findIndex (Lodash Compatibility)

Use Array.prototype.findIndex

This findIndex function operates slowly due to additional features such as handling various condition formats and fromIndex processing.

Use the faster and more modern Array.prototype.findIndex instead.

Finds the index of the first element in an array that matches a condition.

const index = findIndex(arr, doesMatch, fromIndex);

Reference

findIndex(arr, doesMatch, fromIndex)

Use findIndex when you want to find the position of the first element in an array that matches a specific condition. You can specify the condition in various ways. If no element matches the condition, it returns -1.

When you specify a condition as a function, it executes the function for each element and returns the index of the first element that returns true.

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

const users = [
  { id: 1, name: 'Alice', active: false },
  { id: 2, name: 'Bob', active: true },
  { id: 3, name: 'Charlie', active: true },
];

// Specify condition with a function
findIndex(users, user => user.active);
// Returns: 1

When you specify a condition as a partial object, it returns the index of the first element that matches those properties.

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

// Specify condition with a partial object
findIndex(users, { name: 'Bob', active: true });
// Returns: 1

When you specify a condition as an array of property name and value, it returns the index of the first element whose property matches that value.

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

// Specify condition with a [property, value] array
findIndex(users, ['active', true]);
// Returns: 1

When you specify only a property name, it returns the index of the first element where that property evaluates to true.

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

// Specify condition with a property name
findIndex(users, 'active');
// Returns: 1

When you specify fromIndex, the search starts from that index. Negative values are calculated from the end of the array.

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

// Start search from index 2
findIndex(users, user => user.active, 2);
// Returns: 2

// Search from the second element from the end
findIndex(users, user => user.active, -2);
// Returns: 1

null or undefined are treated as empty arrays.

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

findIndex(null, user => user.active); // -1
findIndex(undefined, 'active'); // -1

Parameters

• arr (ArrayLike<T> | null | undefined): The array to search.
• doesMatch (((item: T, index: number, arr: any) => unknown) | Partial<T> | [keyof T, unknown] | PropertyKey, optional): The matching condition. Can be a function, partial object, key-value pair, or property name.
• fromIndex (number, optional): The index to start the search from. Default is 0.

Returns

(number): Returns the index of the first element that matches the condition. Returns -1 if no element matches.