Can I use `obj.constructor === Array` to test if object is Array?

Question

Is it correct to use obj.constructor === Array to test if an object is an array as suggested here? Does it always returns correct answer compatible with Array.isArray?

Answer 1

Depends, there are a few scenarios where it can return a different value, but Array.isArray will work.

The Array object for one window is not the the same Array object in another window.

var obj = someIframe.contentWindow.someArray;
console.log(obj.constructor === Array);//false
console.log(Array.isArray(obj));//true

The constructor property can be overwritten.

var obj = [];
obj.constructor = null;
console.log(obj.constructor === Array);//false
console.log(Array.isArray(obj));//true

Another object can also set the constructor property to Array.

var obj = {};
obj.constructor = Array;
console.log(obj.constructor === Array);//true
console.log(Array.isArray(obj));//false