CODEWITHSUNDEEP
javascript
php_nub_qq
php_nub_qq

Reputation: 16055

Javascript: destructor or something like that

I've created this little object that's pretty handy when it comes to intervals and works pretty good as an animation frame, but it has this little thing about it. If the reference to the instance is lost, the interval keeps going.

function Interval(callback, interval){
    var timer = null;
    this.start = function(){
        if(!timer) timer = setInterval(callback, interval);
    };
    this.stop = function(){
        clearInterval(timer);
        timer = null;
    };
    this.changeSpeed = function(a){
        interval = a;
        this.stop();
        this.start();
    }
    this.destroy = function(){
        delete this;
    }
}

Obviously if javascript has no destruct method I can't track when to stop the interval, so I figured I should create a destroy method, but I'm not really sure if I can destroy the instance from within the object. It makes sense but... Any help is appreciated!

Upvotes: 4

Views: 2847

Answers (1)

Matt Burland
Matt Burland

Reputation: 45155

How about doing something like this:

function Interval(callback, interval){
    var self = this;
    var timer = null;
    this.start = function(){
        if(!timer) timer = setInterval(function() {
            callback(self)
        }, interval);
    };
    this.stop = function(){
        clearInterval(timer);
        timer = null;
    };
    this.changeSpeed = function(a){
        interval = a;
        this.stop();
        this.start();
    }
    this.destroy = function(){
        this.stop();
    }
}

Now at least when the callback is called it will pass a reference to the your object and the callback will at least have a chance to stop it if they don't need it anymore.

The trick here is to use a closure to ensure you can still reference the object when the interval expires (hence the self variable).

So now I could do something like this:

var foo = new Interval(function(i) {
     // check if my interval is still needed
     if (dontNeedItAnymore) {
         i.destroy();        // or just .stop()
     }
     else {
         // do whatever
     }
}, 1000);

foo = null;       // whoops, lost the reference, but the callback will still be able to reference it

Upvotes: 2

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