利用本地存储，保存js文件

var ScriptStorage = function (url) {
    this.url = url;
    this.storageName = 'script-' + url.split('?')[0];
    this.init();
}

ScriptStorage.prototype = {
    init: function () {
        if(this.hasStorage){
            var storage = this.storage.get(this.storageName);
            if(storage && storage.url === this.url){
                this.scriptHandle(storage.script, 0);
            }else{
                this.xhr(this.url, this.scriptHandle.bind(this));
            }
        }else{
            var script = this.createElement('script',{"src": this.url});
            document.body.appendChild(script);
        }
    },
    hasStorage: (function(){
        var test = 'test';
        try {
            localStorage.setItem(test, test);
            localStorage.removeItem(test);
            return true;
        } catch(e) {
            return false;
        }
    }()),
    scriptHandle: function (data, restorage) {
        if(data){
            var script = this.createElement('script');
            script.innerHTML = data;
            document.body.appendChild(script);
            var storageData = {
                url: this.url,
                script: data
            }
            if(restorage){
                this.storage.set(this.storageName, storageData);
            }
        }
    },
    createElement: function (tag, option) {
        var el = document.createElement(tag);
        for (var i in option) {
            if(option.hasOwnProperty(i)){
                el.setAttribute(i, option[i]);
            }
        }
        return el;
    },
    storage: {
        get: function (key) {
            return JSON.parse(window.localStorage.getItem(key));
        },
        set: function (key, value) {
            return window.localStorage.setItem(key, JSON.stringify(value));
        }
    },
    xhr: function (url, callback) {
        var xhr = new XMLHttpRequest();
        xhr.onreadystatechange = function() {
            if (xhr.readyState == 4 && xhr.status ==200) {
                callback(xhr.responseText, !0);
            }
        }
        xhr.open('GET', url, true);
        xhr.send(null);
    }
}

var scriptUrl = 'test.js?version=1.0.0';

var storageScript = new ScriptStorage(scriptUrl);