jQuery如何实现预加载图片功能

function preloadImg(list,imgs) {

    var def = $.Deferred(),

        len = list.length;

    $(list).each(function(i,e) {

        var img = new Image();

        img.src = e;

        if(img.complete) {

            imgs[i] = img;

            len--;

            if(len == 0) {

                def.resolve();

            }

        }

        else {

            img.onload = (function(j) {

                return function() {

                    imgs[j] = img

                    len--;

                    if(len == 0) {

                        def.resolve();

                    }

                };

            })(i);

            img.onerror = function() {

                len--;

                console.log('fail to load image');

            };

        }

    });

    return def.promise();

}

var list = [......],    //此处省略一万个字符

    imgs = [];

$.when(preloadImg(list, imgs)).done(

    function() {

        //预加载结束

        //do something here

    }

);