JavaScript loop/scope issue with Image.onload()

问题:

I'm trying to loop through an object with JavaScript and add all the subobjects from that object to a HTML5 canvas.

The canvas-bit is working, no problem with that, but for some reason all my images end up being the same size - the size of the last subobject 'background'. I'm assuming that it has to do with the scope of my loop and 'this', but I can't really see what to change;

var stage;
var items = {
    head: {image: null, path: "images/avatar-elements/head01.png", w:200, h:200},
    hair: {image: null, path: "images/avatar-elements/hair01.png", w:200, h:200},
    nose: {image: null, path: "images/avatar-elements/nose01.png", w:200, h:200},
    eyes: {image: null, path: "images/avatar-elements/eyes01.png", w:200, h:200},
    eyebrows: {image: null, path: "images/avatar-elements/eyebrows01.png", w:200, h:200},
    ears: {image: null, path: "images/avatar-elements/ears01.png", w:200, h:200},
    background: {image: null, path: "images/avatar-elements/background01.png", w:500, h:370}
};

function initCanvas() {
    stage = new Kinetic.Stage("canvas", 500, 370);
    makeBasis();
}


function makeBasis() {
    for(i in items) {
        var img = new Image();
        img.onload = function() {
            items[i].image = makeCanvasImage(this, items[i].w, items[i].h);
        }
        img.src = items[i].path;
    }


}

function makeCanvasImage(tar, w, h) {
    var theImage = new Kinetic.Image({
        imageObj: tar,
        x: 250 - (w / 2),
        y: 185 - (h / 2),
        width: w,
        height: h
    });
    stage.add(theImage);
    return theImage;
}

initCanvas();

回答1:

Bug is in makeBasis(). After looping on all images i is set to last - classic closure problem. Try to use this:

function makeBasis() {
    for(i in items) {
        var img = new Image();
        img.onload = (function (nr) {
            return function() {
                items[nr].image = makeCanvasImage(this, items[nr].w, items[nr].h);
            }
        }(i));      
        img.src = items[i].path;
    }
}