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includes()

includes<T>(collection, value, fromIndex?): boolean

includes<T>(collection, value): boolean

Checks if value is in collection.

DEPRECATED

Use array.includes() or Object.values().includes() directly instead.

Type Parameters​

T: T​

The type of elements in the array, or the object type.

Parameters​

Overload 1:

collection: T[]​

The collection to inspect.

value: T​

The value to search for.

fromIndex?: number​

The index to search from.

Overload 2:

collection: T​

The collection to inspect.

value: T[keyof T]​

The value to search for.

Returns: boolean​

true if value is found, else false.

See Also​

Since​

2.0.0

Also known as​

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

Example​

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

// ❌ Deprecated approach
const hasThree = includes(numbers, 3);
console.log(hasThree); // true

// ✅ Recommended approach (for arrays)
const hasThreeNative = numbers.includes(3);
console.log(hasThreeNative); // true

// ✅ Recommended approach (for objects)
const obj = { a: 1, b: 2, c: 3 };
const hasThreeObj = Object.values(obj).includes(3);
console.log(hasThreeObj); // true

How it works?​

Checks if value is in collection. Deprecated: Use array.includes() directly (ES2016).

Native Equivalent​

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

Use Cases​

Check element presence 📌​

Check if a value exists in an array.

const roles = ["admin", "moderator", "user"];
roles.includes("admin");
// => true

Validate allowed values​

Check if a value is in an allowlist.

const allowedTypes = ["image/png", "image/jpeg", "image/gif"];
allowedTypes.includes(file.type);

Check string contains substring​

Verify if a string contains a specific substring.

const email = "user@example.com";
email.includes("@");
// => true

Check if a route requires authentication​

Verify if the current route is in a list of protected routes. Fundamental pattern for auth guards in any SPA or server-side routing.

const protectedRoutes = ["/dashboard", "/settings", "/profile", "/admin"];

function requiresAuth(path: string): boolean {
  return includes(protectedRoutes, path);
}

// In a router guard or middleware
if (requiresAuth(currentPath) && !user.isAuthenticated) {
  redirect("/login");
}