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JavaScript Decorator Pattern

Question:

I am trying to get a decorator pattern to work follwing

<a href="http://www.joezimjs.com/javascript/javascript-design-patterns-decorator/" rel="nofollow">http://www.joezimjs.com/javascript/javascript-design-patterns-decorator/</a>

I might have missed some point but the pattern does not work as i expect.

If i add two decorators and add them to a class the functions are not passed through as i thought. Only the last decorator's functions can be called or the basic Decorator is called. The chaining is broken. How do i fix this?

I added a fiddle:

<a href="http://jsfiddle.net/hbyLW/25/" rel="nofollow">http://jsfiddle.net/hbyLW/25/</a>

UPDATE: Corrected Version

<a href="http://jsfiddle.net/hbyLW/29/" rel="nofollow">http://jsfiddle.net/hbyLW/29/</a>

And the source code:

// A basic device class var device = function(options) { this.brightness = options.brightness; this.Id = options.Id; this.motion = options.motion; }; // Adding some functions to the class device.prototype = { getID: function() { console.log("This ID:" + this.device.Id); return this.Id; }, getBrightness: function() { console.log("This Brightness: " + this.brightness); return this.brightness; }, getMotion: function() { console.log("This Motion: " + this.motion); return this.motion; } }; // A device Decorator var deviceDecorator = function(device) { this.device = device; }; // Adding pass through functions to the Decorator deviceDecorator.prototype = { getId: function() { console.log("Old Id"); return this.device.getId; }, getBrightness: function() { console.log("Old Brightness"); return this.device.getBrightness; }, getMotion: function() { console.log("Old Motion"); return this.device.getMotion; } }; // A Decorator that adds some functionality to the getBrightness function var brightnessDecorator = function(device) { deviceDecorator.call(this, device); }; brightnessDecorator.prototype = new deviceDecorator(); brightnessDecorator.prototype.getBrightness = function() { this.device.getBrightness(); console.log("Changed Brightness"); }; var motionDecorator = function(device) { deviceDecorator.call(this, device); }; // A Decorator that adds some functionality to the getMotion function motionDecorator.prototype = new deviceDecorator(); motionDecorator.prototype.getMotion = function() { this.device.getMotion(); console.log("changed Motion"); }; // Some options for a device var options = { Id: "Identifier", brightness: true, motion: false }; // Create a new device var Lamp = new device(options); // Add the decorators to the device Lamp = new brightnessDecorator(Lamp); Lamp = new motionDecorator(Lamp); // Executing the functions Lamp.getId(); Lamp.getMotion(); Lamp.getBrightness(); console.log(Lamp);?

Answer1:

Your first decorator returns device.getID (the function itself) rather than calling it and returning the value it returns.

deviceDecorator.prototype = { getID: function() { console.log("Old Id"); return this.device.getID(); // <= call function instead of returning it }, ... }

Also, make sure your capitalization is consistent.

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