Checking if an object is an Array

Array.isArray(obj) returns true if the object is an Array, otherwise false.

Array.isArray([]) // true
Array.isArray([1, 2, 3]) // true
Array.isArray({}) // false
Array.isArray(1) // false

In most cases you can use instanceof to check if an object is an Array.

[] instanceof Array; // true 
{} instanceof Array; // false

Array.isArray has the an advantage over using a instanceof check in that it will still return true even if the prototype of the array has been changed and will return false if a non-arrays prototype was changed to the Array prototype.

var arr = []; Object.setPrototypeOf(arr, null); 
Array.isArray(arr); // true
arr instanceof Array; // false