TypeScript Array lastIndexOf()
Syntax & Examples

Array.lastIndexOf() method

The lastIndexOf() method returns the index of the last occurrence of a specified value in an array, or -1 if it is not present. The array is searched backwards, starting at fromIndex.

Syntax of Array.lastIndexOf()

The syntax of Array.lastIndexOf() method is:

lastIndexOf(searchElement: T, fromIndex?: number): number

This lastIndexOf() method of Array returns the index of the last occurrence of a specified value in an array.

Parameters

ParameterOptional/RequiredDescription
searchElementrequiredThe element to locate in the array.
fromIndexoptionalThe index at which to start searching backwards. Defaults to the array's length minus one (arr.length - 1).

Return Type

Array.lastIndexOf() returns value of type number.


✐ Examples

1 Using lastIndexOf() to find the last occurrence of a number

The lastIndexOf() method can be used to find the index of the last occurrence of a number in an array.

For example,

  1. Create an array arr with numeric values [1, 2, 3, 1, 2, 3].
  2. Use lastIndexOf(2) to find the last occurrence of the number 2 in the array.
  3. Store the result in index.
  4. Log index to the console.

TypeScript Program

const arr = [1, 2, 3, 1, 2, 3];
const index = arr.lastIndexOf(2);
console.log(index);

Output

4

2 Using lastIndexOf() to find the last occurrence of a string

The lastIndexOf() method can be used to find the index of the last occurrence of a string in an array.

For example,

  1. Create an array arr with string values ['apple', 'banana', 'cherry', 'apple'].
  2. Use lastIndexOf('apple') to find the last occurrence of the string 'apple' in the array.
  3. Store the result in index.
  4. Log index to the console.

TypeScript Program

const arr = ['apple', 'banana', 'cherry', 'apple'];
const index = arr.lastIndexOf('apple');
console.log(index);

Output

3

3 Using lastIndexOf() with a fromIndex parameter

The lastIndexOf() method can be used with a fromIndex parameter to start the search from a specific index.

For example,

  1. Create an array arr with numeric values [1, 2, 3, 1, 2, 3].
  2. Use lastIndexOf(2, 3) to find the last occurrence of the number 2 in the array, starting the search from index 3.
  3. Store the result in index.
  4. Log index to the console.

TypeScript Program

const arr = [1, 2, 3, 1, 2, 3];
const index = arr.lastIndexOf(2, 3);
console.log(index);

Output

1

Summary

In this TypeScript tutorial, we learned about lastIndexOf() method of Array: the syntax and few working examples with output and detailed explanation for each example.