A common mistake for new JavaScript programmers is to extract a method from an object, then to later call that function and expect it to use the original object as its this

JSBind

//Varint 1: use bind function https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Function/bind
var val = 1;   
var myObject = {  
  val: 11,
  getVal: function() { return this.val; }  
};  
  
console.log(module.getVal()); // 11
  
var getVal = myObject.getVal;  
console.log(getVal()); // 1, because in this case, "this" refers to the global object  
  
// create a new function with 'this' bound to myObject  
var boundGetVal = getVal.bind(myObject);  
console.log(boundGetVal()); // 11


//Varint 2: alternative to bind function
val = 2;
myObject = {
  val: 22
}

myObject.getVal = function() {
  var that = this;
  var helper = function () {
    console.log(that.val);
  };
  helper();
}

myObject.getVal(); // 22, because although the function is called from the global context, there is a closure in the getVal function in which "that" is bound to myObject