CODEWITHSUNDEEP
javascript
Elian
Elian

Reputation: 447

Make sure this refers to the object

I have the following object:

dog = {
  location: {
    x: 52.1089,
    y: 16.2323
  },
  f: function(message) {
    alert(message + this.location.x);
    return;
  }
};

Now I need to start passing the function dog.f to an API in different contexts. My problem is that this not always refers to my object but to different things depending on how it is called. How can I access properties like location inside the function f?

EDIT: What I actually want is only the method fbut I dont want to initialize location inside f on each function call, so I thought an object would be the best idea. This was my first attempt:

var f = function(message) {
    var location: {
      x: 52.1089,
      y: 16.2323
    }
    alert(message + location.x);
    return;
  }

but it looks wasteful to initialiaze location on every function call.

EDIT 2: I am open for a coffeescript solution

Upvotes: 0

Views: 44

Answers (3)

RobG
RobG

Reputation: 147343

You might consider using a closure (see Private Members in JavaScript):

var dog = (function() {
  var location = {x: 52, y:16};
  return {
    getLocation: function() {
      return [location.x, location.y];
    },
    setLocation: function (newX, newY) {
      location.x = newX;
      location.y = newY;
    },
    showMessage: function(message) {
      alert(message + location.x);
    }
  };
}());

dog.showMessage('here : ');

Upvotes: 2

Parag Bhayani
Parag Bhayani

Reputation: 3330

You probably want to do this

var Dog = function() {
  this.location = {
    x: 52.1089,
    y: 16.2323
  };
  this.f = function(message) {
    alert(message + this.location.x);
    return;
  }
};

var dogObj = new Dog();

dogObj.f("Hellow World!");

Upvotes: 0

Guffa
Guffa

Reputation: 700152

You can use the bind method to set the context for the method:

var func = dog.f.bind(dog);

When you call func from anywhere, it will have the same context as if it was called as dog.f.

Note: The bind method isn't supported in older browsers, for example IE 8 and older, so you would need a 'polyfill' if you need to support those. There is one in the documentation that I linked to.

Upvotes: 4

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