js图片预加载示例_基础知识

function loadImage(url, callback) {
if(url!='null') {
var img = new Image();
img.src = url;
if(img.complete) {
callback(img);
} else {
img.onload = function(){
img.onload = null;
callback(img);
}
}
}
}

loadImage(pic_url,loadImage);