JS - overwrite this in prototype function

Question

I want to overwrite this in Number prototype function and dynamically change the value of variable, for example:

Number.prototype.xd = function(){
  this = 11212;
}
var a = 171717;
console.log(a);
a.xd();
console.log(a);

is what I want, but it throws an error. In this way works Array.prototype.pop method:

fruits = ["a","b","c","d"];
console.log(fruits);
fruits.pop();
console.log(fruits);

Can I do the same?

Have you ever noticed that all methods for primitive values *return* a new value? — Felix Kling, Jan 09 '17 at 17:06
`Array.prototype.pop` doesn't assign to `this`, it modifies the properties of the object that `this` refers to. — Barmar, Jan 09 '17 at 17:07

nem035 · Answer 1 · 2017-01-10T01:45:49.187

6

You cannot achieve what you want because numbers in JS are immutable.

Another reason why this wouldn't work is because this is already dynamic in JS by its definition so it will automatically change every time a function is called, depending on how it's called.

edited Jan 10 '17 at 01:45

answered Jan 09 '17 at 17:02

nem035

34,790
6
87
99

score 0 · Answer 2 · answered Jan 09 '17 at 17:06

0

That's impossible. The number is one of JS primitives and as all primitives it wraps into Number in runtime.

answered Jan 09 '17 at 17:06

ajile

666
1
10
18

score 0 · Answer 3 · edited May 23 '17 at 10:30

0

You can modify complex types (object, array, function), but unfortunately you can't change primitive types (string, number, boolean, null, undefined). This property is referred to as "immutability".

You may also find this answer helpful: https://stackoverflow.com/a/16115543/3236521

edited May 23 '17 at 10:30

Community

1
1

answered Jan 09 '17 at 17:10

christianbundy

666
9
21

JS - overwrite this in prototype function

3 Answers3