javascript - 如何减慢 JavaScript 代码的执行速度？

Question

我正在编写一个脚本来删除我所有的 YouTube 评论。这段代码的每一行都可以删除一个注释，但是当我将其放入循环中时，我收到一个 Uncaught TypeError: Cannot read property 'click' of undefined ，当我运行时，它不会出现每行单独。我在想，如果我能找到一种在代码行之间休眠的方法，我就可以消除错误。

var myList = document.getElementsByClassName("dropdown-trigger style-scope ytd-menu-renderer");
for(i = 0; i < myList.length; i++) {
    myList[i].click();
    document.getElementsByClassName("style-scope ytd-menu-navigation-item-renderer")[4].click(); //error here
    document.getElementById("confirm-button").click();
}

我尝试使用 setTimeout，如下所示:

var myList = document.getElementsByClassName("dropdown-trigger style-scope ytd-menu-renderer");
for(i=0; i<myList.length; i++) {
    myList[i].click();
    setTimeout(function(){document.getElementsByClassName("style-scope ytd-menu-navigation-item-renderer")[4].click();}, 1000);
    setTimeout(function(){document.getElementById("confirm-button").click();}, 5000);
}

它返回了数字279，但没有错误，也没有删除评论。发生了什么？

Answer 1

以下所有选项都有点“hackish” - 但没有一致且简单的方法可以在点击事件完全处理后获得通知。您可以将自己的单击事件监听器添加到目标元素，但是随后可以通过 stopPropagation 将其“静音”...即使这样，也没有(简单)的方法可以知道 DOM 何时完成“重绘”作为点击事件的结果 - 你可以看看使用 MutationObserver ，我猜

我假设(永远不要这样做) document.getElementsByClassName("style-scope ytd-menu-navigation-item-renderer")[4] 所针对的元素通过单击 myList[i].click(); 动态添加这就是你遇到这个问题的原因。之后myList[i].click(); DOM 在“一段时间内”不会被“更新” - 所以，document.getElementsByClassName("style-scope ytd-menu-navigation-item-renderer")很容易失败。

A potential issue is if deleting comments changes the number of elements targeted by document.getElementsByClassName("dropdown-trigger style-scope ytd-menu-renderer"); - as HTMLCollections are "live", removing a DOM element will mutate the HTMLCollection - only the last two code snippets will be immune to this possibility

因此，您可以通过四种不同的方式来实现此目的

<小时/>

选项 1 - ES5，只是简单的回调

var DELAY = 0; // try 0, then try increasing values
var myList = document.getElementsByClassName("dropdown-trigger style-scope ytd-menu-renderer");
function confirmClick(callback3) {
    document.getElementById("confirm-button").click();
    setTimeout(callback3, DELAY);
}
function itemClick(callback2, callback3)  {
    document.getElementsByClassName("style-scope ytd-menu-navigation-item-renderer")[4].click();
    setTimeout(callback2, DELAY, callback3);
}
function listClick(element, callback1, callback2, callback3) {
    element.click();
    setTimeout(callback1, DELAY, callback2, callback3);
}
function doOne(i) {
    listClick(myList[i], itemClick, confirmClick, function() {
        ++i;
        if (i < myList.length) {
            doOne(i);
        }
    });
}
doOne(0);

<小时/>

As you are trying to "chain" multiple asynchronous (sort of) processes together, Promise's (seem) to make the code a little less cumbersome

选项 2 - Promise，但带有嵌套 setTimeout的-使用Array#reduce将点击链接在一起，以便它们严格地一个接一个地处理

这太丑了，真的很丑，让金字塔建筑留给死去的埃及人，包括来说明我想要实现的目标

var DELAY = 0; // try 0, then try increasing values
var myList = document.getElementsByClassName("dropdown-trigger style-scope ytd-menu-renderer");
var p = Promise.resolve();
for(i = 0; i < myList.length; i++) {
    myList[i].click();
    p = p.then(() => new Promise(resolve) => {
        setTimeout(() => {
            document.getElementsByClassName("style-scope ytd-menu-navigation-item-renderer")[4].click();
            setTimeout(() => {
                document.getElementById("confirm-button").click();
                setTimeout(resolve, DELAY);
            }, DELAY);
        }, DELAY);
    });
}

<小时/>

选项 3 - Promise 带有辅助函数 - 基本上是上面的代码，但添加了辅助函数来防止金字塔

const DELAY = 0; // try 0, then try increasing values
const clickThenDelay = element => new Promise(resolve => {
    element.click();
    setTimeout(resolve, DELAY);
});
var myList = document.getElementsByClassName("dropdown-trigger style-scope ytd-menu-renderer");

Array.from(myList).reduce((p, item) => { 
    return p
    .then(() => clickThenDelay(item))
    .then(() => clickThenDelay(document.getElementsByClassName("style-scope ytd-menu-navigation-item-renderer")[4]))
    .then(() => clickThenDelay(document.getElementById("confirm-button")))
}, Promise.resolve());

<小时/>

选项 4 - 与选项 3 类似，但此选项在触发单击之前添加了一个单击事件处理程序，该处理程序在“处理”单击后被删除。大概最后添加的处理程序是最后调用的。但不确定这是否得到保证。此外，如果较早的处理程序调用event.stop[Immediate]Propagation()，这将不起作用。

const DELAY = 0; // try 0, then try increasing values
const clickThenDelay = element => new Promise(resolve => {
    const handleClick = () => {
        element.removeEventListener('click', handleClick);
        setTimeout(resolve, DELAY); // wait for repaint? Perhaps a MutationObserver event could be useful here?
    }
    element.addEventListener('click', handleClick);
    element.click();
});
var myList = document.getElementsByClassName("dropdown-trigger style-scope ytd-menu-renderer");

Array.from(myList).reduce((p, item) => {
    return p
    .then(clickThenDelay(item))
    .then(() => clickThenDelay(document.getElementsByClassName("style-scope ytd-menu-navigation-item-renderer")[4]))
    .then(() => clickThenDelay(document.getElementById("confirm-button")))
}, Promise.resolve());