findLastIndex
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.
Similar to findIndex
, findLastIndex
returns the index of the first element that matches the condition, but it starts searching from the right.
You can specify the condition in several ways:
- Predicate function: If you provide a predicate function, the function will be applied to each item. The first item that makes the predicate function return
true
will be selected. - Partial object: If you provide a partial object, the function will return the first item that matches the properties of the partial object.
- Property-value pair: If you provide a property-value pair, the function will return the first item that matches the property and value from the pair.
- Property name: If you provide a property name, the function will return the first item where the specified property has a truthy value.
Signature
typescript
function findLastIndex<T>(
arr: T[],
doesMatch: (item: T, index: number, arr: T[]) => unknown,
fromIndex?: number
): number;
function findLastIndex<T>(arr: T[], doesMatch: Partial<T>, fromIndex?: number): number;
function findLastIndex<T>(arr: T[], doesMatch: [keyof T, unknown], fromIndex?: number): number;
function findLastIndex<T>(arr: T[], doesMatch: string, fromIndex?: number): number;
Parameters
arr
(T[]
): The array to search through.doesMatch
:- Predicate function (
(item: T, index: number, arr: readonly T[]) => unknown
): A function that takes an item, its index, and the array, and returns a truthy value if the item matches the criteria. - Partial object (
Partial<T>
): A partial object that specifies the properties to match. - Property-value pair (
[keyof T, unknown]
): An array where the first element is the property key and the second element is the value to match. - Property name (
string
): The name of the property to check for a truthy value.
- Predicate function (
fromIndex
(number
): The index to start the search from, defaults to the last index of the array (arr.length - 1
).
Returns
(number
): The index of the first item that has the specified property value, or -1
if no match is found.
Examples
typescript
import { findLastIndex } from 'es-toolkit/compat';
// Using a predicate function
const items = [1, 2, 3, 4, 5];
const result = findLastIndex(items, item => item > 3);
console.log(result); // 4
// Using a partial object
const items = [
{ id: 1, name: 'Alice' },
{ id: 2, name: 'Bob' },
];
const result = findLastIndex(items, { name: 'Bob' });
console.log(result); // 1
// Using a property-value pair
const items = [
{ id: 1, name: 'Alice' },
{ id: 2, name: 'Bob' },
];
const result = findLastIndex(items, ['name', 'Alice']);
console.log(result); // 0
// Using a property name
const items = [
{ id: 1, name: 'Alice' },
{ id: 2, name: 'Bob' },
];
const result = findLastIndex(items, 'name');
console.log(result); // 1