JavaScript设计模式(二十七)【数据访问对象模式】

￡神魔★判官ぃ 2021-07-04 20:15 308阅读 0赞

/* 数据访问对象模式： 抽象和封装对数据源的访问与存储，DAO通过对数据源链接的管理方便对数据的访问与存储。 */
    
    var BaseLocalStorage = function(preId, timeSign) { 
        //定义本地存储数据库前缀
        this.preId = preId;
        //定义时间戳与存储数据之间的拼接符
        this.timeSign = timeSign || '|-|';
    }
    
    BaseLocalStorage.prototype = { 
        //操作状态
        status: { 
            SUCCESS: 0,
            FAILURE: 1,
            OVERFLOW: 2,
            TIMEOUT: 2
        },
        storage: localStorage || window.localStorage,
        //获取本地存储数据库数据真实字段
        getKey: function(key) { 
            return this.preId + key;
        },
        //添加（修改）数据
        set: function(key, value, callback, time) { 
            var status = this.status.SUCCESS,
                key = this.getKey(key);
            try { 
                time = new Date(time).getTime() || time.getTime();
            } catch (e) { 
                time = new Date().getTime() + 1000 * 60 * 60 * 24 * 31;
            }
            try { 
                this.storage.setItem(key, time + this.timeSign + value);
            } catch (e) { 
                status = this.status.OVERFLOW;
            }
            callback && callback.call(this, status, key, value);
        },
        get: function(key, callback) { 
            var status = this.status.SUCCESS,
                key = this.getKey(key),
                value = null,
                //时间戳与存储数据之间的拼接符长度
                timeSignLen = this.timeSign.length,
                that = this,
                index,
                time,
                result;
            try { 
                value = that.storage.getItem(key);
            } catch (e) { 
                result = { 
                    status: that.status.FAILURE,
                    value: null
                }
                callback && callback.call(this, result.status, result.value);
            }
            if (value) { 
                index = value.indexOf(that.timeSign);
                time = +value.slice(0, index);
                //如果时间过期
                if (new Date(time).getTime() > new Date().getTime() || time == 0) { 
                    value = value.slice(index + timeSignLen);
                } else { 
                    value = null;
                    status = that.status.TIMEOUT;
                    that.remove(key);
                }
            } else { 
                status = that.status.FAILURE;
            }
            result = { 
                status: status,
                value: value
            }
            callback && callback.call(this, result.status, result.value);
            return result;
        },
        remove: function(key, callback) { 
            var status = this.status.FAILURE,
                key = this.getKey(key),
                value = null;
            try { 
                value = this.storage.getItem(key);
            } catch (e) { 
            }
            if (value) { 
                try { 
                    this.storage.removeItem(key);
                    status = this.status.SUCCESS;
                } catch (e) { 
                }
            }
            callback &&
                callback.call(this,
                    status,
                    status > 0 ? null : value.slice(value.indexOf(this.timeSign) + this.timeSign.length));
        }
    }
    
    
    var ls = new BaseLocalStorage('LS_');
    ls.set('a', 'xiao ming', function() {  console.log(arguments) });
    ls.get('a', function() {  console.log(arguments) })