# JS30-Day27-Click & Drag
- Ref : https://javascript30.com/

> By Jason

---

### html 結構

  <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>

---

### css

    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); }

### JavaScript

  const slider = document.querySelector('.items');
  let isDown = false;
  let startX;
  let scrollLeft;

  slider.addEventListener('mousedown', (e) => {
    isDown = true;
    slider.classList.add('active');
    startX = e.pageX - slider.offsetLeft; //  slider.offsetLeft 現在這東西會是 0
    scrollLeft = slider.scrollLeft;
    // console.log(e.pageX, slider.offsetLeft, scrollLeft)
  });

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

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

  slider.addEventListener('mousemove', (e) => {
    if (!isDown) return;  // stop the fn from running
    // e.preventDefault();
    const x = e.pageX - slider.offsetLeft;
    console.log(e.pageX, startX)
    const walk = x - startX;
    slider.scrollLeft = scrollLeft - walk;
  });

---
參考資料
[JS30-Day27-Click & Drag](https://ithelp.ithome.com.tw/articles/10197251)
[JS一秒區分clientX,offsetX,screenX,pageX之間關係](https://kknews.cc/zh-tw/news/r3pzzr.html)