Question

如果我按下A或S这样的按键按钮几秒钟而不抬起我的手指，那么转换效果就会“sticks”。并且玩的类别没有被删除。如果我只是点击A，则添加播放类，然后删除。我注意到，如果我评论出某个声明，它的作用就像它应该的那样。为什么？（添加注释掉的语句以查看我的意思）。

https://codepen.io/anon/pen/dWpxqg

＆＃13;

// If i keep a key button like A or S pressed down all the time, eventually the transform effect (yellow border appearing) doesn't go away. If i simply tap A a class of Playing is added and then removed. I noticed that if i comment out a certain statement it works like it's supposed to. Why?



function removeTransition(e) {
    // COMMENTED STATEMENT BELOW IS PROBLEMATIC.
    // if(e.propertyName !== 'transform') return;
    this.classList.remove('playing');
}
function playSound(e) {
    const key = document.querySelector(`.key[data-key="${e.keyCode}"]`);
    const audio = document.querySelector(`audio[data-key="${e.keyCode}"]`);
    if(!audio) return;
    audio.currentTime = 0;
    audio.play();
    key.classList.add('playing');
}

const keys = document.querySelectorAll('.key');
keys.forEach(key => key.addEventListener('transitionend', removeTransition));
window.addEventListener('keydown', playSound);

＆＃13;

html {
  box-sizing: border-box; }

*,
*:before,
*:after {
  box-sizing: inherit; }

html {
  height: 100%; }
  html body {
    margin: 0;
    padding: 0;
    min-height: 100%;
    color: white; }

.root {
  display: flex;
  flex-direction: column;
  height: 100vh;
  text-align: center;
  background: url("../img/crowd.jpg") bottom center;
  background-size: cover; }

.section {
  display: flex;
  justify-content: center;
  align-items: center;
  flex: 1; }

.key {
  display: inline-block;
  margin: 10px;
  width: 80px;
  border: 5px solid black;
  border-radius: 5px;
  transition: all .7s ease;
  background-color: rgba(0, 0, 0, 0.4); }
  .key kbd {
    padding: 5px 10px 0 10px;
    display: block;
    font-size: 3rem; }
  .key span {
    color: gold;
    padding-bottom: 10px;
    text-transform: uppercase;
    letter-spacing: 1px;
    font-size: 0.7rem;
    font-weight: 700;
    font-family: sans-serif; }

.playing {
  transform: scale(1.1);
  border-color: #ffc600;
  box-shadow: 0 0 1rem #ffc600; }

.k-grp-1 {
  display: flex;
  justify-content: space-between; }

footer {
  background-color: #303F9F; }

＆＃13;

<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <link rel="stylesheet" href="css/styles.css">
</head>

<body>
    <div class="root">
        <section class="section">
            <div class="keys">
                <div class="k-grp-1">
                    <div data-key="65" class="key">
                        <kbd>A</kbd>
                        <span class="sound">clap</span>
                    </div>
                    <div data-key="83" class="key">
                        <kbd>S</kbd>
                        <span class="sound">hihat</span>
                    </div>
                    <div data-key="68" class="key">
                        <kbd>D</kbd>
                        <span class="sound">kick</span>
                    </div>
                    <div data-key="70" class="key">
                        <kbd>F</kbd>
                        <span class="sound">openhat</span>
                    </div>


                    <div data-key="71" class="key">
                        <kbd>G</kbd>
                        <span class="sound">boom</span>
                    </div>
                </div>
                <div class="k-grp-2">
                    <div data-key="72" class="key">
                        <kbd>H</kbd>
                        <span class="sound">ride</span>
                    </div>
                    <div data-key="74" class="key">
                        <kbd>J</kbd>
                        <span class="sound">snare</span>
                    </div>
                    <div data-key="75" class="key">
                        <kbd>K</kbd>
                        <span class="sound">tom</span>
                    </div>
                    <div data-key="76" class="key">
                        <kbd>L</kbd>
                        <span class="sound">tink</span>
                    </div>
                </div>
            </div>
        </section>
        <footer> Footer</footer>
    </div>

    <audio data-key="65" src="sounds/clap.wav"></audio>
    <audio data-key="83" src="sounds/hihat.wav"></audio>
    <audio data-key="68" src="sounds/kick.wav"></audio>
    <audio data-key="70" src="sounds/openhat.wav"></audio>
    <audio data-key="71" src="sounds/boom.wav"></audio>
    <audio data-key="72" src="sounds/ride.wav"></audio>
    <audio data-key="74" src="sounds/snare.wav"></audio>
    <audio data-key="75" src="sounds/tom.wav"></audio>
    <audio data-key="76" src="sounds/tink.wav"></audio>

    <script src="js/main.js"></script>
</body>

</html>

＆＃13;

Answer 1

我将尝试通过在事件回调中添加几行来演示特定条件语句的问题，如下所示：

var counts = {};

function removeTransition (e) {

    // if ( (e.propertyName === 'transform') ) {
    //  return;
    // }

    if (typeof counts[e.propertyName] === 'undefined') {
        counts[e.propertyName] = 1;
    } else {
        counts[e.propertyName] = counts[e.propertyName] + 1;
    }

    // console.log(e.propertyName);
    this.classList.remove('playing');

    console.log(counts);
}

我只是添加了一张地图，以便在按住按钮的同时跟踪 e.propertyName 属性可以拥有的不同值的不同数量。

例如，如果我按住'A'键5“然后停止我得到以下测量：

{
  "transform": 29,
  "border-right-color": 58,
  "border-bottom-color": 58,
  "border-left-color": 58,
  "border-top-color": 58,
  "box-shadow": 30
}

正如您将注意到的那样， removeTransition（）函数被调用的总次数 - 由 transitionend 事件触发 - 转换与其他CSS属性相比，值几乎发生了一半的时间。

这意味着如果有人按下按钮（无论多长时间）， keydown 事件将被持续触发并且正在播放类将在转向添加到元素。但问题是，如果您只检查要接收的'transform' CSS属性，那么与其他CSS属性相比，它将捕获一半的时间，主要是由于它的异步性质，因为它需要更长的时间才能完成。

为什么这个陈述有问题？

1 个答案: