Function
JavaScript functions are objects. They can be defined using the Function constructor, like so:
    var sum = new Function('a', 'b', 'return a + b;'); 
This is a (generally not recommended) alternative to the function literal (also known as function expression):
    var sum = function (a, b) { 
      return a + b; 
    }; 
Or, the more common function definition:
    function sum(a, b) { 
      return a + b; 
    } 
The Function.prototype members
Following are the list of members of the Function constructor:
| 
 Property/Method  | 
 Description  | 
| 
 
  | 
 Allows you to call another function while overwriting the other function's      function whatIsIt(){   
      return this.toString();   
    }   
    > var myObj = {};   
    > whatIsIt... |