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JavaScript JavaScript Foundations Functions Return Values

Posted by Simon Kassa
Simon Kassa
3,558 Points

What is the recommended/standard way of identifying arrays from other type of objects?

I came across a post on stackoverflow on the topic of checking if an object is an array. Some of the discussion posts were specific to arrays and others were general object identification. I want to know if there is a recommended way of identifying arrays or other objects?

Link: http://stackoverflow.com/questions/4775722/check-if-object-is-array

5 Answers

Michael Liquori
Michael Liquori
8,131 Points
Michael Liquori
Michael Liquori
8,131 Points

According to MDN it seems to be:

Array.isArray(my_array) === true/false
J Scott Erickson
J Scott Erickson
11,883 Points
J Scott Erickson
J Scott Erickson
11,883 Points

typeof will give you a returned string to compare against for simple data types (strings, integers). Array is different. This works for example:

var arr = ["this","and","that"];

if ( arr instanceof Array ) {
  console.log("Yep, thats an array");
} else {
  console.log("Nope, thats not an array");
}
Arthur Verschaeve
Arthur Verschaeve
20,816 Points
Arthur Verschaeve
Arthur Verschaeve
20,816 Points

I'm not a huge fan of using the instanceof operator for this, since it doesn't work with Array-Like Objects. Also, since array isn't a datatype something with typeof won't work.

I personally prefer using something like this function (grabbed from the jQuery source code)

J Scott Erickson
J Scott Erickson
11,883 Points
J Scott Erickson
J Scott Erickson
11,883 Points

I'd agree that this is the better way if you are using the jquery library in your project.

Arthur Verschaeve
Arthur Verschaeve
20,816 Points

You don't have to be using jQuery for that, it's like one function that you can just copy.

Faddah Wolf
Faddah Wolf
12,811 Points
Faddah Wolf
Faddah Wolf
12,811 Points

i'm with Michael Liquori above ^^^^. per MDN it's Array.isArray().

ā€” faddah portland, oregon, u.s.a.

diannalord
diannalord
7,284 Points
diannalord
diannalord
7,284 Points

longer version

    function isArray(myArray) {
        return myArray.constructor.toString().indexOf("Array") > -1;
    }