Web移动端使用localStorage缓存Js和CSS文件

Posted 2020-09-07

将js css文件缓存到localstorage区可以减少页面在加载时与HTTP请求的交互次数,从而优化页面的加载时间.

电脑端使用localstorage是测试没有问题的,但是用android的apk打包之后,导致localstorage失效,无法进行缓存,查阅资料之后,得知解决方法:

安卓代码:

mWebView.getSettings().setDomStorageEnabled(true);   
mWebView.getSettings().setAppCacheMaxSize(1024*1024*8);  
String appCachePath = getApplicationContext().getCacheDir().getAbsolutePath();  
mWebView.getSettings().setAppCachePath(appCachePath);  
mWebView.getSettings().setAllowFileAccess(true);  

mWebView.getSettings().setAppCacheEnabled(true); 

之后便可以使用localstorage进行缓存,

缓存方法已经封装成了通用的插件:

具体代码如下(网上查询所得):

/**
 * 插件功能:使用localStorage缓存js和css文件,减少http请求和页面渲染的时间,使用于web移动端H5页面的制作
 * 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,当需要更新客户资源时,修改变量值即可
 *         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加载的回调函数参数传入,如:
 *           whir.res.loadJs ("jquery","<%= BasePath %>TurnTable/Script/jquery.min.js",
 *                             function () {
 *                                 whir.res.loadJs(name,url,null)
 *                             });
 */
var whir = window.whir || {};
whir.res = {
    pageVersion : "",//版本,有页面输入,用语刷新localStorage缓存
    loadJs : function (name, url, callback) {//动态加载js文件并缓存
        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();
                            }
                        }
                    }
                }
            } 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.XNLHTTP");
                } 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里的图片路径需要单独处理
                            whir.res.writeCss(css);
                        }
                    }
                }
            } else {
                css = css.replace(/images\//g,"style/images/");//css里的图片路径需要单独处理
                whir.res.writeCss(css);
            }
        } else {
            whir.res.linkCss(url);
        }
    },
    writeJs : function (text) {//往页面写入js\脚本
        var head = document.getElementsByTagName(‘HEAD‘).item(0);//获取head
        var link = document.createElement("script");
        link.type = "text/javascript";
        link.innerhtml = text;
        head.appendChild(link);
    },
    writeCss : function (text) {//往页面写入css样式
        var head = document.getElementsByTagName("HEAD").item(0);
        var link = document.createElement("style");
        link.type = "text/css";
        link.innerHTML = text;
        head.appendChild(link);
    },
    linkJs : function (url) {//往页面引入js
        var head = document.getElementsByTagName(‘HEAD‘).item(0);//获取head
        var link = documenr.createElement("script");
        link.type = "text/javascript";
        link.src = url;
        head.appendChild(link);
    },
    linkCss : function (url) {//往页面引入css
        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);
    }
};

第一次加载时可能会慢,第二次就能明显提升访问速度...