Accessing prototype value from object Literal

Question

I have tried hard looking for a solution for this issue, found kind of strange that this question wasn't asked before here:

    var A = function(){
    this.timeLength = 5;
    }
    A.prototype.info = {
    type: 'video',
    duration: function(){ return this.timeLength;}
    }

    var AInst = new A();
    AInst.info.duration(); // is giving undefined

How to write this in the way to make it access the instance property?

Answer 1

A couple of things here:

1. Typo on AInst and duration.
2. The this.timelength in your duration method is referring to A.prototype.info , not A.prototype

That being said, you could change your code by either invoking AInst.info.duration() on the last line, or just assign .type and .duration to A.prototype :

var A = function(){
  this.timeLength = 5;
}
A.prototype = {
  type: 'video',
  duration: function(){ return this.timeLength;}
}

var AInst = new A();
AInst.duration();

Answer 2

'this' is wherever 'this' is called. so... function(){ this } 'this' is the function. You could use the window object. If needed, you can pass a 'this' as an argument to another function... just don't call it 'this'... that'll get ugly fast. 'self' is a common name for copies of a 'this'

window.onload = doThis;
function doThis() {
  var A = function(){
  window.timeLength = 5;
  }
  A.prototype.info = {
  type: 'video',
  duration: function(){ return window.timeLength;}
  }

  var AInst = new A();
  AInst.info.duration(); // is giving undefined

  console.log(AInst.info.duration());
}