XMLHttpRequest多次启动，而不启动onreadystatechange函数

Question

有问题的用户脚本：http ://userscripts.org/scripts/show/130532

在将其创建的网站更新为HTML5之后，我不得不更新脚本。但是，现在有一个很大的问题。当我启动包含XMLHttpRequest的脚本的主要功能时，它只是向这些控制台发送垃圾邮件，直到浏览器崩溃。

现在，我在StackOverflow和Google中四处寻找可以帮助我的东西，但是没有任何帮助。

如果继续尝试该脚本，请小心，因为它会使浏览器崩溃。至少在FF 11.00中对我有用

码：

// ==UserScript==
// @name           Where my thread at
// @include        *//boards.4chan.org/*/res/*
// ==/UserScript==

(function () {
    "use strict";
    var board = document.location.href.match(/https?:\/\/boards\.4chan\.org\/[\w]+/i), threadNo = location.pathname.match(/\/res\/([\d]+)/i), main = document.getElementsByName("delform")[0], is404 = 0, ttt = null, b, c, num, timer, html, i, l, no, found, xhr1, xhr2, cstatus, ui, pg;

    function lookup(resp) {
        html = resp.match(/<div class="postContainer opContainer".*?<\/div>[^<]*?<\/div>/gi);
        if (html) {
            l = html.length;
            for (i = 0; i < l; i += i) {
                no = html[i].match(/<a href="res\/([\d]+)"/i)[1];
                if (threadNo[1] === no) {
                    document.getElementById('page').innerHTML = pg;
                    cstatus.innerHTML = "Status:&nbsp;Done";
                    found = 1;
                    break;
                }
            }
        }
    }

    function doIndex(pg) {
        b = document.getElementById('shouldi');
        if (!is404 && b.checked === true) {
            cstatus.innerHTML = "Status:&nbsp;Searching";
            c = document.getElementById('timerbox');
            num = parseInt(c.value, 10);
            if (num > 600) { timer = 600; }
            if (num < 30) { timer = 30; }
            if (isNaN(num)) {
                timer = 60;
                alert("Value entered is not a valid number! Defaulting to 60");
                c.value = "60";
            }
            if (!timer) { timer = num; }
            xhr1 = new XMLHttpRequest();
            xhr1.open("GET", board[0] + (0 === pg ? "" : "/" + pg), true);
            xhr1.setRequestHeader("Cache-Control", "no-cache");
            xhr1.onreadystatechange = function () {
                if (xhr1.readyState === 4) {
                    if (xhr1.status === 200) {
                        lookup(xhr1.responseText);
                    }
                }
                if (found) {
                    ttt = setTimeout(function () {
                        doIndex(0);
                    }, timer * 1000);
                } else {
                    if (pg < 15) {
                        doIndex(pg + 1);
                    } else {
                        cstatus.innerHTML = "Status:&nbsp;Really 404?";
                        xhr2 = new XMLHttpRequest();
                        xhr2.open("GET", board[0] + threadNo[0], true);
                        xhr2.setRequestHeader("Cache-Control", "no-cache");
                        xhr2.onreadystatechange = function () {
                            if (xhr2.readyState === 4) {
                                if (xhr2.status === 404) {
                                    cstatus.parentNode.removeChild(cstatus);
                                    document.getElementById('page').innerHTML = "404'd";
                                    is404 = 1;
                                } else {
                                    cstatus.innerHTML = "Status:&nbsp;Still alive";
                                    setTimeout(function () {
                                        doIndex(0);
                                    }, 1000);
                                }
                            }
                        };
                        xhr2.send(null);
                    }
                }
            };
            xhr1.send(null);
        }
    }

    ui = document.createElement('center');
    ui.innerHTML = '<table border="0" style="width: 100%"><tbody><tr><td style="width: 33%;text-align: right;">Timer(600-30s):&nbsp;<input type="text" value="30" maxlength="3" size="3" id="timerbox">&nbsp;&nbsp;</td><td style="width: 33%">&nbsp;<center><font size="20" color="red" id="page">&nbsp;</font></center>&nbsp;</td><td style="width: 33%;text-align:left;">&nbsp;&nbsp;<span id="checkcheck"><label for="shouldi">Checking</label><input type="checkbox" id="shouldi" /></span>&nbsp;&nbsp;<span id="checkstatus">Status:&nbsp;</span></td></tr></tbody></table>';
    main.parentNode.insertBefore(ui, main);
    cstatus = document.getElementById('checkstatus');
    cstatus.innerHTML = "Status:&nbsp;Ready";
    document.getElementById('checkcheck').addEventListener("click", function () {
        if (ttt !== null) {
            clearTimeout(ttt);
            ttt = null;
        }
        setTimeout(function () {
            doIndex(0);
        }, 500);
    }, false);
}());

Answer 1

您正在使用几个变量，而没有在本地声明它们：

var ..., found, xhr1, xhr2, cstatus, ui, pg;
...
function doIndex(pg) {
    ...
        xhr1 = new XMLHttpRequest();
     // ^^^^ No var !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
        ...
        xhr1.onreadystatechange = function() {
            if (xhr1.readyState === 4) { ... }
            if (found) {
                ...
            } else {
                if (pg < 15) {
                    doIndex(pg + 1); // <-- !!!!!!!!!!!!!!!!!!
                } else { ...
                    xhr2 = new XMLHttpRequest();
                    ...
                    xhr2.onreadystatechange = function() { ... };
                    xhr2.send(null);
                }
            }
        };
        xhr1.send(null);
    }
}  ...
doIndex(0); // Initiate the doom

首先，您将一个新的XHR实例分配给一个非局部xhr1变量。
然后，添加一个readystatechange事件处理程序，其中将发生以下情况：

1. 最初readyState不是4，所以found是假。由于pg从0开始，因此doIndex(pg + 1)被调用。现在，xhr1被新的XHR实例覆盖。
2. 这一直持续到pg15岁。然后pg < 15为false，然后恐怖开始了：
   • xhr1.onreadystatechange在请求期间触发多次。pg < 15为假，因此对else块进行了评估，您在其中启动了几个新的XHR（xhr2）请求...
   • 由于请求尚未完成，因此所有以前的readystatechange事件仍然会触发。在每个事件处理程序中，您都在比较的值xhr1.readyState，该值指的是最后创建的xhr1请求的状态。
     因此，您要doIndex(pg+1)一遍又一遍地调用，一旦pg达到15，就会创建新的XHR（xhr2）实例。

要解决此问题，请在函数中声明变量，然后将整个onreadystatechange块包装起来if (xhr1.readyState == 4)（或使用onload代替onreadystatechange）。

function dIndex(pg) {
    var xhr1, xhr2;
    ...
    xhr1.onreadystatechange = function() {
        if (xhr1.readyState === 4) {
           /* ... */
        }
    };
    ...