新手村27 - Click and Drag

11th鐵人賽 javascript 前端新手村

Chester

2019-10-12 13:05:31

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27 - Click and Drag

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
- 拖拉互動要有拖拉畫面的功能
畫面
- 拖拉的程度要和畫面移動程度相同的px

index_START.html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Click and Drag</title>
  <link rel="stylesheet" href="style.css">
</head>
<body>
  <div class="items">
    <div class="item item1">01</div>
    <div class="item item2">02</div>
    <div class="item item3">03</div>
    <div class="item item4">04</div>
    <div class="item item5">05</div>
    <div class="item item6">06</div>
    <div class="item item7">07</div>
    <div class="item item8">08</div>
    <div class="item item9">09</div>
    <div class="item item10">10</div>
    <div class="item item11">11</div>
    <div class="item item12">12</div>
    <div class="item item13">13</div>
    <div class="item item14">14</div>
    <div class="item item15">15</div>
    <div class="item item16">16</div>
    <div class="item item17">17</div>
    <div class="item item18">18</div>
    <div class="item item19">19</div>
    <div class="item item20">20</div>
    <div class="item item21">21</div>
    <div class="item item22">22</div>
    <div class="item item23">23</div>
    <div class="item item24">24</div>
    <div class="item item25">25</div>
  </div>

<script>
</script>

  </body>
</html>

CSS_START.html

html {
  box-sizing: border-box;
  background: url('https://source.unsplash.com/NFs6dRTBgaM/2000x2000') fixed;
  background-size: cover;
}

*, *:before, *:after {
  box-sizing: inherit;
}

body {
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  font-family: sans-serif;
  font-size: 20px;
  margin: 0;
}

.items {
  height: 800px;
  padding: 100px;
  width: 100%;
  border: 1px solid white;
  overflow-x: scroll;
  overflow-y: hidden;
  white-space: nowrap;
  user-select: none;
  cursor: pointer;
  transition: all 0.2s;
  transform: scale(0.98);
  will-change: transform;
  position: relative;
  background: rgba(255,255,255,0.1);
  font-size: 0;
  perspective: 500px;
}

.items.active {
  background: rgba(255,255,255,0.3);
  cursor: grabbing;
  cursor: -webkit-grabbing;
  transform: scale(1);
}

.item {
  width: 200px;
  height: calc(100% - 40px);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-size: 80px;
  font-weight: 100;
  color: rgba(0,0,0,0.15);
  box-shadow: inset 0 0 0 10px rgba(0,0,0,0.15);
}

.item:nth-child(9n+1) { background: dodgerblue;}
.item:nth-child(9n+2) { background: goldenrod;}
.item:nth-child(9n+3) { background: paleturquoise;}
.item:nth-child(9n+4) { background: gold;}
.item:nth-child(9n+5) { background: cadetblue;}
.item:nth-child(9n+6) { background: tomato;}
.item:nth-child(9n+7) { background: lightcoral;}
.item:nth-child(9n+8) { background: darkslateblue;}
.item:nth-child(9n+9) { background: rebeccapurple;}

.item:nth-child(even) { transform: scaleX(1.31) rotateY(40deg); }
.item:nth-child(odd) { transform: scaleX(1.31) rotateY(-40deg); }

JS - step by step

首先，一樣也是透過 querySelector 選取 Class items，可以將到所有的卡片外的 div

<script>
  const slider = document.querySelector('.items');
  console.log(slider);
  // 抓到25個div
</script>

並先來把觸發對象和條件先建構出來吧！在這個範例中，我們會分別用到 mousedown 、mousemove 、mouseup 三個觸發事件，分別是當滑鼠按下、移動、按起來事件會被觸發。

<script>
  const slider = document.querySelector('.items');
  console.log(slider);
  // 抓到25個div
  
  slider.addEventListener('mousedown', (e) => {});
	slider.addEventListener('mouseup', (e) => {});
	slider.addEventListener('mousemove', (e) => {});

</script>

先來判斷使用者是不是按下按鈕的，宣告變數 isDown 來判斷使用者有沒有按下滑鼠，預設一開始為 false，當使用者 mousedown 的時候表示按下， isDown = true ，使用者 mouseup 的時候表示按起， isDown = false，而在 mousemove 的能持續觸發事件的時候，應該判斷使用者是不是在按下的情況，否則應該停止 Function

<script>
  const slider = document.querySelector('.items');
  console.log(slider);
	let isDown = false;
  // 抓到25個div
  
  slider.addEventListener('mousedown', (e) => {
		isDown = true;
	});
	slider.addEventListener('mouseup', (e) => {
		isDown = false;
	});
	slider.addEventListener('mousemove', (e) => {
		if (!isDown) return;
	});

</script>

接下來我們透過加上 Class active 來產生特效，分別在滑鼠按下及按起時候新增移除 Class

<script>
  const slider = document.querySelector('.items');
  console.log(slider);
	let isDown = false;
  // 抓到25個div
  
  slider.addEventListener('mousedown', (e) => {
		isDown = true;
		slider.classList.add('active');
	});
	slider.addEventListener('mouseup', (e) => {
		isDown = false;
		slider.classList.remove('active');
	});
	slider.addEventListener('mousemove', (e) => {
		if (!isDown) return;
	});

</script>

最後再記錄現在的 offsetX & pageX 為變數 startX ，slider.scrollLeft 為變數 scrollLeft，最後在移動X軸時處理位置即可～

<script>
  const slider = document.querySelector('.items');
  console.log(slider);
  let isDown = false;
  let startX;
  let scrollLeft;

  slider.addEventListener('mousedown', (e) => {
    isDown = true;
    slider.classList.add('active');
    startX = e.pageX + slider.offsetLeft;
    scrollLeft = slider.scrollLeft;
  }); 

  slider.addEventListener('mouseup', (e) => {
    isDown = false;
    slider.classList.remove('active');
  });

  slider.addEventListener('mousemove', (e) => {
    if (!isDown) return;
    e.preventDefault();
    const x = e.pageX - slider.offsetLeft;
    const walk = (x - startX) * 3;
    slider.scrollLeft = scrollLeft - walk;
  });

</script>

就大功告成啦！

JS - final

<script>
  const slider = document.querySelector('.items');
  console.log(slider);
  let isDown = false;
  let startX;
  let scrollLeft;

  slider.addEventListener('mousedown', (e) => {
    isDown = true;
    slider.classList.add('active');
    startX = e.pageX + slider.offsetLeft;
    scrollLeft = slider.scrollLeft;
  }); 

  slider.addEventListener('mouseup', (e) => {
    isDown = false;
    slider.classList.remove('active');
  });

  slider.addEventListener('mousemove', (e) => {
    if (!isDown) return;
    e.preventDefault();
    const x = e.pageX - slider.offsetLeft;
    const walk = (x - startX) * 3;
    slider.scrollLeft = scrollLeft - walk;
  });

</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