Sproutcore custom getter/setter

In Sproutcore i am using the universal setter/getter method like so:

foo.set('bar', newValue );
val = foo.get('bar');

This is quite different to Objective-c, how would i write a custom ge开发者_JS百科tter/ setter?

EDIT

Thanks to those who helped, the way to do it is

bar: function( propKey, propVal ) {
  if(propVal===undefined) {   // called as getter method
    var computedBarValue = ...
    return computedBarValue;
  } else {
    this.bar = propVal + ...    // called as setter method
  }
}.property()

As you can see, you have one method that is the both the getter and the setter.

if you call

val = foo.get('bar');

the method argument 'propVal' will be undefined.

if you call

foo.set('bar', newValue );

the method argument 'propVal' will be newValue

Custom setter/getter function would look smth like this:

bar: function(key, value){
  if(value != undefined){
    this._bar = value;
  }

  return this._bar;
}

This would simply get/set the value. To do smth on set, just add what you want after this._bar = value, to do smth on get, just add if value == undefined.