JavaScript design mode 15th Observer pattern-Learning notes

definition:

In an event-driven environment, such as a browser that continues to seek user attention, the Observer pattern (aka Publisher-subscriber "Publisher-subscriber" mode) is a relationship between the manager and his or her task (specifically, the relationship between its object and its behavior and state).

) is a powerful tool. In JavaScript, the essence of this pattern is that you can observe the state of an object in the program and be notified when it changes.

Viewer API:

var publisher=function() {this. subscribers=[];} Push method Publisher.prototype.deliver=function(data) {          this. Subscribers.foreach (function(FN) {                                       fn (data);                                                })                          return  This ;                      };

Subscription Method:

Function.prototype.subscribe=function(publisher) {varself= This; varAlreadyexists=publisher.subscribers.some (function(value) {returnValue = =Self ;          }                                               ); if(!alreadyexists) {Publisher.subscribers.push ( This); }            return  This ;};

Here's an episode where the translator adds the following code:

"Since any of the functions are instances of function, the new methods added in Function.prototype are inherited by all functions." Of course, adding subscribe to the Function.prototype is just for the sake of convenience and should not be done in the actual project. "

So what should I do? I couldn't help but ask.

var    subscribe=function

   var alreadyexists=publisher.subscribers.some (function (value) {                return  value ===self;             }          );          if (!alreadyexists) {                          Publisher.subscribers.push (this);            }

                             

                                         (1)

function C (a) {alert (a+3)}

 var publisher= new publisherSubscribe . Call (A,publisher) (2)

Wow, that's all you can do. What a coincidence!!

Unsubscribe method:

function.prototype.unsubscribe=function(publisher) {                                         var self=this; Publisher.subscribers=publisher.subscribers.filter (function(value) {                                   return   value!== self;                                             }                                        );                             return  This  ;                           };

This, of course, can also be a form of the above function (1) (2):

var   unsubscribe=function
  

  publisher.subscribers= Publisher.subscribers.filter (function(value) {                  returnself  ;                                               }                                         )                         ;                                                 (3)function C (a) {alert (a+3)}       varnew  Publisher Unsubscribe.call (A,publisher)                   (4)

The OK observer pattern is roughly what it looks like ...

JavaScript design mode 15th Observer pattern-Learning notes