Question

Functions nested under a prototype function do not get the this.variables defined for the prototype.

var Person, p;

Person = function(name, age) {
  this.name = name;
  this.age = age;
};

Person.prototype.getInfo = function() {
  var innerFun;
  innerFun = function() {
    return this.name;
  };
  return "name: " + (innerFun()) + " age: " + this.age;
};

p = new Person('dork', 99);

console.log(p.getInfo());      // name:  age: 99

I thought that since every function is an object, this would be different within every function definition; but the following code blows away that logic.

var getInfo;

getInfo = function() {
  var display;
  this.name = 'dork';
  return display = function() {
    return this.name;
  };
};

console.log(getInfo()());     // dork

Is there a logic behind this behaviour or should I just take it as a rule and use call() to get around this problem?

Answer 1

Short version of this behavior:

1. In function invoked as x.f(), this will be x.
   (Note: invoked as x.f(). It does not matter how and where you define it)
2. In function invoked as f(), this will be window.
3. In function invoked as x['f'](), this will be window x (not sure why I thought otherwise)
4. In function invoked as f.call(x) or f.apply(x), this will be x.

Again, the prototype does not matter, if you do

var f = p.getInfo;
console.log(f());

you will see that only calling style matters.