I found this code, to add before and after the ability to run a function, searched and don't know, what is new(self) mean there?

Function.prototype.before = function(fn) {
  const self = this
  return function() {
    fn.apply(new(self), arguments)
    return self.apply(new(self), arguments)
  }
}
Function.prototype.after = function(fn) {
  const self = this
  return function() {
    self.apply(new(self), arguments)
    return fn.apply(new(self), arguments)
  }
}


...


const validate = function(){
  // ...
}
const formSubmit = function() {
  // ...
  ajax( 'http:// xxx.com/login', param )
}
submitBtn.onclick = function() {
  formSubmit.before( validate )
}