JavaScript Array includes() Method

What You’ll Learn

The includes() method checks whether an array contains a value and returns true or false. It uses strict equality (with special NaN handling), supports an optional fromIndex, and is clearer than indexOf() !== -1. This tutorial covers syntax, five examples, and comparisons with related methods.

Introduction

Before includes(), developers often wrote arr.indexOf(value) !== -1 to test membership. The includes() method makes that intent obvious and returns a clean boolean.

Use it in conditionals, guards, and validation—anywhere you need a yes/no answer about whether a value appears in an array.

Understanding the includes() Method

array.includes(searchElement, fromIndex?) scans the array and returns true as soon as a match is found. If no match exists, it returns false.

Comparisons use the SameValueZero algorithm: like strict equality, but NaN equals NaN. That is a key advantage over indexOf(), which cannot find NaN.

📝 Syntax

General form of Array.prototype.includes:

array.includes(searchElement, fromIndex)

Parameters

• searchElement — the value to look for.
• fromIndex — optional; index to start searching (default 0). Negative values count from the end.

Return value

• true if the element is found at least once.
• false otherwise.
• Original array unchanged.

Common patterns

• arr.includes(42) — basic membership test.
• arr.includes(item, 2) — search from index 2 onward.
• if (tags.includes("js")) { ... } — conditional logic.
• allowed.includes(role) — permission / allow-list checks.

Examples Gallery

Open DevTools Console (F12) or use Try-it labs. Example N maps to ?tryit=N.

const numbers = [1, 2, 3, 4, 5];

console.log(numbers.includes(3));
// true

console.log(numbers.includes(10));
// false

true
false

const mixed = [1, "2", true];

console.log(mixed.includes("2"));
// true

console.log(mixed.includes(2));
// false

true
false

const numbers = [1, 2, 3, 2, 5];

console.log(numbers.includes(2));
// true (found at index 1)

console.log(numbers.includes(2, 3));
// true (found at index 3)

console.log(numbers.includes(2, 4));
// false (search starts at index 4)

true
true
false

const values = [1, NaN, 3];

console.log(values.includes(NaN));
// true

console.log(values.indexOf(NaN));
// -1

true
-1

const allowedRoles = ["admin", "editor", "viewer"];
const userRole = "editor";

if (allowedRoles.includes(userRole)) {
  console.log("Access granted");
} else {
  console.log("Access denied");
}
// Access granted

console.log(allowedRoles.includes("Editor"));
// false (case-sensitive)

Access granted
false

🚀 Common Use Cases

• Permission checks — verify role or feature flags in an allow-list.
• Form validation — ensure selected option is in valid choices.
• Tag filtering — check if a post has a specific tag.
• Game logic — test inventory for an item ID.
• Config guards — skip code paths when env is not in supported list.
• Replacing indexOf — cleaner includes instead of indexOf !== -1.

📝 Notes

• Returns true or false only—not an index.
• Uses SameValueZero (=== plus NaN handling).
• String searches are case-sensitive.
• Objects match by reference, not deep equality.
• For custom logic, use some() with a predicate.
• ES2016—polyfill or indexOf for IE11.

💡 Best Practices