javascript数据缓存策略之本地存储

db = function() {
var store = window.localStorage, doc = document.documentElement;
if (!store) {
doc.style.behavior = 'url(#default#userData)';
}
return {
/**
* 保存数据
*/
set : function(key, val, context) {
if (store) {
return store.setItem(key, val, context);
} else {
doc.setAttribute(key, value);
return doc.save(context || 'default');
}
},
/**
* 读取数据
*/
get : function(key, context) {
if (store) {
return store.getItem(key, context);
} else {
doc.load(context || 'default');
return doc.getAttribute(key) || '';
}
},
/**
* 删除数据
* @param {Object}
* @param {Object}
*/
rm : function(key, context) {
if (store) {
return store.removeItem(key, context);
} else {
context = context || 'default';
doc.load(context);
doc.removeAttribute(key);
return doc.save(context);
}
},
/**
* 清空数据
*/
clear : function() {
if (store) {
return store.clear();
} else {
doc.expires = -1;
}
}
};
}();

if ( typeof window.XMLHttpRequest === "undefined") {
window.XMLHttpRequest = function() {
return new window.ActiveXObject(navigator.userAgent.indexOf("MSIE 5") >= 0 ? "Microsoft.XMLHTTP" : "Msxml2.XMLHTTP");
};
}
ajax = function(uri, options) {
var httpRequest, httpSuccess, timeout, isTimeout = false, isComplete = false, noop = function() {
};

options = {
method : options.method || "GET",
data : options.data || null,
arguments : options.arguments || null,

onSuccess : options.onSuccess || noop,
onError : options.onError || noop,
onComplete : options.onComplete || noop,
onTimeout : options.onTimeout || noop,
isAsync : options.isAsync || true,
timeout : options.timeout ? options.timeout : 30000,
contentType : options.contentType ? options.contentType : "utf-8",
type : options.type || "xml"
};
uri = uri || "";
timeout = options.timeout;

httpRequest = new window.XMLHttpRequest();
httpRequest.open(options.method, uri, options.isAsync);
//设置编码集
httpRequest.setRequestHeader("Content-Type", options.contentType);

/**
* @ignore
*/
httpSuccess = function(r) {
try {
return (!r.status && location.protocol == "file:") || (r.status >= 200 && r.status < 300) || (r.status == 304) || (navigator.userAgent.indexOf("Safari") > -1 && typeof r.status == "undefined");
} catch(e) {
}
return false;
}
/**
* @ignore
*/
httpRequest.onreadystatechange = function() {
if (httpRequest.readyState == 4) {
if (!isTimeout) {
var o = {};
o.responseText = httpRequest.responseText;
o.responseXML = httpRequest.responseXML;
o.data = options.data;
o.status = httpRequest.status;
o.uri = uri;
o.arguments = options.arguments;

if (httpSuccess(httpRequest)) {
if (options.type === "script") {
eval.call(window, data);
}
options.onSuccess(o);

} else {
options.onError(o);
}
options.onComplete(o);
}
isComplete = true;
//删除对象,防止内存溢出
httpRequest = null;
}
};

httpRequest.send(options.data);

window.setTimeout(function() {
var o;
if (!isComplete) {
isTimeout = true;
o = {};
o.uri = uri;
o.arguments = options.arguments;
options.onTimeout(o);
options.onComplete(o);
}
}, timeout);

return httpRequest;
};

var cacheData = {};
cache = function(url, func, cacheTime) {
//先读内存
if(cacheData[url]){
func.call(this, cacheData[url]);
return;
}else{
var me = this,
chData = db.get(url),
chTime = db.get(url + "__time"),
now = new Date().getTime(),
cacheTime = cacheTime || 60,
ct = now - 60000 * cacheTime, //默认缓存时间为1个小时
success = function(data) {
var res = data.responseText;
cacheData[url] = res;
db.set(url, res);
db.set(url + "__time", now);
func.call(me, res);
};
//存在数据的情况
if (chData && chTime) {
//未过期的情况
if (ct < chTime) {
func.call(this, chData);
} else {//过期的情况
ajax(url, {'onSuccess' : success});
}
} else {
ajax(url, {'onSuccess' : success});
}
}

}