The arguments.callee Debate
OK, I'll admit I can sometimes be "late to the game" on some things. Specifically, I realize that the whole arguments.callee/singleton design pattern/deprecation in Javascript debate is about two years old. However, I think this is one of those things that generally is worth mentioning (and consequently giving more fuel and attention to).
As many of you know, I started a new gig at VEVO this past June as a web developer. In other words, I'm moving away from Actionscript and more towards Javascript. Don't get me wrong; I'm still true to my AS3/PHP/OOP roots but JS is where it's at right now so I needed to make a change. One of the things I needed to figure out first is how to convert my design patterns over to JS, specifically the infamous Singleton. Given the fact that JS is a loosely typed language, this wasn't going to be easy.
After much research, I created the following example:
function SingletonClass(nme,clr){ if (arguments.callee.instance){return arguments.callee.instance;} arguments.callee.instance = this; this.name = nme; this.color = clr; } SingletonClass.prototype.setColor = function(clr){ this.color = clr; } SingletonClass.prototype.setName = function(nme){ this.name = nme; } var singleton1 = new SingletonClass('firstSingleton','black'); console.log('(singleton1): My name is ' + singleton1.name + ' and my color is ' + singleton1.color + '.'); var singleton2 = new SingletonClass('secondSingleton','green'); console.log('(singleton2): My name is ' + singleton2.name + ' and my color is ' + singleton2.color + '.'); singleton2.setColor('blue'); singleton2.setName('Matt'); console.log('(singleton1): My name is ' + singleton1.name + ' and my color is ' + singleton1.color + '.');
This works beautifully, with one small exception; arguments.callee has been deprecated. If you're like me, you're immediately thinking, "WHAT?????" right about now. After a bit of research, I found the following but reports:
https://bugzilla.mozilla.org/show_bug.cgi?id=725398
https://bugs.ecmascript.org/show_bug.cgi?id=263
However, this doesn't solve the problem. The fact is, currently this is deprecated so if you want to create a true Singleton, a bit of adjustment is necessary. Given that, I came up with the following:
var SingletonInstance; function SingletonClass(nme,clr){ if(SingletonInstance){return SingletonInstance;} SingletonInstance = this; this.name = nme; this.color = clr; } SingletonClass.prototype.setColor = function(clr){ this.color = clr; } SingletonClass.prototype.setName = function(nme){ this.name = nme; } var singleton1 = new SingletonClass('firstSingleton','black'); console.log('(singleton1): My name is ' + singleton1.name + ' and my color is ' + singleton1.color + '.'); var singleton2 = new SingletonClass('secondSingleton','green'); console.log('(singleton2): My name is ' + singleton2.name + ' and my color is ' + singleton2.color + '.'); singleton2.setColor('blue'); singleton2.setName('Matt'); console.log('(singleton1): My name is ' + singleton1.name + ' and my color is ' + singleton1.color + '.');
Yes, this is not necessarily the same thing but if you run it, you'll see that it does indeed accomplish the same goal. I wanted to share this so that others who are looking for a Javascript Singleton pattern "starter kit" can hopefully use my work as a launch pad.