I'm going to assume that the overall structure of my code as it currently stands is 'best', otherwise this question gets too long, but if I've made any obvious mistakes (or if I've made life hard for myself) then please correct away!

Using jQuery, I have a javascript 'class' set out something like this:

function MyClass () {
  this.noise = "Woof"
  this.dostuff = function() {
    $.getJSON("http://cows.go",function(moo) {
      this.noise = moo.inEnglish;
    }
  }
}

var instance = new MyClass();
instance.doStuff()
console.log(instance.noise)

I'm expecting some kinda tea drinking moo in the console, but of course I'm getting an error about this.noise not being defined (because $.getJSON doesn't pass this through, right?)

Any suggestions as to how to be able to affect instance.squeak for any and all instances of MyClass without interference?