indexOf

INFO

This function is only available in es-toolkit/compat for compatibility reasons. It either has alternative native JavaScript APIs or isn’t fully optimized yet.

When imported from es-toolkit/compat, it behaves exactly like lodash and provides the same functionalities, as detailed here.

Finds the index of the first occurrence of a value in an array.

This method is similar to Array.prototype.indexOf, but it also finds NaN values. It uses strict equality (===) to compare elements other than NaN.

Signature

function indexOf<T>(array: T[], searchElement: T, fromIndex?: number): number;

Parameters

• array (T[]): The array to search.

array can be ArrayLike<T> or null or undefined

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

• If array is ArrayLike<T>, it converts it to an array using Array.from(...).
• If array is null or undefined, it is treated as an empty array.

• searchElement (T): The value to search for.
• fromIndex (number, optional): The index to start the search at.

Returns

(number): The index (zero-based) of the first occurrence of the value in the array, or -1 if the value is not found.

Example

const array = [1, 2, 3, NaN];
indexOf(array, 3); // => 2
indexOf(array, NaN); // => 3