Javascript XMLHttpRequest问题 [英] Javascript XMLHttpRequest issue

问题描述

我使用以下脚本来监视是否可以定期连接到网站（在我的示例代码中为10秒）。我遇到了两个问题，任何想法如何解决它们？

I am using the following script to monitor whether I can connect to a web site in a regular interval (10 seconds in my sample code). I met with two issues, any ideas how to solve them?

1. 如果一个网站非常慢并且10内没有回复秒（使PingWebSite不返回），我发现因为10秒间隔到达而将执行2秒的PingWebSite调用。我的目的是我只想要一次调用PingWebSite正在执行，如果10秒间隔到达并且之前的PingWebSite正在执行，我想阻止当前的PingWebSite执行。任何想法如何解决这个问题？

1. If a web site is very slow and no response within 10 seconds (making PingWebSite not return), I find 2 second call to PingWebSite will be executed because of 10 second interval arrives. My purpose is I want only one call to PingWebSite is under execution, and if 10 seconds interval arrives and previous PingWebSite is executing, I want to prevent current PingWebSite from execution. Any ideas how to solve this?

我发现一个奇怪的问题，当我连接到一个非常慢的网站时，代码路径执行到警告（连接）;，然后我希望异常被抛出超时，但在我的调试中，没有抛出任何异常。任何想法如何捕获超时异常？

I find a strange issue, when I connect to a very slow web site, and code path executes to "alert("connecting");", then I expect exception to be thrown for timeout, but in my debug, no exception is thrown. Any ideas how to catch timeout exception?

这是我的代码，

var index = 0;

function setup() {
    window.setInterval(PingWebSite, (10 * 1000));
}

function PingWebSite() {

    var http_request = new XMLHttpRequest();
    try {
        http_request.open("GET", "http://www.google.com", true);
        http_request.onreadystatechange = function() {
            if (http_request.readyState == 4) {
                if (http_request.status == 200) {
                    MonitorInformation.innerText = "http://www.google.com" + " Connection ok";
                    alert("ok");
                }
                else {
                    alert("fail");
                }
                http_request = null;
            } // if if (http_request.readyState == 4)
            else {
                // if execute here, no exception will be thrown
                alert("connecting");
            }
        }  // end of function
        http_request.send(null);
    } // try
    catch (e) {
        alert("service is not available");
    }
}

编辑1：我已按照这里的建议修改我的码。这是以下版本。新问题是索引值（例如0）将在ok / fail警告消息框之前的警报消息框中提示。我认为应该在ok / fail警告消息框后的警报消息框中提示索引值（例如0）。有什么想法吗？

EDIT 1: I have followed advice here to modify my code. Here is the below version. The new issue is index value (e.g. 0) will be prompted in alert message box before ok/fail alert message box. I think index value (e.g. 0) should be prompted in alert message box after ok/fail alert message box. Any ideas why?

var index = 0;
var http_request;
var xhrTimeout;
var chkConn;

function setup() {
    chkConn = window.setInterval(PingWebSite, (10 * 1000));
}

function WebMonitorTimeout() {
    http_request.abort();
    alert("timeout");
    index = index + 1;
}

function PingWebSite() {

    http_request = new XMLHttpRequest();
    http_request.open("GET", "http://www.google.com", true);

    http_request.onreadystatechange = function()
    {
        if (http_request.readyState == 4) {
            if (chkConn) { clearInterval(chkConn); }
            if (http_request.status == 200) {
                alert("ok");
                index = index + 1;
                if (xhrTimeout) { clearTimeout(xhrTimeout); }
            }
            else {
                alert("fail");
                index = index + 1;
                if (xhrTimeout) { clearTimeout(xhrTimeout); }
                }

                http_request = null;
            } //if (http_request.readyState == 4)

    }    // end of event function
    http_request.send(null);
    xhrTimeout = setTimeout("WebMonitorTimeout();", 30000);
    alert(index);
    chkConn = window.setInterval(PingWebSite, (30 * 1000));
}

提前感谢，
George

thanks in advance, George

推荐答案

重复 javascript连接到网站代码无法正常工作

由于浏览器安全，您无法执行跨站点XHR请求

You can't do Cross Site XHR requests because of browser security

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