TypeScript Array indexOf() Method

The Array.indexOf() method in TypeScript is used to find the index of the first occurrence of a specified element in an array. If the element is not found, it returns -1.

Syntax

array.indexOf(searchElement[, fromIndex])

Parameter: This method accepts two parameters as mentioned above and described below: 

• searchElement: This parameter is the Element to locate in the array.
• fromIndex: This parameter is the index at which to begin the search.

Return Value: This method returns the index of the found element. 

The below examples illustrate the Array indexOf() method in TypeScript.

Example 1: Finding an Element in an Array

In this example, the indexOf() method is used to find the index of the first occurrence of the element 5 in the array.

let numbers: number[] = [1, 2, 3, 5, 5, 6];
let index = numbers.indexOf(5);
console.log(index); // Output: 3

Output: 

3

Example 2: Searching from a Specific Index

In this example, the indexOf() method is used to find the index of the element 5 in the array, starting the search from index 4.

let numbers: number[] = [1, 2, 3, 5, 5, 6];
let index = numbers.indexOf(5, 4);
console.log(index); // Output: 4

Output: 

4

Example 3: Element Not Found

In this example, the indexOf() method is used to search for an element 10 that is not present in the array.

let numbers: number[] = [1, 2, 3, 5, 6];
let index = numbers.indexOf(10);
console.log(index); // Output: -1

Output:

-1