Different typeof 'this' when calling/applying a strict function vs. a non-strict function

Question

It looks like when I'm using func.call(12) on some non-strict function func, it will use this = new Number(12) instead of this = 12 (see the snippet below). I noticed because typeof this was equal to 'object' instead of 'number'.

Is this expected behaviour? Is there any way around it?

function a() {
  return this;
}

function b() {
  'use strict';
  return this;
}

const x = a.call(12);
console.log(typeof x);
console.log(x);
console.log(x + 3);

const y = b.call(12);
console.log(typeof y);
console.log(y);
console.log(y + 3);

score 2 · Accepted Answer · answered May 27 '18 at 19:20

Is this expected behaviour?

Yes, it's expected behaviour. In sloppy mode, this is always an object - casting primitives to their respective wrapper objects. And worse, null and undefined get replaced with the global object.

Is there any way around it?

Just always use strict mode.

Different typeof 'this' when calling/applying a strict function vs. a non-strict function

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