Javascript: onload function called twice

Question

Transition.start = function(){
    for(var j = 0; j < 6; j++)
    {
         console.log("FOR LOOP");
         (function(){
             console.log("INNER Function");
             var image = new Image();
             image.src = path + Config.imgName[j] + ".jpg";
             image.onload = function () {

                 console.log("GONE");
                 clearImages[source].push(image);
                 console.log(image);
             };
         })();
     }
}

In this on console "FOR LOOP" and "INNER Function" is printed 6 times, but "GONE" is printed 12 times. I am not able to figure out the reason for this. I want to run the body of onload also 6 times.

and Transition.start is called from onDocumentKeyDown listener like this

function onDocumentKeyDown( event )
{
    if (keyPressed == 38) //up arrow
        Transition.start();
}

I think console.log(image) is calling the "image.onload" and hence the "GONE" is being print more number of times. — Alekhya Vemavarapu
– Alekhya Vemavarapu, Commented Jun 10, 2015 at 9:56

ViliusL · Accepted Answer · 2017-11-21 19:50:27Z

13

I got the the source of the problem. Actually image.onload is called everytime the image is rendered in the browser. Actually I once image is loaded I was storing it in clearImages so that if in future the image is required then it can be taken directly from that array, so if the image is required in future then it is loaded from the clearImages array but again the onload function will be called.

So I solved this thing by doing image.onload = null inside onload function itself

edited Nov 21, 2017 at 19:50

ViliusL

4,80629 silver badges29 bronze badges

answered Jul 2, 2015 at 10:24

Saurabh Kathpalia

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