Window.Onload函数未在IE 10中触发

Question

我正在尝试创建一个缩放和平移应用程序，以适用于所有浏览器。它适用于所有其他浏览器，但在IE 10中 - 只是不加载图像，但是当我点击画布放大时重绘它。这是window.onload部分代码：

window.onload = function(){     
    var ctx = canvas.getContext('2d');
    trackTransforms(ctx);
    function redraw(){
    ctx.save();
    ctx.setTransform(1,0,0,1,0,0);
    ctx.clearRect(0,0,canvas.width,canvas.height);
    ctx.restore();
    ctx.drawImage(map,0,0, canvas.width, canvas.height);

    }
    redraw();

    var lastX=canvas.width/2, lastY=canvas.height/2;
    var dragStart,dragged;
    canvas.addEventListener('mousedown',function(evt){
        document.body.style.mozUserSelect = document.body.style.webkitUserSelect = document.body.style.userSelect = 'none';
        lastX = evt.offsetX || (evt.pageX - canvas.offsetLeft);
        lastY = evt.offsetY || (evt.pageY - canvas.offsetTop);
        dragStart = ctx.transformedPoint(lastX,lastY);
        dragged = false;
    },false);
    canvas.addEventListener('mousemove',function(evt){
        lastX = evt.offsetX || (evt.pageX - canvas.offsetLeft);
        lastY = evt.offsetY || (evt.pageY - canvas.offsetTop);
        dragged = true;
        if (dragStart){
            var pt = ctx.transformedPoint(lastX,lastY);
            ctx.translate(pt.x-dragStart.x,pt.y-dragStart.y);
            redraw();
        }
    },false);
    canvas.addEventListener('mouseup',function(evt){
        dragStart = null;
        if (!dragged) zoom(evt.shiftKey ? -1 : 1 );
    },false);

    var scaleFactor = 1.1;
    var zoom = function(clicks){
        var pt = ctx.transformedPoint(lastX,lastY);
        ctx.translate(pt.x,pt.y);
        var factor = Math.pow(scaleFactor,clicks);
        ctx.scale(factor,factor);
        ctx.translate(-pt.x,-pt.y);
        redraw();
    }

    var handleScroll = function(evt){
        var delta = evt.wheelDelta ? evt.wheelDelta/40 : evt.detail ? -evt.detail : 0;
        if (delta) zoom(delta);
        return evt.preventDefault() && false;
    };
    canvas.addEventListener('DOMMouseScroll',handleScroll,false);
    canvas.addEventListener('mousewheel',handleScroll,false);
};
map.src = 'http://www.theodora.com/maps/new9/time_zones_4.jpg';