MUTABLE.JS
Mutable.js is a Javascript Getter/Setter Class with support for binding, locking and property watching.
SUPPORT
Mutable.js is supported by Firefox, Internet Explorer, Safari and Opera (version 10+)
USAGE
Include Mutable.js to your page
DEFINING
--------------- JAVASCRIPT --------------
  var object =
  {
    // a variable that convert its assigned value to interger.
    a: new Mutable({
      value: 0,
      setter: function(value)
      {
        this.value = parseInt(value);
      }
    }),
    
    // get a and multiple it by two
    b: new Mutable({
      getter: function()
      {
        return this.parent.a() * 2;
      }
    })
  };
-----------------------------------------
BINDING
--------------- JAVASCRIPT --------------
  var a = {};
  a.value = new Mutable({
    value: 0,
    setter: function(x)
    {
      this.value = x;
      alert(x);
    }
  });
  
  var b = {};
  b.value = new Mutable({value:1});
  
  var c = {};
  c.value = new Mutable({value:10});
  
  a.value.bind(function(){
    return b.value() * c.value();
  });
  // Alert 10
  
  b.value(2);
  // Alert 20
  
  c.value(20)
  // Alert 40
  
  a.value.unbind();
  
  c.value(15);
  // no alert
-----------------------------------------
LOCKING
--------------- JAVASCRIPT --------------
  var a = {value: new Mutable({value:0})};
  
  function fn1(){a.value(1);};
  function fn2(){a.value(5);};
  function fn3(){a.value(10);};
  
  a.lock(fn1, fn3);
  
  fn1() // a.value = 1
  fn2() // a.value = 1
  fn3() // a.value = 10
  
  a.lock(fn2); // can't modify lock again
  fn2() // a.value = 10
-----------------------------------------
LOCKING
--------------- JAVASCRIPT --------------
  var a = {value: new Mutable({value:0})};
  
  function fn(oldval, newval){
    alert('a.value changed from ' + oldval + ' to ' + newval);
  }
  
  a.watch(fn);
  
  a.value(1); // alert: a.value changed from 0 to 1
  a.value(1); // no alert
  a.value(10); // alert: a.value changed from 1 to 10
  
  a.value.unwatch(fn);
  
  a.value(12); // no alert
  
-----------------------------------------