传递方法时访问javascript实例成员

Question

I wrote some code like this

function Flasher() {
    this.cards = []
    this.map = {
        14: this.flip
    }
}
Flasher.prototype.flip = function() {
    alert(this.cards.length)
}
flasher = new Flasher()
flasher.map[14]()

Unfortunatley, the this object becomes the map object within the flip method and an error occurs (because cards is undefined).

How can I get this to function as intended? Calling flip indirectly via map is necessary, but I would like access to the original object within flip .

Answer 1

function Flasher() {
    var self = this;

    this.cards = [];
    this.map = {
        14: function() { self.flip(); }
    };
}

Answer 2

Ah the hassles of the protoype pattern

I would rewrite it as a module like so:

function flasher() {
  var cards = [],
  flip = function (){
    alert(cards.length)
  },
  map = {
    14: flip
  };

  return {
    cards: cards,
    map: map,
    flip: flip
  };
}

Then the closure captures your scope and you never need to worry about this . You lose a bit of memory though as your flip function is replicated for each object. But I think the code is a lot cleaner and it allows for private variables.