How to Recognize an Array in JavaScript?

The problem is that the JavaScript operator typeof returns “object”:

var numbers = [2, 3, 4]; 

typeof numbers;

//object

Why?

As we have already seen in this post, JavaScript Arrays: A Separate Data Type Or Objects?, JavaScript arrays are objects.

Method 1

We can use Array.isArray() method which was introduced in ECMAScript 5.

var numbers = [2, 3, 4]; 

Array.isArray(numbers);

// true

👎 This method is not supported in older browsers.

Method 2

We can make a our function and use constructor property to know whether it’s an array.

var numbers = [2, 3, 4]; 

function isArray(x) {
  return x.constructor.toString().indexOf("Array") > -1;
}

isArray(numbers);

// true

Let’s understand it.

The constructor property returns an array’s constructor function:

var numbers = [2, 3, 4]; 

console.log(numbers.constructor);

// [Function: Array]

which we convert to a string and get the index of word “Array”. If it’s the array then the word “array” will be there and will return positive value.

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