1 /*
 2   interface  composite{
 3     function add(child);
 4     function remove(child);
 5     function getChild(index);
 6   }
 7   interface FormItem{
 8     function save();
 9   }
10 */
11 var CompositeForm = function(){
12     ...
13 }
14
15 CompositeForm.prototype = {
16     add: function(child){...},
17     remove: function(child){...},
18     getChild: function(index){...},
19     save: function(){...}
20 }

/*interface  composite{function add(child);function remove(child);function getChild(index);}interface FormItem{function save();}
*/var CompositeForm = function(){this.implementsInterfaces = ['Composite','FormItem'];...}function addForm(formInstance){if(! implements(formInstance,'Composite','FormItem')){throw new Error('object does not omplement a required interface');}...}function implements(object){for(var i=1;i<arguments.length;i++){var interfaceName = arguments[i];var found = false;for(var j=0;j<object.implementsInterfaces.length;j++){if(object.implementsInterfaces[j] === interfaceName){found = true;break;}}if(! found){return false;   //an interface was not found
        }}return true;
}

 1 var Interface = function(name,methods){
 2     if(arguments.length != 2){
 3         throw new Error('....');
 4     }
 5     this.name = name;
 6     this.methods = [];
 7     for(var i=1; i< methods.lenght;i++){
 8         if(typeof method[i] !== 'string'){
 9             throw new Error(...);
10         }
11         this.methods.push(methods[i]);
12     }
13 }
14 Interface.ensureImplements = function(object){
15     if(arguments.length < 2){
16         throw new Error(...);
17     }
18     for(var i=1;i<arguments.lenght;i++){
19         var interfaceName = arguments[i];
20         if(interfaceName.constructor !==Interface){
21             throw new Error(...);
22         }
23         for(var j=0; j<interfaceName.methods.length;j++){
24             var method = interfaceName.methods[j];
25             if(!object[method] || typeof object[method] !== 'function'){
26                 throw new Error(...);
27             }
28         }
29     }
30 }

 1 /*
 2   interface  composite{
 3     function add(child);
 4     function remove(child);
 5     function getChild(index);
 6   }
 7   interface FormItem{
 8     function save();
 9   }
10 */
11 var Composite = new Interface('Composition',['add','remove','getChild']);
12 var FormItem = new Interface('FormItem',['save']);
13
14 var CompositeForm = function(){
15     ...
16 }
17
18 function addForm(formInstance){
19     Interface.ensureImplements(formInstance,Composite,FormItem);
20     ...
21 }