JavaScript .includes()

The .includes() method returns true if a given value is included in an array. Otherwise, it returns false.

Syntax

array.includes(value, index=0);

The following parameters are used:

• A case-sensitive and type-sensitive value that is checked for inclusion in the array.
• An optional index, defaulted to 0, that tells .includes() where to begin the check.

Here are some edge-cases to consider when using .includes():

• It will not work if the provided index is greater than the length of the array. Instead, false will be returned.
• If the index is less than or equal to 0, the entire array will be searched.
• By itself, this method isn’t suitable for nested array and should be used with the .flat() and/or .find() methods.
• For objects, .includes() only returns true for references of the same object (even checking against an object with the same property-value pairs returns false).

Example

The .includes() method can be used in a few ways. First, it can be used directly with an array:

console.log([1, 2, 3].includes(3));
// Output: true

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It can also be used with an array assigned to a variable:

const myArray = [1, '2', 3];

console.log(myArray.includes(2));
// Output: false

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The output above is false because .includes() is type-sensitive. A number-type value 2 was checked for when myArray has no such value. Instead, it has a string literal that reads as ‘2’.

Codebyte Example

The example below uses .includes() on an array, myArray, to check for an object reference, an object literal, and a number.

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