ECMAScript 2024
New Features in JavaScript 2024
| Feature | Description | |
|---|---|---|
| Object groupBy() |
Groups object elements according to values returned from a callback function | |
| Map groupBy() |
Groups map elements according to values returned from a callback function | |
| String isWellFormed() |
Returns true if a string is well formed | |
| String toWellFormed() |
Returns a new string where "lone surrogates" are replaced with Unicode U+FFFD | |
| Promise withResolvers() | ||
| Atomics waitAsync |
Warning
These features are relatively new.
Older browsers may need an alternative code (Polyfill)
JavaScript Object.groupBy()
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 »
Description
The Object.groupBy() method groups elements of an object
according to string values returned from a callback function.
The Object.groupBy() method return a new object.
The Object.groupBy() method does not change the original object.
Note:
The elements in the original and in the returned object are the same.
Future changes will be reflected in both the original and in the returned object.
JavaScript Map.groupBy()
Example
// Create a Map
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 = Map.groupBy(fruits, myCallback);
Try it Yourself »
Description
The Map.groupBy() method groups elements of a map
according to string values returned from a callback function.
The Map.groupBy() method returns a new map.
The Map.groupBy() method does not change the original object.
Note:
The elements in the original and in the returned object are the same.
Future changes will be reflected in both the original and in the returned object.
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 String isWellFormed()
The isWellFormed() method returns true
if a string is well formed.
Otherwise it returns false.
A string is not well formed if it contains lone surrogates.
Examples
let text = "Hello world!";
let result = text.isWellFormed();
Try it Yourself »
let text = "Hello World \uD800";
let result = text.isWellFormed();
Try it Yourself »
Lone Surrogates
A lone surrogate is a Unicode surrogate code point that is not part of a valid surrogate pair used to represent characters in UTF-16 encoding.
JavaScript String toWellFormed()
The String method toWellFormed()
returns a new string where all "lone surrogates" are replaced with the Unicode replacement character (U+FFFD).
