session不失效，只要浏览器不关闭

简单实现了只要浏览器不关闭，session就不会失效的功能

 

1.javascript定时器定期ajax请求后台

2.避免用户因开多table导致频繁访问后台，利用cookie处理一下

 

function createXHR() {
	var xhr;
	if (window.XMLHttpRequest) {// code for IE7+, Firefox, Chrome, Opera, Safari
		xhr=new XMLHttpRequest();
	} else {// code for IE6, IE5
		xhr=new ActiveXObject("Microsoft.XMLHTTP");
	}
	return xhr;
}
function getCookie(cookieName) {
	if(document.cookie.length > 0) {
		var startIndex = document.cookie.indexOf(cookieName + '=');
		if(startIndex != -1) {		//找到cookie了
			startIndex = startIndex + cookieName.length + 1;
			var endIndex = document.cookie.indexOf(';', startIndex);
			if(endIndex = -1) {		//当前cookie为最后一个，没有';'
				endIndex = document.cookie.length;
			}
			var cookieValue = escape(document.cookie.substring(startIndex, endIndex));
			return cookieValue;
		}
		return null;
	}
	return null;
};
var MINUTES = 10;	//默认10分钟请求一次
function keepSession() {
	if(false) {		//用户没有登录直接返回
		return;
	}
	var LAST_REQUEST_TIME = 'last_equest_time';
	var lastRequestTime = new Date().getTime();
	var cookieValue = getCookie(LAST_REQUEST_TIME);
	if(!cookieValue) {	//第一次登录，还没有cookie
		document.cookie = LAST_REQUEST_TIME + '=' + lastRequestTime;
	} else {
		var intervalTime = lastRequestTime - parseInt(cookieValue);
		if(intervalTime >= 1000*60*MINUTES) {		//只要间隔大于等于规定时间才请求后台
			var xhr = createXHR();
			xhr.open('POST', 'url', true);
			xhr.send(null);
			// 更新cookie
			document.cookie = LAST_REQUEST_TIME + '=' + lastRequestTime;
		}
	}
};
setInterval(keepSession, 1000*60*MINUTES);