var element = document.getElementById('element');

​

var user = {

 firstname: 'Bob',

 greeting: function(){

   alert('My name is ' + this.firstname);

 }

};

​

// Overwrite the original function with

// a new function with its execution

// context 'bound' to the user object

user.greeting = user.greeting.bind(user);

​

// Add the bound function as the callback

element.addEventListener('click', user.greeting);