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 patible with Array.isArray?

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 patible with Array.isArray?

• javascript
• arrays
• types
• prototype

• you can also use the boolean return from "obj instanceof Array", but like your version, it only returns true for an Array of the same window scope. – kennebec Commented Feb 12, 2015 at 1:03
• Do you have read any of the other answers on that question? blog.niftysnippets/2010/09/say-what.html – Bergi Commented Apr 1, 2015 at 20:08
• @Bergi Yes, when I asked this question I was interested to learn more about obj.constructor === Class as well. – Ali Shakiba Commented Apr 1, 2015 at 20:14

1 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