CODEWITHSUNDEEP
javascript
Alex Cube
Alex Cube

Reputation: 53

javascript singleton -- is this correct

I'm writing javascript singleton class and want to use singleton pattern like this:

function TestClass() {
    var self = TestClass.prototype;
    if (self.instance) return self.instance;
    self.instance = this;

    //methods and props declarations
}

var x = new TestClass;
var y = new TestClass;

console.log(x === y); // true

It seems to be worked as i expected, but i worry about memory leaks. So i decided to ask experts, if it is the correct solution

Upvotes: 2

Views: 282

Answers (2)

Peter Aron Zentai
Peter Aron Zentai

Reputation: 11740

Your code is not wrong per se but not good either. you are not creating a singleton, just "hijack" the prototype. #svidgen gave a correct response.

Upvotes: 0

svidgen
svidgen

Reputation: 14302

Not exactly. I generally do something like this when I need a singleton:

function TestClass() {
  if (TestClass.__singleton) {
    return TestClass.__singleton;
  }

  // begin construction ...

  this.a = function() { };
  this.b = 1;

  // ... end construction

  TestClass.__singleton = this;

} // TestClass

var x = new TestClass();  // creates a new TestClass and stores it
var y = new TestClass();  // finds the existing TestClass

console.log(x === y);  // true

y.b = 2;
x.c = 3;

console.log(x.b === y.b && x.c === y.c); // true

If my understanding is correct, subsequent TestClass instantiations, in this case, will create a small, partially-defined TestClass object, but will immediately mark them for garbage collection when TestClass.__singleton is returned.

Upvotes: 1

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