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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: singleton

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. Both comments and pings are currently closed.