document output function gives blank pdf file

i am trying to output an jspdf document but it gives blank pdf file :

    <script>
        var doc = new jsPDF();
        var img = new Image();
        img.src = 'studentpdf.png';
        var canvas = document.createElement('canvas');
        canvas.width = "210";
        canvas.height = "297";
        canvas.getContext('2d').drawImage(img, 0, 0, 210, 297);
        doc.addImage(canvas.toDataURL('image/png'), 'png',0,0,210,297);
        doc.output('datauri');
    </script>

[TheGreenJaguar]

change the hook line to:

img.addEventListener('load', myFunction, false);

[brmoda]

actually it worked after recode it without the brackets , and i figured out that the png image ( without background ) was the error , when i filled the background with white color it worked !

thank you @TheGreenJaguar for help