javascript preload&lazy load

代码如下:

(function($) {
(function($) {
$.preload = function(data, cfg) {
return new Loader(data, cfg);
};
var maps = {}, on = $.event.add, un = $.event.remove, head = document.getElementsByTagName('head')[0], body =
document.body, bs = $.browser, ie = bs.msie, webkit = bs.webkit, gecko = bs.mozilla, space = 1000, ajax =
$.ajax,
loaders = $.preload.loaders = {
'js' : function(url, callback, timeout, defer) {
var s, timer;
if (defer) {
if (ie) {
return loaders.img(url, callback, timeout);
} else {
s = document.createElement('object');
s.data = url;
s.width = s.height = 0;
}
} else {
s = document.createElement('script');
s.setAttribute('type', 'text/javascript');
s.setAttribute('src', url);
}
function f() {
if (timer)
clearTimeout(timer);
s.onreadystatechange = s.onload = s.onerror = null;
callback(url, false);
}
if (ie) {
s.onreadystatechange = function() {
if (this.readyState === 'loaded' || this.readyState === 'complete') {
if (timer)
clearTimeout(timer);
s.onreadystatechange = null;
callback(url, true);
}
};
} else {
s.onload = function() {
if (timer)
clearTimeout(timer);
s.onload = s.onerror = null;
callback(url, true);
};
s.onerror = f;
}
timer = setTimeout(f, timeout);
body.appendChild(s);
},
'css' : function(url, callback, timeout, defer) {
if (defer) {
return loaders.js(url, callback, timeout, defer);
}
var s = document.createElement('link'), timer;
s.setAttribute('rel', 'stylesheet');
s.setAttribute('type', 'text/css');
s.setAttribute('href', url);
function f() {
if (timer)
clearTimeout(timer);
s.onreadystatechange = s.onload = s.onerror = null;
callback(url, false);
}
if (ie) {
s.onreadystatechange = function() {
if (this.readyState === 'loaded' || this.readyState === 'complete') {
if (timer)
clearTimeout(timer);
s.onreadystatechange = null;
callback(url, true);
}
};
timer = setTimeout(f, timeout);
} else if (webkit || gecko) {
timer = new Date();
function f() {
if (('sheet' in s) && ('cssRules' in s.sheet)) {
try {
callback(url, !!s.sheet.cssRules[0]);
} catch (e) {
setTimeout(f, space);
}
} else if (new Date() - timer > timeout) {
callback(url, false);
} else {
setTimeout(f, space);
}
}
setTimeout(f, space * 2);
} else {
s.onload = function() {
if (timer)
clearTimeout(timer);
s.onload = s.onerror = null;
callback(url, true);
};
s.onerror = f;
timer = setTimeout(f, timeout);
}
head.appendChild(s);
},
'img' : function(url, callback, timeout) {
var s = new Image(), timer;
function f() {
if (timer)
clearTimeout(timer);
s.onload = s.onerror = null;
callback(url, false);
}
s.onload = function() {
if (timer)
clearTimeout(timer);
s.onload = s.onerror = null;
callback(url, true);
};
s.onerror = f;
timer = setTimeout(f, timeout);
s.src = url;
},
'ajax' : function(url, callback, cfg) {
cfg = cfg || {};
cfg.url = url;
cfg.success = function(data) {
callback(url, true, data);
};
cfg.error = function() {
callback(url, false);
};
ajax(cfg);
}
};
function Loader(data, cfg) {
var self = this, cur = -1, items = [], pendings = [], done, i = 0, l = data.length, j, m, s, t, c, d, tt, item, doing =
0, load;
cfg = cfg || {};
for (; i < l; ++i) {
item = data[i];
if (typeof item === 'string') {
s = item.substr(item.lastIndexOf('.') + 1);
items.push(maps[item] = {
type : loaders[s] ? s : 'img',
url : item
});
} else if (item.urls) {
for (j = 0, s = item.type, t = item.require, c = item.callback, d = item.defer, tt = item.timeout, item =
item.urls, m = item.length; j < m; ++j) {
s = s || item[j].substr(item[j].lastIndexOf('.') + 1);
items.push(maps[item[j]] = {
type : loaders[s] ? s : 'img',
url : item[j],
require : t,
callback : c,
defer : d,
timeout : tt
});
}
} else {
if (!item.type) {
s = item.url.substr(item.url.lastIndexOf('.') + 1);
item.type = loaders[s] ? s : 'img';
}
items.push(maps[item.url] = item);
}
}
this.success = this.fail = this.progress = 0;
if (cfg.onFinish)
this.onFinish = cfg.onFinish;
timeout = cfg.timeout || 2000;
function callback(url, flag, data) {
if (flag) {
++self.success;
} else {
++self.fail;
}
self.progress = (self.success + self.fail) / items.length;
console.info(url);
console.warn(flag);
item = maps[url];
item.success = flag;
if (self.progress === 1) {
self.stop();
}
if (item.parent && !item.defer && !cfg.defer) {
$(item.parent)[0].innerHTML = data || '';
}
if (item.callback) {
item.callback(data);
}
item.done = true;
--doing;
}
function runnable(item, pend) {
var it;
if (typeof item.require === 'string') {
if (item.done)
return false;
if (!item.require)
return true;
it = maps[item.require];
if (!it || it.done) {
if (pend)
pendings.shift();
if (it && it.success) {
return true;
} else {
callback(item.url, false);
}
} else if (!pend) {
pendings.push(item);
}
} else {
for (it = item.length; it--;) {
if (!runnable(item[it], pend))
return false;
}
return true;
}
}
function run() {
var item = pendings[0];
if (!item || !runnable(item, true)) {
while (item = items[++cur]) {
if (runnable(item)) {
break;
}
}
}
if (item) {
var fn = loaders[item.type || 'img'];
if (fn) {
++doing;
if (item.type === 'ajax') {
if (item.cfg && !item.cfg.timeout)
item.cfg.timeout = timeout;
fn(item.url, callback, item.cfg);
} else {
fn(item.url, callback, item.timeout || timeout, item.defer === undefined ? cfg.defer
: item.defer);
}
};
if (load) {
run();
} else {
self.timer = setTimeout(run, space);
}
} else if (pendings.length) {
self.timer = setTimeout(run, space);
}
}
this.start = function(delay) {
if (!done)
this.timer = setTimeout(run, delay > space ? delay : space);
};
this.stop = function() {
if (this.timer) {
clearTimeout(this.timer);
this.timer = null;
done = true;
if (this.onFinish) {
if (!doing)
this.onFinish();
else {
s = setInterval(function() {
if (!doing) {
clearInterval(s);
self.onFinish();
}
}, space);
}
}
}
};
this.pause = function() {
clearTimeout(this.timer);
};
this.resume = function() {
this.timer = setTimeout(run, space);
};
this.load = function() {
clearTimeout(this.timer);
load = true;
run();
};
}
})(jQuery);
/**
* @example
* var loader = $.preload([
// 字符串，采用默认配置
'1.jpg', '1.js',
// 对象，自定义配置，如type, require, timeout, defer, callback
{
type : 'img',
url : 'http://foo.com/foo',
timeout : 10
}, {
url : '3.js',
callback : fn,
defer : true,
require : '1.js'
},
// 对象，可用urls指定一组相同配置
{
type : 'css',
urls : ['4.css', '5.css']
}], {
// 加载结束后调用
onFinish : fn,
// 加载超时
timeout : 50
});
// 开始预加载
loader.start();
loader.stop();
// 暂停预加载
loader.pause();
loader.resume();
// 实时加载
loader.load();
*/