Array.prototype.indexOf()

indexOf(searchElement, fromIndex)

Returns: number · Updated March 13, 2026 · Array Methods

array indexof search find

indexOf() searches an array from left to right and returns the first index where the given element is found. Returns -1 when the element is not found.

Syntax

indexOf(searchElement)
indexOf(searchElement, fromIndex)

Parameters

Parameter	Type	Default	Description
`searchElement`	any	—	The value to search for in the array
`fromIndex`	number	`0`	The index to start searching from

Examples

Basic usage

const fruits = ["apple", "banana", "orange", "banana", "melon"];

console.log(fruits.indexOf("banana"));
// 1

console.log(fruits.indexOf("grape"));
// -1

Using fromIndex

const letters = ["a", "b", "c", "b", "a"];

// Start searching from index 2
console.log(letters.indexOf("b", 2));
// 3

Finding all occurrences

const numbers = [1, 2, 3, 2, 1, 2, 3];
const target = 2;
const indices = [Global_Objects::eval];

let index = numbers.indexOf(target);
while (index !== -1) {
  indices.push(index);
  index = numbers.indexOf(target, index + 1);
}

console.log(indices);
// [1, 3, 5]

Common Patterns

Checking if an element exists

const users = ["alice", "bob", "charlie"];

if (users.indexOf("bob") !== -1) {
  console.log("User found");
}
// User found

// Or simply
const exists = users.includes("bob");
console.log(exists);
// true

Removing specific occurrences

const items = ["a", "b", "c", "b", "d"];
const toRemove = "b";

const idx = items.indexOf(toRemove);
if (idx !== -1) {
  items.splice(idx, 1);
}

console.log(items);
// ['a', 'c', 'b', 'd']

Strict Equality

indexOf uses strict equality (===) for comparison. Objects are compared by reference, not by value.

const objects = [{ id: 1 }, { id: 2 }];
const found = objects.indexOf({ id: 1 });

console.log(found);
// -1 — different object reference

// To find by property, use findIndex()
const foundByProp = objects.findIndex(obj => obj.id === 1);
console.log(foundByProp);
// 0