try() method starts a promise chain from potentially throwing, synchronous code.

This ensures exceptions are correctly handled as promise rejections.

Example

function compute() {

  return Promise.try(() => {

    const v = mayThrowSync();

    return asyncFunc(v);

  });

}

Modules with Import Attributes

Syntax

import {names} from "module-name" with {key:"data"};

Examples

import config from "config.json" with {type:"json"};

import styles from "styles.css" with {type:"css"};

import data from "data.json" with {type:"json"};