JavaScript Array indexOf()

Find the first index of "Apple":

const fruits = ["Banana", "Orange", "Apple", "Mango"];
let index = fruits.indexOf("Apple");

Start at index 3:

const fruits = ["Banana", "Orange", "Apple", "Mango", "Apple"];
let index = fruits.indexOf("Apple", 3);

More examples below.

Description

The indexOf() method returns the first index (position) of a specified value.

The indexOf() method returns -1 if the value is not found.

The indexOf() method starts at a specified index and searches from left to right.

By default the search starts at the first element and ends at the last.

Negative start values counts from the last element (but still searches from left to right).

Method	Finds
indexOf()	The value of the first element with a specified value
lastIndexOf()	The index of the last element with a specified value
find()	The value of the first element that passes a test
findIndex()	The index of the first element that passes a test
findLast()	The value of the last element that passes a test
findLastIndex()	The index of the last element that passes a test

array.indexOf(item, start)

Parameter	Description
item	Required. The value to search for.
start	Optional. Where to start the search. Default value is 0. Negative values start the search from the end of the array.