新手村22 - Follow Along Link Highlighter

11th鐵人賽前端新手村 javascript

Chester

2019-10-07 01:53:54

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22 - Follow Along Link Highlighter

俗話說的好，一天一蘋果，醫生遠離我

一天一 JS，What the f*ck JavaScript？

small steps every day - 記錄著新手村日記

完成目標

功能
- 超連結Hover時，白色區塊要出現在該超連結區塊上
畫面
- 白色區塊的寬高要符合該超連結區塊
- 滑鼠進入另一個超連結區塊時，白色的區塊不會消失

index_START.html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>???Follow Along Nav</title>
  <link rel="stylesheet" href="style.css">
</head>
<body>

    <nav>
      <ul class="menu">
        <li><a href="">Home</a></li>
        <li><a href="">Order Status</a></li>
        <li><a href="">Tweets</a></li>
        <li><a href="">Read Our History</a></li>
        <li><a href="">Contact Us</a></li>
      </ul>
    </nav>

    <div class="wrapper">
      <p>Lorem ipsum dolor sit amet, <a href="">consectetur</a> adipisicing elit. Est <a href="">explicabo</a> unde natus necessitatibus esse obcaecati distinctio, aut itaque, qui vitae!</p>
      <p>Aspernatur sapiente quae sint <a href="">soluta</a> modi, atque praesentium laborum pariatur earum <a href="">quaerat</a> cupiditate consequuntur facilis ullam dignissimos, aperiam quam veniam.</p>
      <p>Cum ipsam quod, incidunt sit ex <a href="">tempore</a> placeat maxime <a href="">corrupti</a> possimus <a href="">veritatis</a> ipsum fugit recusandae est doloremque? Hic, <a href="">quibusdam</a>, nulla.</p>
      <p>Esse quibusdam, ad, ducimus cupiditate <a href="">nulla</a>, quae magni odit <a href="">totam</a> ut consequatur eveniet sunt quam provident sapiente dicta neque quod.</p>
      <p>Aliquam <a href="">dicta</a> sequi culpa fugiat <a href="">consequuntur</a> pariatur optio ad minima, maxime <a href="">odio</a>, distinctio magni impedit tempore enim repellendus <a href="">repudiandae</a> quas!</p>
    </div>

  <script>
    // ???????????????
  </script>
</body>
</html>

JS - step by step

首先，透過 querySelectorAll 將所有的 a 連結都找出來吧（這步驟應該很熟練了而且會是一個 NodeList(19) ），並且將帶有 Class highlight 的 span 附加在 body 上，這邊作者想表達的意思應該是可以透過 JS 來建立元素、新增Class 及寫進 HTML 之中

<script>
    // ???????????????
    const triggers = document.querySelectorAll('a');
    console.log(triggers);
    const highlight = document.createElement('span');
    console.log(highlight);
    highlight.classList.add('highlight');
    document.body.appendChild(highlight);  
</script>

接下來，每當使用者滑鼠移動到連結上就會觸發 mouseenter 事件，概念與 mouseover 大致相同，唯一的差別在於並不會冒泡

mouseenter：https://tinyurl.com/y6g3x4cs

<script>
    // ???????????????
    const triggers = document.querySelectorAll('a');
    console.log(triggers);
    const highlight = document.createElement('span');
    console.log(highlight);
    highlight.classList.add('highlight');
    document.body.appendChild(highlight); 
    
    function highlightLink() {

    }

    triggers.forEach(a => a.addEventListener('mouseenter', highlightLink));
</script>

當使用者觸發事件後，會呼叫 highlightLink 方法，其中會回傳 Element.getBoundingClientRect() 的 DOMRect 返回值對象，一組矩形的集合

Element.getBoundingClientRect()：https://tinyurl.com/yyxcclg7

<script>
    // ???????????????
    const triggers = document.querySelectorAll('a');
    console.log(triggers);
    const highlight = document.createElement('span');
    console.log(highlight);
    highlight.classList.add('highlight');
    document.body.appendChild(highlight); 
    
    function highlightLink() {
      const linkCoords = this.getBoundingClientRect();
      console.log(linkCoords);
    }

    triggers.forEach(a => a.addEventListener('mouseenter', highlightLink));
</script>

將回傳的長、寬、Ｘ軸、Ｙ軸設為變數 coords

<script>
    // ???????????????
    const triggers = document.querySelectorAll('a');
    console.log(triggers);
    const highlight = document.createElement('span');
    console.log(highlight);
    highlight.classList.add('highlight');
    document.body.appendChild(highlight); 
    
    function highlightLink() {
      const linkCoords = this.getBoundingClientRect();
      console.log(linkCoords);
      const coords = {
      	width: linkCoords.width,
      	height: linkCoords.height,
      	top: linkCoords.top + window.scrollY,
      	left: linkCoords.left + window.scrollX
    	};
    }

    triggers.forEach(a => a.addEventListener('mouseenter', highlightLink));
</script>

再當滑鼠滑到連結上時附加CSS

<script>
    // ???????????????
    const triggers = document.querySelectorAll('a');
    console.log(triggers);
    const highlight = document.createElement('span');
    console.log(highlight);
    highlight.classList.add('highlight');
    document.body.appendChild(highlight); 
    
    function highlightLink() {
      const linkCoords = this.getBoundingClientRect();
      console.log(linkCoords);
      const coords = {
      	width: linkCoords.width,
      	height: linkCoords.height,
      	top: linkCoords.top + window.scrollY,
      	left: linkCoords.left + window.scrollX
    	};
    	
    	highlight.style.width = `${coords.width}px`;
    	highlight.style.height = `${coords.height}px`;
    	highlight.style.transform = `translate(${coords.left}px, ${coords.top}px)`;
    	//DOMRect {x: 666.93359375, y: 100, width: 93.8671875, height: 32.5, top: 100, …}
    }

    triggers.forEach(a => a.addEventListener('mouseenter', highlightLink));
</script>

就大功告成啦！

JS - final

<script>
    // ???????????????
    const triggers = document.querySelectorAll('a');
    console.log(triggers);
    const highlight = document.createElement('span');
    console.log(highlight);
    highlight.classList.add('highlight');
    document.body.appendChild(highlight); 
    
    function highlightLink() {
      const linkCoords = this.getBoundingClientRect();
      console.log(linkCoords);
      const coords = {
      	width: linkCoords.width,
      	height: linkCoords.height,
      	top: linkCoords.top + window.scrollY,
      	left: linkCoords.left + window.scrollX
    	};
    	
    	highlight.style.width = `${coords.width}px`;
    	highlight.style.height = `${coords.height}px`;
    	highlight.style.transform = `translate(${coords.left}px, ${coords.top}px)`;
    }

    triggers.forEach(a => a.addEventListener('mouseenter', highlightLink));
</script>

本刊同步於個人網站：http://chestertang.site/

本次範例程式碼原作者來源：https://tinyurl.com/yavm5f5n