Neat Alternatives To __definegetter__?

Getters and setters are a beauty in VB.Net: Get Return width End Get Set(ByVal value As Integer) width = value End Set In Javascript, this is probably what we would do: fu

Solution 1:

With ES5 you'll be able to do:

function Test() {
  var a = 1;

  return {
    getA() { return a; },
    setA(v) { a = v; }
  };
}

The getter/setter functions can of course do anything you want them to.

Solution 2:

Here's a clean(er) alternative (also for older script engines):

functionTest() {
  var a=1;
  return { A: { toString: function(){return a;} } };
}

alert(Test().A); //=> 1

Mind you, you can't use it to define private/static complex structures. You can only 'get' strings or numbers (so immutable variables) with this pattern. Maybe the pattern can be enhanced using json.

[edit] Using json, you can also create a getter this way for objects:

functionTest() {
  var a=1,
  b = {foo:50, bar:100};

  return { 
          A: { toString: function(){return a;} } 
          foobar: { toString: function(){returnJSON.stringify(b);}  } 
         };
}
var foobar = JSON.parse(Test().foobar);
alert(foobar.foo); //=> 50

Solution 3:

In Ecmascript5, the 'clean' (and standards compliant) way of doing this is with defineProperty.

functionTest() {
    var a = 1;
    Object.defineProperty(this, "A", {get : function() { 
            return a;
        },  
        enumerable : true});
}

This assumes that you just want to see how to define a getter. If all you want to do is make instances of Test immutable (a good thing to do where you can), you should use freeze for that:

functionTest() {
    this.a = 1;
    Object.freeze(this);
}