gistfile1.js

Object.prototype.sayHello = function()
{
  console.log("YOU FAIL");
}

Object.prototype.setAttributes = function(attributes)
{
  for(var attName in attributes)
  {
    this[attName] = attributes[attName];
  }
}


var helloer = {
  helloString: "HELLO!",
  sayHello: function(){
    console.log(this.helloString);
  }
}

helloer.sayHello();
// Prints "HELLO!" as expected

helloer.setAttributes({helloString: "GOODBYE"});

helloer.sayHello();
// Prints "YOU FAIL" instead of "GOODBYE"