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!

Answer 1

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"