Decorators.js

Function.implement({
  decorate: function()
  {
    var decorators = $A(arguments);
    var resultFn = this;
    decorator = decorators.pop();
    
    while(decorator)
    {
      resultFn = decorator(resultFn);
      decorator = decorators.pop();
    }
    
    return resultFn;
  }
});

/*
var verify1 = function(fn) {
   return function() {
      var args = $A(arguments);
      if($type(args[0]) != "string")
      {
         throw new Error("First arg is not a string");
      }
      else
      {
         console.log("verify1 decorator run")
         return fn.apply(this, args);
      }
   }
};

var verify2 = function(fn) {
   return function() {
      var args = $A(arguments);
      if($type(args[1]) != "string")
      {
         throw new Error("Second arg is not a string");
      }
      else
      {
         console.log("verify2 decorator run")
         return fn.apply(this, args);
      }
   }
};

// add type checking of first and second arguments to myfn!
var myfn = function(argA, argB) {
  console.log("Hello from myfn! argA " + argA + ", argB " + argB);
}.decorate(verify1, verify2);

// do the same for a class method
var MyClass = new Class({
  name: "MyClass",
  aMethod: function(argA, argB) {
    console.log("Hello from myfn! argA " + argA + ", argB " + argB);
    console.log(this.name);
  }.decorate(verify1, verify2)
});

var instance = new MyClass();
instance.aMethod("foo", "bar"); // works

try
{
  instance.aMethod(2, "bar");
}
catch(err)
{
  console.log(err);
}

try
{
  instance.aMethod("foo", 2);
}
catch(err)
{
  console.log(err);
}

myfn("foo", "bar"); // works

try
{
  myfn(2, "bar"); // verify1 throws exception!
}
catch(err)
{
  console.log(err);
}

try
{
  myfn("foo", 2); // verify2 throws exception!  
}
catch(err)
{
  console.log(err);
}
*/