存储在localStorage(作为HTML5中DOM存储的一部分)中的数据可用多长时间?我可以为本地存储的数据设置过期时间吗?
当前回答
// Functions
function removeHtmlStorage(name) {
localStorage.removeItem(name);
localStorage.removeItem(name+'_time');
}
function setHtmlStorage(name, value, expires) {
if (expires==undefined || expires=='null') { var expires = 3600; } // default: 1h
var date = new Date();
var schedule = Math.round((date.setSeconds(date.getSeconds()+expires))/1000);
localStorage.setItem(name, value);
localStorage.setItem(name+'_time', schedule);
}
function statusHtmlStorage(name) {
var date = new Date();
var current = Math.round(+date/1000);
// Get Schedule
var stored_time = localStorage.getItem(name+'_time');
if (stored_time==undefined || stored_time=='null') { var stored_time = 0; }
// Expired
if (stored_time < current) {
// Remove
removeHtmlStorage(name);
return 0;
} else {
return 1;
}
}
// Status
var cache_status = statusHtmlStorage('cache_name');
// Has Data
if (cache_status == 1) {
// Get Cache
var data = localStorage.getItem('cache_name');
alert(data);
// Expired or Empty Cache
} else {
// Get Data
var data = 'Pay in cash :)';
alert(data);
// Set Cache (30 seconds)
if (cache) { setHtmlStorage('cache_name', data, 30); }
}
其他回答
function setStorage(name,value){
return localStorage.setItem(name,JSON.stringify({value:value,timestamp:Math.round((new Date()).getTime()/1000)}));
}
function getStorage(name,timeout){
var object = JSON.parse(localStorage.getItem(name));
if(object){
if(Math.round((new Date()).getTime()/1000) < (object.timestamp+timeout)){
return object.value;
}else{
localStorage.removeItem(name);
}
}
return false;
}
这里强烈推荐使用sessionStorage
它与localStorage相同,但在会话销毁/浏览器关闭时销毁 此外,localStorage可以在选项卡之间共享,而sessionStorage只能在当前选项卡中使用,但值不会在刷新页面或更改页面时改变 sessionStorage对于减少cookie的网络流量也很有用
用于设置值使用
sessionStorage.setItem("key","my value");
获取值使用
var value = sessionStorage.getItem("key");
点击这里查看API
集合的所有方式都是
sessionStorage.key = "my val";
sessionStorage["key"] = "my val";
sessionStorage.setItem("key","my value");
所有得到的方法都是
var value = sessionStorage.key;
var value = sessionStorage["key"];
var value = sessionStorage.getItem("key");
使用angular和local饲草的解决方案:
angular.module('app').service('cacheService', function() {
return {
set: function(key, value, expireTimeInSeconds) {
return localforage.setItem(key, {
data: value,
timestamp: new Date().getTime(),
expireTimeInMilliseconds: expireTimeInSeconds * 1000
})
},
get: function(key) {
return localforage.getItem(key).then(function(item) {
if(!item || new Date().getTime() > (item.timestamp + item.expireTimeInMilliseconds)) {
return null
} else {
return item.data
}
})
}
}
})
Brynner Ferreira提出了一个很好的观点:在过期信息所在的地方存储一个兄弟密钥。这样,如果你有大量的键,或者你的值是大型Json对象,你不需要解析它们来访问时间戳。
以下是一个改进版本:
/* removeStorage: removes a key from localStorage and its sibling expiracy key
params:
key <string> : localStorage key to remove
returns:
<boolean> : telling if operation succeeded
*/
function removeStorage(name) {
try {
localStorage.removeItem(name);
localStorage.removeItem(name + '_expiresIn');
} catch(e) {
console.log('removeStorage: Error removing key ['+ key + '] from localStorage: ' + JSON.stringify(e) );
return false;
}
return true;
}
/* getStorage: retrieves a key from localStorage previously set with setStorage().
params:
key <string> : localStorage key
returns:
<string> : value of localStorage key
null : in case of expired key or failure
*/
function getStorage(key) {
var now = Date.now(); //epoch time, lets deal only with integer
// set expiration for storage
var expiresIn = localStorage.getItem(key+'_expiresIn');
if (expiresIn===undefined || expiresIn===null) { expiresIn = 0; }
if (expiresIn < now) {// Expired
removeStorage(key);
return null;
} else {
try {
var value = localStorage.getItem(key);
return value;
} catch(e) {
console.log('getStorage: Error reading key ['+ key + '] from localStorage: ' + JSON.stringify(e) );
return null;
}
}
}
/* setStorage: writes a key into localStorage setting a expire time
params:
key <string> : localStorage key
value <string> : localStorage value
expires <number> : number of seconds from now to expire the key
returns:
<boolean> : telling if operation succeeded
*/
function setStorage(key, value, expires) {
if (expires===undefined || expires===null) {
expires = (24*60*60); // default: seconds for 1 day
} else {
expires = Math.abs(expires); //make sure it's positive
}
var now = Date.now(); //millisecs since epoch time, lets deal only with integer
var schedule = now + expires*1000;
try {
localStorage.setItem(key, value);
localStorage.setItem(key + '_expiresIn', schedule);
} catch(e) {
console.log('setStorage: Error setting key ['+ key + '] in localStorage: ' + JSON.stringify(e) );
return false;
}
return true;
}
来自W3C草案:
只有出于安全原因或用户请求时,用户代理才应该使本地存储区域的数据过期。用户代理应始终避免在可能访问该数据的脚本运行时删除数据。
你会想要使用setItem(键,值)对你的时间表进行更新;这将使用新数据添加或更新给定的键。
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