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  • HTML5本地存储Localstorage

    什么是localstorage

      前几天在老项目中发现有对cookie的操作觉得很奇怪,咨询下来是要缓存一些信息,以避免在URL上面传递参数,但没有考虑过cookie会带来什么问题:

      ① cookie大小限制在4k左右,不适合存业务数据
      ② cookie每次随HTTP事务一起发送,浪费带宽

      我们是做移动项目的,所以这里真实适合使用的技术是localstorage,localstorage可以说是对cookie的优化,使用它可以方便在客户端存储数据,并且不会随着HTTP传输,但也不是没有问题:

      ① localstorage大小限制在500万字符左右,各个浏览器不一致
      ② localstorage在隐私模式下不可读取
      ③ localstorage本质是在读写文件,数据多的话会比较卡(firefox会一次性将数据导入内存,想想就觉得吓人啊)
      ④ localstorage不能被爬虫爬取,不要用它完全取代URL传参

      瑕不掩瑜,以上问题皆可避免,所以我们的关注点应该放在如何使用localstorage上,并且是如何正确使用。

     localstorage的使用

      基础知识

      localstorage存储对象分为两种:

      ① sessionStrage: session即会话的意思,在这里的session是指用户浏览某个网站时,从进入网站到关闭网站这个时间段,session对象的有效期就只有这么长。

      ② localStorage: 将数据保存在客户端硬件设备上,不管它是什么,意思就是下次打开计算机时候数据还在。

      两者区别就是一个作为临时保存,一个长期保存。

      这里来一段简单的代码说明其基本使用:

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    <div id="msg" <span id="15_nwp" style=" auto; height: auto; float: none;"><a id="15_nwl" href="http://cpro.baidu.com/cpro/ui/uijs.php?app_id=0&c=news&cf=1001&ch=0&di=128&fv=17&is_app=0&jk=69eb6b88bc58f1e3&k=style&k0=style&kdi0=0&luki=3&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_id=1&sid=e3f158bc886beb69&ssp2=1&stid=0&t=tpclicked3_hc&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6283%2Ehtml&urlid=0" target="_blank" mpid="15" style="text-decoration: none;"><span style="color:#0000ff;font-size:14px;auto;height:auto;float:none;">style</span></a></span>="margin: 10px 0; border: 1px solid black; padding: 10px; 300px;
      height: 100px;">
    </div>
    <input type="text" id="text" />
    <select id="type">
      <option value="session">sessionStorage</option>
      <option value="local">localStorage</option>
    </select>
    <button onclick="save();">
      保存数据</button>
    <button onclick="load();">
      读取数据</button>
    <script type="text/<span id="16_nwp" style=" auto; height: auto; float: none;"><a id="16_nwl" href="http://cpro.baidu.com/cpro/ui/uijs.php?app_id=0&c=news&cf=1001&ch=0&di=128&fv=17&is_app=0&jk=69eb6b88bc58f1e3&k=javascript&k0=javascript&kdi0=0&luki=8&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_id=1&sid=e3f158bc886beb69&ssp2=1&stid=0&t=tpclicked3_hc&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6283%2Ehtml&urlid=0" target="_blank" mpid="16" style="text-decoration: none;"><span style="color:#0000ff;font-size:14px;auto;height:auto;float:none;">javascript</span></a></span>">
      var msg = document.getElementById('msg'),
                text = document.getElementById('text'),
                type = document.getElementById('type');
     
      function save() {
        var str = text.value;
        var t = type.value;
        if (t == 'session') {
          sessionStorage.setItem('msg', str);
        } else {
          localStorage.setItem('msg', str);
        }
      }
     
      function load() {
        var t = type.value;
        if (t == 'session') {
          msg.innerHTML = sessionStorage.getItem('msg');
        } else {
          msg.innerHTML = localStorage.getItem('msg');
        }
      }
    </script>

     真实场景

      实际工作中对localstorage的使用一般有以下需求:

      ① 缓存一般信息,如搜索页的出发城市,达到城市,非实时定位信息

      ② 缓存城市列表数据,这个数据往往比较大

      ③ 每条缓存信息需要可追踪,比如服务器通知城市数据更新,这个时候在最近一次访问的时候要自动设置过期

      ④ 每条信息具有过期日期状态,在过期外时间需要由服务器拉取数据

      ⑤ ......

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    define([], function () {
     
      var Storage = _.inherit({
        //默认属性
        propertys: function () {
     
          //<span id="4_nwp" style=" auto; height: auto; float: none;"><a id="4_nwl" href="http://cpro.baidu.com/cpro/ui/uijs.php?app_id=0&c=news&cf=1001&ch=0&di=128&fv=17&is_app=0&jk=69eb6b88bc58f1e3&k=%B4%FA%C0%ED&k0=%B4%FA%C0%ED&kdi0=0&luki=1&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_id=1&sid=e3f158bc886beb69&ssp2=1&stid=0&t=tpclicked3_hc&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6283%2Ehtml&urlid=0" target="_blank" mpid="4" style="text-decoration: none;"><span style="color:#0000ff;font-size:14px;auto;height:auto;float:none;">代理</span></a></span>对象,默认为localstorage
          this.sProxy = window.localStorage;
     
          //60 * 60 * 24 * 30 * 1000 ms ==30天
          this.defaultLifeTime = 2592000000;
     
          //本地<span id="5_nwp" style=" auto; height: auto; float: none;"><a id="5_nwl" href="http://cpro.baidu.com/cpro/ui/uijs.php?app_id=0&c=news&cf=1001&ch=0&di=128&fv=17&is_app=0&jk=69eb6b88bc58f1e3&k=%BB%BA%B4%E6&k0=%BB%BA%B4%E6&kdi0=0&luki=4&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_id=1&sid=e3f158bc886beb69&ssp2=1&stid=0&t=tpclicked3_hc&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6283%2Ehtml&urlid=0" target="_blank" mpid="5" style="text-decoration: none;"><span style="color:#0000ff;font-size:14px;auto;height:auto;float:none;">缓存</span></a></span>用以存放所有localstorage键值与过期日期的映射
          this.keyCache = 'SYSTEM_KEY_TIMEOUT_MAP';
     
          //当缓存容量已满,每次删除的缓存数
          this.removeNum = 5;
     
        },
     
        assert: function () {
          if (this.sProxy === null) {
            throw 'not override sProxy property';
          }
        },
     
        initialize: function (opts) {
          this.propertys();
          this.assert();
        },
     
        /*
        新增localstorage
        数据格式包括唯一键值,json字符串,过期日期,存入日期
        sign 为格式化后的请求参数,用于同一请求不同参数时候返回新数据,比如列表为北京的城市,后切换为上海,会判断tag不同而更新<span id="6_nwp" style=" auto; height: auto; float: none;"><a id="6_nwl" href="http://cpro.baidu.com/cpro/ui/uijs.php?app_id=0&c=news&cf=1001&ch=0&di=128&fv=17&is_app=0&jk=69eb6b88bc58f1e3&k=%BB%BA%B4%E6&k0=%BB%BA%B4%E6&kdi0=0&luki=4&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_id=1&sid=e3f158bc886beb69&ssp2=1&stid=0&t=tpclicked3_hc&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6283%2Ehtml&urlid=0" target="_blank" mpid="6" style="text-decoration: none;"><span style="color:#0000ff;font-size:14px;auto;height:auto;float:none;">缓存</span></a></span>数据,tag相当于签名
        每一键值只会缓存一条信息
        */
        set: function (key, value, timeout, sign) {
          var _d = new Date();
          //存入日期
          var indate = _d.getTime();
     
          //最终保存的数据
          var entity = null;
     
          if (!timeout) {
            _d.setTime(_d.getTime() + this.defaultLifeTime);
            timeout = _d.getTime();
          }
     
          //
          this.setKeyCache(key, timeout);
          entity = this.buildStorageObj(value, indate, timeout, sign);
     
          try {
            this.sProxy.setItem(key, JSON.stringify(entity));
            return true;
          } catch (e) {
            //localstorage写满时,全清掉
            if (e.name == 'QuotaExceededError') {
              //            this.sProxy.clear();
              //localstorage写满时,选择离过期时间最近的数据删除,这样也会有些影响,但是感觉比全清除好些,如果<span id="7_nwp" style=" auto; height: auto; float: none;"><a id="7_nwl" href="http://cpro.baidu.com/cpro/ui/uijs.php?app_id=0&c=news&cf=1001&ch=0&di=128&fv=17&is_app=0&jk=69eb6b88bc58f1e3&k=%BB%BA%B4%E6&k0=%BB%BA%B4%E6&kdi0=0&luki=4&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_id=1&sid=e3f158bc886beb69&ssp2=1&stid=0&t=tpclicked3_hc&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6283%2Ehtml&urlid=0" target="_blank" mpid="7" style="text-decoration: none;"><span style="color:#0000ff;font-size:14px;auto;height:auto;float:none;">缓存</span></a></span>过多,此过程比较耗时,100ms以内
              if (!this.removeLastCache()) throw '本次<span id="8_nwp" style=" auto; height: auto; float: none;"><a id="8_nwl" href="http://cpro.baidu.com/cpro/ui/uijs.php?app_id=0&c=news&cf=1001&ch=0&di=128&fv=17&is_app=0&jk=69eb6b88bc58f1e3&k=%CA%FD%BE%DD%B4%E6%B4%A2&k0=%CA%FD%BE%DD%B4%E6%B4%A2&kdi0=0&luki=2&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_id=1&sid=e3f158bc886beb69&ssp2=1&stid=0&t=tpclicked3_hc&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6283%2Ehtml&urlid=0" target="_blank" mpid="8" style="text-decoration: none;"><span style="color:#0000ff;font-size:14px;auto;height:auto;float:none;">数据存储</span></a></span>量过大';
              this.set(key, value, timeout, sign);
            }
            console && console.log(e);
          }
          return false;
        },
     
        //删除过期缓存
        removeOverdueCache: function () {
          var tmpObj = null, i, len;
     
          var now = new Date().getTime();
          //取出键值对
          var cacheStr = this.sProxy.getItem(this.keyCache);
          var cacheMap = [];
          var newMap = [];
          if (!cacheStr) {
            return;
          }
     
          cacheMap = JSON.parse(cacheStr);
     
          for (i = 0, len = cacheMap.length; i < len; i++) {
            tmpObj = cacheMap[i];
            if (tmpObj.timeout < now) {
              this.sProxy.removeItem(tmpObj.key);
            } else {
              newMap.push(tmpObj);
            }
          }
          this.sProxy.setItem(this.keyCache, JSON.stringify(newMap));
     
        },
     
        removeLastCache: function () {
          var i, len;
          var num = this.removeNum || 5;
     
          //取出键值对
          var cacheStr = this.sProxy.getItem(this.keyCache);
          var cacheMap = [];
          var delMap = [];
     
          //说明本次存储过大
          if (!cacheStr) return false;
     
          cacheMap.sort(function (a, b) {
            return a.timeout - b.timeout;
          });
     
          //删除了哪些数据
          delMap = cacheMap.splice(0, num);
          for (i = 0, len = delMap.length; i < len; i++) {
            this.sProxy.removeItem(delMap[i].key);
          }
     
          this.sProxy.setItem(this.keyCache, JSON.stringify(cacheMap));
          return true;
        },
     
        setKeyCache: function (key, timeout) {
          if (!key || !timeout || timeout < new Date().getTime()) return;
          var i, len, tmpObj;
     
          //获取当前已经<span id="9_nwp" style=" auto; height: auto; float: none;"><a id="9_nwl" href="http://cpro.baidu.com/cpro/ui/uijs.php?app_id=0&c=news&cf=1001&ch=0&di=128&fv=17&is_app=0&jk=69eb6b88bc58f1e3&k=%BB%BA%B4%E6&k0=%BB%BA%B4%E6&kdi0=0&luki=4&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_id=1&sid=e3f158bc886beb69&ssp2=1&stid=0&t=tpclicked3_hc&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6283%2Ehtml&urlid=0" target="_blank" mpid="9" style="text-decoration: none;"><span style="color:#0000ff;font-size:14px;auto;height:auto;float:none;">缓存</span></a></span>的键值字符串
          var oldstr = this.sProxy.getItem(this.keyCache);
          var oldMap = [];
          //当前key是否已经存在
          var <span id="10_nwp" style=" auto; height: auto; float: none;"><a id="10_nwl" href="http://cpro.baidu.com/cpro/ui/uijs.php?app_id=0&c=news&cf=1001&ch=0&di=128&fv=17&is_app=0&jk=69eb6b88bc58f1e3&k=flag&k0=flag&kdi0=0&luki=9&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_id=1&sid=e3f158bc886beb69&ssp2=1&stid=0&t=tpclicked3_hc&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6283%2Ehtml&urlid=0" target="_blank" mpid="10" style="text-decoration: none;"><span style="color:#0000ff;font-size:14px;auto;height:auto;float:none;">flag</span></a></span> = false;
          var obj = {};
          obj.key = key;
          obj.timeout = timeout;
     
          if (oldstr) {
            oldMap = JSON.parse(oldstr);
            if (!_.isArray(oldMap)) oldMap = [];
          }
     
          for (i = 0, len = oldMap.length; i < len; i++) {
            tmpObj = oldMap[i];
            if (tmpObj.key == key) {
              oldMap[i] = obj;
              flag = true;
              break;
            }
          }
          if (!<span id="11_nwp" style=" auto; height: auto; float: none;"><a id="11_nwl" href="http://cpro.baidu.com/cpro/ui/uijs.php?app_id=0&c=news&cf=1001&ch=0&di=128&fv=17&is_app=0&jk=69eb6b88bc58f1e3&k=flag&k0=flag&kdi0=0&luki=9&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_id=1&sid=e3f158bc886beb69&ssp2=1&stid=0&t=tpclicked3_hc&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6283%2Ehtml&urlid=0" target="_blank" mpid="11" style="text-decoration: none;"><span style="color:#0000ff;font-size:14px;auto;height:auto;float:none;">flag</span></a></span>) oldMap.push(obj);
          //最后将新数组放到<span id="12_nwp" style=" auto; height: auto; float: none;"><a id="12_nwl" href="http://cpro.baidu.com/cpro/ui/uijs.php?app_id=0&c=news&cf=1001&ch=0&di=128&fv=17&is_app=0&jk=69eb6b88bc58f1e3&k=%BB%BA%B4%E6&k0=%BB%BA%B4%E6&kdi0=0&luki=4&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_id=1&sid=e3f158bc886beb69&ssp2=1&stid=0&t=tpclicked3_hc&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6283%2Ehtml&urlid=0" target="_blank" mpid="12" style="text-decoration: none;"><span style="color:#0000ff;font-size:14px;auto;height:auto;float:none;">缓存</span></a></span>中
          this.sProxy.setItem(this.keyCache, JSON.stringify(oldMap));
     
        },
     
        buildStorageObj: function (value, indate, timeout, sign) {
          var obj = {
            value: value,
            timeout: timeout,
            sign: sign,
            indate: indate
          };
          return obj;
        },
     
        get: function (key, sign) {
          var result, now = new Date().getTime();
          try {
            result = this.sProxy.getItem(key);
            if (!result) return null;
            result = JSON.parse(result);
     
            //数据过期
            if (result.timeout < now) return null;
     
            //需要验证签名
            if (sign) {
              if (sign === result.sign)
                return result.value;
              return null;
            } else {
              return result.value;
            }
     
          } catch (e) {
            console && console.log(e);
          }
          return null;
        },
     
        //获取签名
        getSign: function (key) {
          var result, sign = null;
          try {
            result = this.sProxy.getItem(key);
            if (result) {
              result = JSON.parse(result);
              sign = result && result.sign
            }
          } catch (e) {
            console && console.log(e);
          }
          return sign;
        },
     
        remove: function (key) {
          return this.sProxy.removeItem(key);
        },
     
        clear: function () {
          this.sProxy.clear();
        }
      });
     
      Storage.getInstance = function () {
        if (this.instance) {
          return this.instance;
        } else {
          return this.instance = new this();
        }
      };
     
      return Storage;
     
    });

      这段代码包含了localstorage的基本操作,并且对以上问题做了处理,而真实的使用还要再抽象:

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    define(['AbstractStorage'], function (AbstractStorage) {
     
      var Store = _.inherit({
        //默认属性
        propertys: function () {
     
          //每个对象一定要具有存储键,并且不能重复
          this.key = null;
     
          //默认一条数据的生命周期,S为秒,M为分,D为天
          this.lifeTime = '30M';
     
          //默认返回数据
          //      this.defaultData = null;
     
          //<span id="2_nwp" style=" auto; height: auto; float: none;"><a id="2_nwl" href="http://cpro.baidu.com/cpro/ui/uijs.php?app_id=0&c=news&cf=1001&ch=0&di=128&fv=17&is_app=0&jk=69eb6b88bc58f1e3&k=%B4%FA%C0%ED&k0=%B4%FA%C0%ED&kdi0=0&luki=1&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_id=1&sid=e3f158bc886beb69&ssp2=1&stid=0&t=tpclicked3_hc&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6283%2Ehtml&urlid=0" target="_blank" mpid="2" style="text-decoration: none;"><span style="color:#0000ff;font-size:14px;auto;height:auto;float:none;">代理</span></a></span>对象,localstorage对象
          this.sProxy = new AbstractStorage();
     
        },
     
        setOption: function (options) {
          _.extend(this, options);
        },
     
        assert: function () {
          if (this.key === null) {
            throw 'not override key property';
          }
          if (this.sProxy === null) {
            throw 'not override sProxy property';
          }
        },
     
        initialize: function (opts) {
          this.propertys();
          this.setOption(opts);
          this.assert();
        },
     
        _getLifeTime: function () {
          var timeout = 0;
          var str = this.lifeTime;
          var unit = str.charAt(str.length - 1);
          var num = str.substring(0, str.length - 1);
          var Map = {
            D: 86400,
            H: 3600,
            M: 60,
            S: 1
          };
          if (typeof unit == 'string') {
            unit = unit.toUpperCase();
          }
          timeout = num;
          if (unit) timeout = Map[unit];
     
          //单位为毫秒
          return num * timeout * 1000 ;
        },
     
        //<span id="3_nwp" style=" auto; height: auto; float: none;"><a id="3_nwl" href="http://cpro.baidu.com/cpro/ui/uijs.php?app_id=0&c=news&cf=1001&ch=0&di=128&fv=17&is_app=0&jk=69eb6b88bc58f1e3&k=%BB%BA%B4%E6&k0=%BB%BA%B4%E6&kdi0=0&luki=4&n=10&p=baidu&q=06011078_cpr&rb=0&rs=1&seller_id=1&sid=e3f158bc886beb69&ssp2=1&stid=0&t=tpclicked3_hc&tu=u1922429&u=http%3A%2F%2Fwww%2Eadmin10000%2Ecom%2Fdocument%2F6283%2Ehtml&urlid=0" target="_blank" mpid="3" style="text-decoration: none;"><span style="color:#0000ff;font-size:14px;auto;height:auto;float:none;">缓存</span></a></span>数据
        set: function (value, sign) {
          //获取过期时间
          var timeout = new Date();
          timeout.setTime(timeout.getTime() + this._getLifeTime());
          this.sProxy.set(this.key, value, timeout.getTime(), sign);
        },
     
        //设置单个属性
        setAttr: function (name, value, sign) {
          var key, obj;
          if (_.isObject(name)) {
            for (key in name) {
              if (name.hasOwnProperty(key)) this.setAttr(k, name[k], value);
            }
            return;
          }
     
          if (!sign) sign = this.getSign();
     
          //获取当前对象
          obj = this.get(sign) || {};
          if (!obj) return;
          obj[name] = value;
          this.set(obj, sign);
     
        },
     
        getSign: function () {
          return this.sProxy.getSign(this.key);
        },
     
        remove: function () {
          this.sProxy.remove(this.key);
        },
     
        removeAttr: function (attrName) {
          var obj = this.get() || {};
          if (obj[attrName]) {
            delete obj[attrName];
          }
          this.set(obj);
        },
     
        get: function (sign) {
          var result = [], isEmpty = true, a;
          var obj = this.sProxy.get(this.key, sign);
          var type = typeof obj;
          var o = { 'string': true, 'number': true, 'boolean': true };
          if (o[type]) return obj;
     
          if (_.isArray(obj)) {
            for (var i = 0, len = obj.length; i < len; i++) {
              result[i] = obj[i];
            }
          } else if (_.isObject(obj)) {
            result = obj;
          }
     
          for (a in result) {
            isEmpty = false;
            break;
          }
          return !isEmpty ? result : null;
        },
     
        getAttr: function (attrName, tag) {
          var obj = this.get(tag);
          var attrVal = null;
          if (obj) {
            attrVal = obj[attrName];
          }
          return attrVal;
        }
     
      });
     
      Store.getInstance = function () {
        if (this.instance) {
          return this.instance;
        } else {
          return this.instance = new this();
        }
      };
     
      return Store;
    });

      我们真实使用的时候是使用store这个类操作localstorage,代码结束简单测试:

      存储完成,以后都不会走请求,于是今天的代码基本结束 ,最后在android Hybrid中有一后退按钮,此按钮一旦按下会回到上一个页面,这个时候里面的localstorage可能会读取失效!一个简单不靠谱的解决方案是在webapp中加入:

    1
    window.onunload = function () { };//适合单页应用,不要问我为什么,我也不知道

     结语

      localstorage是移动开发必不可少的技术点,需要深入了解,具体业务代码后续会放到git上,有兴趣的朋友可以去了解

    转自:http://www.admin10000.com/document/6283.html

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  • 原文地址:https://www.cnblogs.com/JJ-Chen/p/4516464.html
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