JavaScript Array.findIndex() Method

Array.findIndex()

The Array.findIndex() method in JavaScript is used to find the index of the first element in an array that satisfies a provided testing function. If no elements satisfy the testing function, it returns -1.

Syntax

findIndex(callbackFn)
findIndex(callbackFn, thisArg)

Parameters

Parameter	Description
callbackFn	A function to execute on each element in the array. It should return a truthy value for the element to be considered a match.
thisArg (optional)	A value to use as this when executing callbackFn.

Return Value

The findIndex() method returns the index of the first element in the array that satisfies the callbackFn. If no such element is found, it returns -1.

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Examples

1. Finding the Index of an Element

This example demonstrates how to use findIndex() to locate the index of the first even number in an array.

const numbers = [1, 3, 7, 8, 10];

const index = numbers.findIndex((num) => num % 2 === 0);
console.log(index);

Output

3

The first even number is 8, located at index 3.

2. Using thisArg with findIndex()

This example demonstrates the use of the optional thisArg parameter to define the this context for the callback function.

const threshold = { limit: 5 };

const numbers = [1, 6, 8, 3, 4];

const index = numbers.findIndex(function (num) {
    return num > this.limit;
}, threshold);

console.log(index);

Output

1

The first element greater than 5 is 6, located at index 1. The thisArg sets this.limit to 5.

3. No Matching Element

When no element satisfies the condition, findIndex() returns -1.

const numbers = [1, 3, 5, 7];

const index = numbers.findIndex((num) => num % 2 === 0);
console.log(index);

Output

-1

There are no even numbers in the array, so the method returns -1.

4. Using findIndex() with Objects

The findIndex() method can also be used to find the index of an object in an array based on a condition.

const users = [
    { id: 1, name: "Akash" },
    { id: 2, name: "Bhairav" },
    { id: 3, name: "Charlie" }
];

const index = users.findIndex((user) => user.name === "Bhairav");
console.log(index);

Output

1

The object representing Bhairav is located at index 1.