indexOf (Lodash Compatibility)

Use Array.prototype.indexOf or Array.prototype.findIndex

This indexOf function operates slowly due to additional logic for handling NaN.

If you're not looking for NaN, use the faster Array.prototype.indexOf. To find NaN, use Array.prototype.findIndex with Number.isNaN.

Finds the index of the first occurrence of a given element in an array.

const index = indexOf(array, searchElement, fromIndex);

Reference

indexOf(array, searchElement, fromIndex?)

Works almost the same as Array.prototype.indexOf, but can find NaN values. Use this when you need to find the position of a specific value in an array.

import { indexOf } from 'es-toolkit/compat';

// Find element in number array
const array = [1, 2, 3, 4];
indexOf(array, 3); // => 2

// Find NaN value (Array.prototype.indexOf cannot find it)
const arrayWithNaN = [1, 2, NaN, 4];
indexOf(arrayWithNaN, NaN); // => 2

You can start searching from a specific index.

import { indexOf } from 'es-toolkit/compat';

const array = [1, 2, 3, 1, 2, 3];
indexOf(array, 2, 2); // => 4 (start searching from index 2)

null or undefined are treated as empty arrays.

import { indexOf } from 'es-toolkit/compat';

indexOf(null, 1); // => -1
indexOf(undefined, 1); // => -1

Parameters

• array (T[]): The array to search.

array can be ArrayLike<T>, null, or undefined

To ensure full compatibility with lodash, the indexOf function handles array as follows:

• If array is ArrayLike<T>, it uses Array.from(...) to convert it to an array.
• If array is null or undefined, it's treated as an empty array.

• searchElement (T): The value to find.
• fromIndex (number, optional): The index to start searching from. If negative, it's calculated from the end of the array. Defaults to 0.

Returns

(number): Returns the index of the first element in the array that matches the given value. Returns -1 if no matching element is found.