In order to distinguish whether variable is an array or not we have couple of options.

But before we start it is good to mention that arrays in JavaScript are special kind of objects as you can see down bellow:

let testArray = [1, 2, 3];

console.log(typeof testArray); // object

We can check if variable is an array with this code snippet:

let testArray = [1, 2, 3];

console.log(Array.isArray(testArray)); // true

The problem with this solution is that Array.isArray() method is introduced in ECMAScript 5, so if you need support for older browsers you can do something like this by using constructor property:

let testArray = [1, 2, 3];

console.log(testArray.constructor === Array);  // true
console.log(testArray.constructor.name === 'Array');  // true
console.log(testArray.constructor.toString().indexOf('Array') > -1); // true

Also, we are allowed to use instanceof operator:

let testArray = [1, 2, 3];

console.log(testArray instanceof Array); // true

Note:

Although, we can create an array by using new Array() we should prefer way we used in examples above for simplicity, readability and execution speed.

Thank you for reading!