Array.prototype.includes(value) returns true if the value appears at least once, otherwise false. It is a read-only membership test (ES2016). Prefer it over indexOf() !== -1 when you only need yes/no — and when you care about NaN.
array.includes(value)
array.includes(value, fromIndex)
[1, 2, 3].includes(2) → true
[1, 2, 3].includes(9) → false
[NaN].includes(NaN) → true // indexOf fails here
SameValueZero (≈ ===, but NaN matches NaN)
does not mutate the arrayCall array.includes. Start with this line.
array.includes(value, fromIndex = 0)| Call | What it does |
|---|---|
array.includes(value, fromIndex = 0) | Primary signature. |
array.includes(...) | Call with the arguments your case needs. |
Built into JavaScript. Call includes(...) on an array instance — no import required.
array.includes(value, fromIndex = 0)| Parameter | Description |
|---|---|
| Array | Required. Source to search |
| value | Required. Value to look for |
| fromIndex | Optional. Start index; negative counts from the end |
| Return Value | Description |
|---|---|
| * | true or false |
Ask whether a value exists — get a clear boolean.
const numbers = [1, 2, 3, 4, 5];
console.log(numbers.includes(3)); // true
console.log(numbers.includes(10)); // false1 through 5.true.false.-1.fromIndexSkip earlier elements when you only care about a suffix of the array.
const numbers = [1, 2, 3, 2, 5];
console.log(numbers.includes(2)); // true (index 1)
console.log(numbers.includes(2, 3)); // true (index 3)
console.log(numbers.includes(2, 4)); // false2 near the start.2; still finds the later one.5 remains → false.includes vs indexOf (and NaN)Use includes for membership; use indexOf when you need the index. Prefer includes for NaN.
const values = [1, NaN, 3];
console.log(values.includes(NaN)); // true
console.log(values.indexOf(NaN)); // -1
console.log(values.includes(1)); // true
console.log(values.indexOf(1)); // 0NaN as equal to itself.NaN === NaN is false.1; indexOf also gives position 0.includes; index → indexOf.Array.prototype.includes() is part of ES2016 (ES7). It has been available in evergreen browsers and Node.js for years.
Supported in Chrome 47+, Firefox 43+, Safari 9+, Edge 14+, and Node.js 6+. Not available in Internet Explorer without a polyfill.
Bottom line: Safe for almost all modern web apps and Node LTS releases. For IE11, feature-detect with if ("includes" in Array.prototype) or use a polyfill / indexOf() !== -1 (with care for NaN).
Find the index of a value — or get -1 when it is missing.
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