Function Prototypes

Adding a prototyped method to a function.

 function Ninja(){} 
  
 Ninja.prototype.swingSword = function(){ 
   return true; 
 }; 
  
 var ninjaA = Ninja(); 
 assert( !ninjaA, "Is undefined, not an instance of Ninja." ); 
  
 var ninjaB = new Ninja(); 
 assert( ninjaB.swingSword(), "Method exists and is callable." ); 

Properties added in the constructor (or later) override prototyped properties.

 function Ninja(){ 
   this.swingSword = function(){ 
     return true; 
   }; 
 } 
  
 // Should return false, but will be overridden 
 Ninja.prototype.swingSword = function(){ 
   return false; 
 }; 
  
 var ninja = new Ninja(); 
 assert( ninja.swingSword(), "Calling the instance method, not the prototype method." );

Prototyped properties affect all objects of the same constructor, simultaneously, even if they already exist.

 function Ninja(){ 
   this.swung = true; 
 } 
  
 var ninjaA = new Ninja(); 
 var ninjaB = new Ninja(); 
  
 Ninja.prototype.swingSword = function(){ 
   return this.swung; 
 }; 
  
 assert( ninjaA.swingSword(), "Method exists, even out of order." );
 assert( ninjaB.swingSword(), "and on all instantiated objects." ); 

QUIZ: Make a chainable Ninja method.

 function Ninja(){ 
   this.swung = true; 
 } 
  
 var ninjaA = new Ninja(); 
 var ninjaB = new Ninja(); 
  
 // Add a method to the Ninja prototype which
 // returns itself and modifies swung
  
 assert( !ninjaA.swing().swung, "Verify that the swing method exists and returns an instance." );
 assert( !ninjaB.swing().swung, "and that it works on all Ninja instances." ); 

The chainable method must return this.

 function Ninja(){ 
   this.swung = true; 
 } 
  
 var ninjaA = new Ninja(); 
 var ninjaB = new Ninja(); 
 
 Ninja.prototype.swing = function(){
   this.swung = false;
   return this;
 }; 
  
 assert( !ninjaA.swing().swung, "Verify that the swing method exists and returns an instance." );
 assert( !ninjaB.swing().swung, "and that it works on all Ninja instances." ); 

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