var sum = add(3, 4); //sum is 7 When a function is invoked with this pattern, "this" is bound to the global object. If the methods defines a variable and assigns it the value of "this", the inner function will have access to "this" through that variable. By convention, the name of that variable is "that". This text and example was taken from the…

the_function_invocation_pattern.js

//Augment myObject with a double method.

add = function(a, b){ return a + b; };
  
var myObject = { value: 0 };

myObject.double = function( ){
  var that   = this; //Workaround
  
  var helper = function( ){ that.value = add(that.value, that.value); };
  
  helper( ); //Invoke helper as a function
};

console.log(myObject.value); //Show 0

myObject.value = 2;
myObject.double( );

console.log(myObject.value); //Show 4