Does .bind(this) pass by reference or by value?

Question

I create a function somewhere and I bind it to this so that I can use the parent block's meaning of this as the value of this within the function. For example:

var foo = function() {
    // some stuff involving other stuff
}.bind(this);

Is the this I pass as an argument to bind passed by reference, or by value? So if I change the parameters of the this object a bit later in the outer block of code, and afterwards call foo, will foo use the value of this at the time I called bind, or at the time I called foo?

Answer 1

So if I change the parameters of the this object a bit later in the outer block of code, and afterwards call foo, will foo use the value of this at the time I called bind, or at the time I called foo?

at the time you called foo.

this is a reference to Object. That means Object may get mutated at some point and you will get "fresh - up to date" values of it.

Answer 2

If you will change the value of this object, then foo will get the fresh value of this at the time foo is called.

var module = {
  x: 42,
  getX: function () {
    return this.x;
  }
}

var retrieveX = module.getX;
console.log(retrieveX()); // The function gets invoked at the global scope
// expected output: undefined

var boundGetX = retrieveX.bind(module);
module.x = 52;
console.log(boundGetX());