JavaScript Array.isArray() Function – Checking for Arrays

Definition and Usage

The Array.isArray() function is used to check if a given value is an array.

It returns true if the provided argument is an array, and false otherwise.

Basic Example

Syntax

The value parameter is the value to be checked whether it is an array. Returns true if value is an array; otherwise, returns false.

Examples

JavaScript

// All return true
Array.isArray([]);
Array.isArray([1]);
Array.isArray(new Array());
Array.isArray(new Array("a", "b", "c", "d"));
Array.isArray(new Array(3));

// All return false
Array.isArray();
Array.isArray({});
Array.isArray(null);
Array.isArray(undefined);
Array.isArray(17);
Array.isArray("Array");
Array.isArray(true);
Array.isArray(false);

Notes and Considerations

Don't Use the `typeof` Operator to Check for Arrays

The typeof operator returns a string indicating the type of a variable. However, when used on an array, it returns "object". Therefore, you cannot reliably determine whether a value is an array using only typeof

JavaScript typeof Operator – Checking Data Types

For this reason, the most accurate way to check for arrays in JavaScript is to use the Array.isArray() function.

Array-like Objects

avaScript has array-like objects, which resemble arrays but are not actual arrays. Examples include the arguments object and DOM elements like NodeList. The Array.isArray() function returns false for these objects, so be careful when working with them.

JavaScript

function checkArray(arr) {
    if (Array.isArray(arr)) {
        console.log("It is an array.");
    } else {
        console.log("It is not an array.");
    }
}

const argumentsObj = (function() {return arguments;}());
checkArray(argumentsObj); // Output: "It is not an array."