Bound function as a method
الأهمية: 5
What will be the output?
function f() {
  alert( this ); // ?
}
let user = {
  g: f.bind(null)
};
user.g();
        The answer: null.
function f() {
  alert( this ); // null
}
let user = {
  g: f.bind(null)
};
user.g();
        The context of a bound function is hard-fixed. There’s just no way to further change it.
So even while we run user.g(), the original function is called with this=null.