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Singleton without a closure

Warning: anti-pattern ahead.

Mwahaha, I feel like a ninja. I mean a ninja by Doug Crockford's definition which means someone who finds a mistake in the language's design, decides it's cool and abuses it.

So there you go. Regular expression objects are created only once if you're using a literal. Such an object can be used to store the single instance of a Singleton() constructor.

Implementation

function Single() {
    "strict me not!";

    var re = / /;
    if (re.instance) {
        return re.instance;
    }
    re.instance = this;
    this.name = "Foo";

}

Single.prototype.getName = function () {
    return this.name;
};

Test

var s1 = new Single(),
    s2 = new Single();

console.log(s1 === s2); // true
console.log(s1.getName()); // "Foo"
s1.name = "dude";
console.log(s2.getName()); // "dude"

Pros

  • The prototype chain works fine
  • No closures
  • No public properties or globals to store the single instance

Cons

  • It's a hack
  • ES5 defines that reg exp literals should no longer work like this

Verdict

Don't use. Please :)

Tags:

This entry was posted on Saturday, July 17th, 2010 and is filed under Object creation patterns. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

4 Responses to “Singleton without a closure”

  1. Balázs Galambosi Says:
    July 18th, 2010 at 5:54 am

    Lol. Why not:


    function Single() {
    "strict me not!";

    if (Single.instance) {
    return Single.instance;
    }
    Single.instance = this;
    this.name = "Foo";
    }

  2. jdalton Says:
    July 18th, 2010 at 2:50 pm

    At least IE, Safari, and Opera all fail this pattern because they evaluate the literal each time. Balázs’ suggestion is better.


    var Single = (function() {
    function Klass() { };
    function Single(name) {
    one.name = name || 'Foo';
    return one;
    }
    var one = new Klass;
    Single.prototype = Klass.prototype;
    return Single;
    })();

    Single.prototype.getName = function () {
    return this.name;
    };

    The it works cross-browser, the instance isn’t stored as an external property, and it allows `Single` to work when called as function or a constructor.

  3. jdalton Says:
    July 18th, 2010 at 3:06 pm

    For a flavor more in line with the pattern you are trying to achieve:


    var Single = function(name) {
    function Klass() { };
    function Single(name) {
    name && (one.name = name);
    return one;
    }
    Single.prototype = Klass.prototype = window.Single.prototype;
    window.Single = Single;
    var one = new Klass;
    return Single(name);
    };

    Single.prototype.name = 'Foo';

    Single.prototype.getName = function () {
    return this.name;
    };

  4. Takaful Keluarga Says:
    December 18th, 2011 at 3:53 am

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