Java Script Array indexOf()

In this tutorial, we will learn about the JavaScript Array indexOf() method with the help of examples.

The indexOf() method returns the first index of occurance of an array element, or -1 if it is not found.

Syntax

			
					arr.indexOf(searchValue, fromIndex)

Here arr is an Array

Parameters

searchValue ( required ) - The element to locate in the array.
fromIndex (optional) - The index to start the search at. By default, it is 0.

Return Value

A Number - The first position where the search-value occurs.
Returns -1 if the element is not found in the array.

indexOf() method uses the strict equality comparison algorithm (similar to the triple-equals operator or ===) compares searchValue

Using indexOf() method example

			
					const countries = ["UK", "USA", "Germany", "Spain"];
console.log(countries.indexOf("USA"));
console.log(countries.indexOf("Spain"));

OutPut

1
3

No Occurrence is Found

			
					const countries = ["UK", "USA", "Germany", "Spain"];
// if not found , returns -1
console.log(countries.indexOf("Italy"));

Output

-1

Suppose, you have an array marks that consists of six numbers

			
					const marks = [ 11, 22, 33, 44, 55, 66 ];

The indexOf() method to find the elements in the marks array

			
					console.log(marks.indexOf(11)); // 0
console.log(marks.indexOf(44)); // 3
console.log(marks.indexOf(66)); // 5
console.log(marks.indexOf(33)); // 2
console.log(marks.indexOf(22)); // 1
console.log(marks.indexOf(55)); // 4

Case Sensitive

The indexOf() is case-sensitive. Lets See the example

			
					const countries = ["UK", "USA", "Germany", "Spain"];
// case-senstive
console.log(countries.indexOf("usa")); // -1

To Overcome , You can convert string in an array to lowercase before using the indexOf() method.

			
					const countries = ["UK", "USA", "Germany", "Spain"];
// Convert Each Item to LowerCase
const sameCaseCountries = countries.map((e) => e.toLowerCase());
console.log(sameCaseCountries.indexOf("usa".toLowerCase()));
console.log(sameCaseCountries.indexOf("SpAin".toLowerCase()));