Is your object an array?

Jun 5, 2023 • 1 min read

Whenever we want to check if an object we’ve passed into a function is an array, we conveniently have the Array.isArray() function.

However, suppose that you’re trapped in some situation where you cannot use the above function to determine if an object is an array. How can we reason about this?

You can probably assume that you can do something like typeof array but it turns out this won’t work because you’ll get an object.

So what are some actual ways we can determine if your object is an array?

instanceof

We can use the instanceof keyword to determine if an array is an Array. So we can do something like

[1, 2, 3] instanceof Array;

Object.prototype.toString.call()

Another way of figuring out if an object is an array is by calling toString on the object

Object.prototype.toString.call([1, 2, 3]); // [Object array]