indexOf()

indexOf<T>(array, value, fromIndex?): number

Gets the index at which the first occurrence of value is found in array.

DEPRECATED

Use array.indexOf(value) directly instead.

Reason:
Native equivalent method now available

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Type Parameters

T: T

The type of elements in the array.

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Parameters

array: T[]

The array to search.

value: T

The value to search for.

fromIndex?: number

The index to search from.

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Returns: number

The index of the matched value, or -1 if not found.

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See Also

• Array.indexOf() - MDN
• Browser support - Can I Use

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Since

2.0.0

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Also known as

findFirstIndex (Effect) · indexOf (Lodash, es-toolkit, Ramda) · ❌ (Remeda, Radashi, Modern Dash, Antfu)

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Example

const numbers = [1, 2, 3, 2, 4];

// ❌ Deprecated approach
const index = indexOf(numbers, 2);
console.log(index); // 1

// ✅ Recommended approach
const indexNative = numbers.indexOf(2);
console.log(indexNative); // 1

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How it works?

Returns the index of the first occurrence of a value. Deprecated: Use array.indexOf() directly.

Native Equivalent

// ❌ indexOf(arr, value)
// ✅ arr.indexOf(value)

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Use Cases

Find element position 📌

Get the index of a specific element.

#find#position#index#search

const colors = ["red", "green", "blue"];
colors.indexOf("green");
// => 1

Check element existence

Determine if an element exists in an array.

#check#exists#presence#validation

const allowed = ["admin", "moderator", "user"];
allowed.indexOf(role) !== -1;
// => true if role is in allowed

Find starting position

Search for an element starting from a specific index.

#find#start#position#search

const items = ["a", "b", "a", "c", "a"];
items.indexOf("a", 2);
// => 2 (first "a" at or after index 2)