将jquery和公共样式缓存到localStorage，可以减少Http请求，从而优化页面加载时间

以下代码：

//入口函数
if (window.localStorage) {
initJs();
initCss("css", "/gfdzp201508257998/Turntable/Style/css_whir.css");
} else {
addFile("/gfdzp201508257998/Turntable/Script/jquery-1.8.3.min.js", "js");
addFile("/gfdzp201508257998/Turntable/Script/whir.turntable.js", "js");
addFile("/gfdzp201508257998/Turntable/Style/css_whir.css", "css");
}

　　

/第一步：加载页面js：先加载jQuery后加载用户脚本
function initJs() {
var name = "jquery";
var url = "/gfdzp201508257998/Turntable/Script/jquery-1.8.3.min.js";
var xhr;
var js = window.localStorage ? localStorage.getItem(name) : "";
if (js == null || js.length == 0) {
if (window.ActiveXObject) {
xhr = new ActiveXObject("Microsoft.XMLHTTP");
} else if (window.XMLHttpRequest) {
xhr = new XMLHttpRequest();
}
xhr.open("GET", url);
xhr.send(null);
xhr.onreadystatechange = function () {
if (xhr.readyState == 4 && xhr.status == 200) {
js = xhr.responseText;
localStorage.setItem(name, js);
js = js == null ? "" : js;
addTxt(js, "js");
initTurntable(); //确保先引用Jquery
}
};
} else {
addTxt(js, "js");
initTurntable();
}
}

　　

//加载自定义脚本
function initTurntable() {
var name = "turntable";
var url = "/gfdzp201508257998/Turntable/Script/whir.turntable.js";
var xhr;
var js = window.localStorage ? localStorage.getItem(name) : "";
if (js == null || js.length == 0) {
if (window.ActiveXObject) {
xhr = new ActiveXObject("Microsoft.XMLHTTP");
} else if (window.XMLHttpRequest) {
xhr = new XMLHttpRequest();
}
xhr.open("GET", url);
xhr.send(null);
xhr.onreadystatechange = function () {
if (xhr.readyState == 4 && xhr.status == 200) {
js = xhr.responseText;
localStorage.setItem(name, js);
js = js == null ? "" : js;
addTxt(js, "js");
}
};
} else {
addTxt(js, "js");
}
}

　　

//第二步：初始化Css
function initCss(name, url) {
var xhr;
var css = window.localStorage ? localStorage.getItem(name) : "";
if (css == null || css.length == 0) {
if (window.ActiveXObject) {
xhr = new ActiveXObject("Microsoft.XMLHTTP");
} else if (window.XMLHttpRequest) {
xhr = new XMLHttpRequest();
}
xhr.open("GET", url);
xhr.send(null);
xhr.onreadystatechange = function () {
if (xhr.readyState == 4 && xhr.status == 200) {
css = xhr.responseText;
localStorage.setItem(name, css);
css = css == null ? "" : css;
css = css.replace(/images\//g, "style/images/");
addTxt(css, "css");
}
};
} else {
css = css.replace(/images\//g, "style/images/");
addTxt(css, "css");
}
}

　　

//辅助方法2：动态添加js，css文件内容
function addTxt(text, fileType) {
var head = document.getElementsByTagName(‘HEAD’).item(0);
var link;
if (fileType == "js") {
link = document.createElement("script");
link.type = "text/javascript";
link.innerHTML = text;
} else {
link = document.createElement("style");
link.type = "text/css";
link.innerHTML = text;
}
head.appendChild(link);
}

　　

封装成JS插件：

[js]
/**
* 插件功能：使用localStorage缓存js和css文件，减少http请求和页面渲染时间，适用于Web移动端H5页面制作。
* 插件作者：zhangqs008@163.com
* 使用方法：
* 1.使用此插件前，需要给插件的pageVersion变量赋值，建议变量值由服务器后端输出，当需要更新客户端资源时，修改版本值即可。
* 2.加载Js：由于js加载有顺序要求，所以需要将后加载的脚本作为前一个脚本的回调参数传入，如：
* whir.res.loadJs("jquery", "<%= BasePath %>Turntable/Script/jquery-1.8.3.min.js",
* function () {
* whir.res.loadJs("turntable", "Script/whir.turntable.js", null);
* });
* 3.加载css，如：whir.res.loadCss("css", "/Style/css_whir.css", null);
*/
var whir = window.whir || {};
whir.res = {
pageVersion: "", //页面版本，由页面输出，用于刷新localStorage缓存
//动态加载js文件并缓存
loadJs: function (name, url, callback) {
if (window.localStorage) {
var xhr;
var js = localStorage.getItem(name);
if (js == null || js.length == 0 || this.pageVersion != localStorage.getItem("version")) {
if (window.ActiveXObject) {
xhr = new ActiveXObject("Microsoft.XMLHTTP");
} else if (window.XMLHttpRequest) {
xhr = new XMLHttpRequest();
}
if (xhr != null) {
xhr.open("GET", url);
xhr.send(null);
xhr.onreadystatechange = function () {
if (xhr.readyState == 4 && xhr.status == 200) {
js = xhr.responseText;
localStorage.setItem(name, js);
localStorage.setItem("version", whir.res.pageVersion);
js = js == null ? "" : js;
whir.res.writeJs(js);
if (callback != null) {
callback(); //回调，执行下一个引用
}
}
};
}
} else {
whir.res.writeJs(js);
if (callback != null) {
callback(); //回调，执行下一个引用
}
}
} else {
whir.res.linkJs(url);
}
},
loadCss: function (name, url) {
if (window.localStorage) {
var xhr;
var css = localStorage.getItem(name);
if (css == null || css.length == 0 || this.pageVersion != localStorage.getItem("version")) {
if (window.ActiveXObject) {
xhr = new ActiveXObject("Microsoft.XMLHTTP");
} else if (window.XMLHttpRequest) {
xhr = new XMLHttpRequest();
}
if (xhr != null) {
xhr.open("GET", url);
xhr.send(null);
xhr.onreadystatechange = function () {
if (xhr.readyState == 4 && xhr.status == 200) {
css = xhr.responseText;
localStorage.setItem(name, css);
localStorage.setItem("version", whir.res.pageVersion);
css = css == null ? "" : css;
css = css.replace(/images\//g, "style/images/"); //css里的图片路径需单独处理
whir.res.writeCss(css);
}
};
}
} else {
css = css.replace(/images\//g, "style/images/"); //css里的图片路径需单独处理
whir.res.writeCss(css);
}
} else {
whir.res.linkCss(url);
}
},
//往页面写入js脚本
writeJs: function (text) {
var head = document.getElementsByTagName(‘HEAD’).item(0);
var link = document.createElement("script");
link.type = "text/javascript";
link.innerHTML = text;
head.appendChild(link);
},
//往页面写入css样式
writeCss: function (text) {
var head = document.getElementsByTagName(‘HEAD’).item(0);
var link = document.createElement("style");
link.type = "text/css";
link.innerHTML = text;
head.appendChild(link);
},
//往页面引入js脚本
linkJs: function (url) {
var head = document.getElementsByTagName(‘HEAD’).item(0);
var link = document.createElement("script");
link.type = "text/javascript";
link.src = url;
head.appendChild(link);
},
//往页面引入css样式
linkCss: function (url) {
var head = document.getElementsByTagName(‘HEAD’).item(0);
var link = document.createElement("link");
link.type = "text/css";
link.rel = "stylesheet";
link.rev = "stylesheet";
link.media = "screen";
link.href = url;
head.appendChild(link);
}
}
[/js]

调用该插件：

[js]
<script type="text/javascript">
//入口函数
whir.res.pageVersion = "1002"; //页面版本，用于检测是否需要更新缓存
whir.res.loadJs("jquery", "/gfdzp201508257998/Turntable/Script/jquery-1.8.3.min.js",
function () {
whir.res.loadJs("turntable", "/gfdzp201508257998/Turntable/Script/whir.turntable.js", null);
});
whir.res.loadCss("css", "/gfdzp201508257998/Turntable/Style/css_whir.css", null);
</script>
[/js]