(十一)数据访问对象模式

• 数据访问对象模式：抽象和封装一个对象，对数据源进行访问和存储，这样可以方便对数据的管理，以及避免数据之间的重复，覆盖等问题

/*
   {
     nameSpace|key: expire|value
   }
 */
var DataVisitor = function (nameSpace, splitSign) {
  this.nameSpace = nameSpace;
  this.splitSign = splitSign || '|';
}
DataVisitor.prototype = {
  status: {
    SUCCESS: 0,
    FAILURE: 1,
    OVERFLOW: 2,
    TIMEOUT: 3
  },
  getKey: function (key) {
    return this.nameSpace + this.splitSign + key;
  },
  set: function (key, value, callback, expireTime) {
    var status = this.status.SUCCESS;
    key = this.getKey(key);
    expireTime = expireTime ? expireTime + new Date().getDate() : -1;
    try {
      window.localStorage.setItem(key, expireTime + this.splitSign + value);
    } catch (error) {
      status = this.status.OVERFLOW;
    }
    callback && callback.call(this, status, key, value);
    return value;
  },
  get: function (key, callback) {
    key = this.getKey(key);
    var status = this.status.SUCCESS;
    var value = window.localStorage.getItem(key);
    if (value) {
      var index = value.indexOf(this.splitSign);
      var time = value.slice(0, index);
      if (time > new Date().getTime() || time === '-1') {
        value = value.slice(index + this.splitSign.length);
      } else {
        value = null;
        status = this.status.TIMEOUT;
        window.localStorage.removeItem(key);
      }
    } else {
      status = this.status.FAILURE;
    }
    callback && callback.call(this, status, key, value);
    return value;
  },
  remove: function (key, callback) {
    var status = this.status.FAILURE;
    key = this.getKey(key);
    value = window.localStorage.getItem(key);
    if (value) {
      value = value.slice(value.indexOf(this.splitSign) + this.splitSign.length);
      window.localStorage.removeItem(key);
      status = this.status.SUCCESS;
    }
    callback && callback.call(this, status, key, value);
  }
}
var learnInPro = new DataVisitor('learnInpro');
// 操作一
learnInPro.set('aaa', '123', function (status, key, value) {
  console.log(status, key, value);
});
learnInPro.get('aaa', function(status, key, value) {
  console.log(status, key, value);
})
learnInPro.remove('aaa', function(status, key, value) {
  console.log(status, key, value);
});
// 操作二
learnInPro.set('bbb', '456', function (status, key, value) {
  console.log(status, key, value);
}, 1000 * 2);
learnInPro.get('bbb', function (status, key, value) {
  console.log(status, key, value);
});
setTimeout(function () {
  learnInPro.get('bbb', function (status, key, value) {
    console.log(status, key, value);
  })
}, 1000 * 3);