How to Check if Something is an Array?

There are several options to check if something is an array in JavaScript. Here are four known ways to choose from:

// Check the constructor
variable.constructor === Array

The constructor method is a special method of objects, that is used for initialization. You can check whether this is an Array.

// Check if the variable is an instance of Array
variable instanceof Array

You can also use the instanceof operator to test whether your variable is originating from the global Array object.

// Check its prototype
Object.prototype.toString.call(variable) === '[object Array]';

A more verbose way is to call the prototype of the global Object and turning the result into a string, by using your variable as the this argument. If this equals to [object Array], you can be sure you are dealing with an array.

// Use the built-in isArray method
Array.isArray(variable);

Lastly, you can use the built-in isArray method, which expects the variable to check.

So which one to go with? If you can, go withArray.isArray as that is the cleanest and most readable solution. It is also widely supported.

50 JavaScript Interview QuestionsAnd their answers explainedHere are 50 JavaScript interview questions that often come up during a technical interview. In one place, one resource to learn from.Learn More

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Resources:

• isArray method in JavaScript
• instanceof operator in JavaScript
• The constructor method
• Object prototypes