Array

`Object.groupBy`

Groups the elements of an iterable according to the string values returned by a provided callback function

Syntax

JavaScript

Object.groupBy(iterable, callbackFn)

Parameters

Parameter	Type	Description
iterable	Iterable<T>	An iterable whose elements will be grouped
callbackFn	(element, index) => string	Function that returns the group key for each element

Return Value

A null-prototype object with properties for each group containing arrays of group members

Examples

Basic Usage

const inventory = [
  { name: 'asparagus', type: 'vegetables' },
  { name: 'bananas', type: 'fruit' },
  { name: 'goat', type: 'meat' },
  { name: 'cherries', type: 'fruit' },
];
const result = Object.groupBy(inventory, ({ type }) => type);
console.log(result.fruit?.length); // 2

Practical Example

const numbers = [1, 2, 3, 4, 5, 6];
const grouped = Object.groupBy(numbers, n =>
  n % 2 === 0 ? 'even' : 'odd'
);
console.log(grouped.even); // [2, 4, 6]

Advanced Usage

const words = ['hello', 'hi', 'world', 'web'];
const byLetter = Object.groupBy(words, w => w[0]);
console.log(byLetter.h); // ['hello', 'hi']

Understanding Object.groupBy

The Object.groupBy method in JavaScript groups the elements of an iterable according to the string values returned by a provided callback function. It belongs to the Array object and is one of the most widely used methods for working with array values in modern JavaScript and TypeScript applications.

The method signature is Object.groupBy(iterable, callbackFn). It accepts 2 parameters: iterable, callbackFn. When called, it returns a null-prototype object with properties for each group containing arrays of group members. Understanding when and how to use groupBy() helps you write more expressive, readable code.

Common use cases for Object.groupBy include data transformation, input validation, API response processing, and building reusable utility functions. It works well alongside related methods like array-reduce, array-filter, array-map, enabling you to chain operations together for complex data manipulation pipelines.

Supported in Chrome 117+, Firefox 119+, Safari 17.4+, Edge 117+, and Node.js 21+.

Browser Compatibility

Supported in Chrome 117+, Firefox 119+, Safari 17.4+, Edge 117+, and Node.js 21+.

Related Methods

Array.prototype.reduce

Executes a user-supplied reducer callback function on each element of the array, passing in the return value from the calculation on the preceding element

Array.prototype.filter

Creates a shallow copy of a portion of a given array, filtered down to just the elements that pass the test implemented by the provided function

Array.prototype.map

Creates a new array populated with the results of calling a provided function on every element in the calling array

Object.fromEntries

Transforms a list of key-value pairs into an object