javascript string interpreted as object

Question

Probably irrelevant from a production standpoint, but I'd like to know why this behaves the way it does. The string literal gets interpreted as an object.

function fancyCallback(callback) {
  callback(this);
  console.log(typeof this); // just to see it really is an object
}

fancyCallback.call('string here', console.log);

I have to call

this.toString()

inside the function if I want the expected output. I know strings are objects in javascript (which is lovely) but in a simple console.log('abc'), they are naturally interpreted as strings. Why is that? Is this useful in any way? Please ignore the fact that fancyCallback is defined in the global scope!

I believe it is because of the way variable definitions are in js. — Josef E.
– Josef E., Commented May 1, 2014 at 17:24
console.log() simply calls the toString method on the string — levi
– levi, Commented May 1, 2014 at 17:25
this returns false: (function() {return this;}).call('string here')==='string here' Maybe the object was modified in some way. — simonzack
– simonzack, Commented May 1, 2014 at 17:26
@levi I added console.log(this) to his function, Chrome displayed String {0: "s", 1: "t", 2: "r", 3: "i", 4: "n", 5: "g", 6: " ", 7: "h", 8: "e", 9: "r", 10: "e", length: 11, formatUnicorn: function, truncate: function, splitOnLast: function, contains: function}. — Barmar
– Barmar, Commented May 1, 2014 at 17:26
@levi that is not true, try deleting the typeof keyword inside the function so it says console.log(this). it does not call toString() on it — A. Sallai
– A. Sallai, Commented May 1, 2014 at 17:27

epascarello · Accepted Answer · 2014-05-01 17:34:09Z

6

From MDN call() :

thisArg

The value of this provided for the call to fun. Note that this may not be the actual value seen by the method: if the method is a function in non-strict mode code, null and undefined will be replaced with the global object, and primitive values will be boxed.

Primitives [aka numbers/strings] are placed into a container object, so it is working just like you are seeing it.

So what it is basically doing is

> var x = "string";
> typeof x
"string"
> var temp = new String(x);
> typeof temp
"object"

edited May 1, 2014 at 17:34

answered May 1, 2014 at 17:26

epascarello

208k20 gold badges206 silver badges246 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

A. Sallai Over a year ago

never heard the term "boxed"! honestly, I just love javascript even more for this. thanks!

epascarello Over a year ago

added a little bit more of an explanation

epascarello Over a year ago

OOP Boxing

Collectives™ on Stack Overflow

javascript string interpreted as object

1 Answer 1

3 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related