如何写好js|青训营笔记

这是我参与「第四届青训营 」笔记创作活动的的第7天

如何写好js

1，职能分离 html css js各司其职

2，进行组件封装

3，应用函数式编程思想

举例当实现图片白天模式与夜间两种模式

方法一

 const btn = document.getElementById('modeBtn');
  btn.addEventListener('click', (e) => {
    const body = document.body;
    if(e.target.innerHTML === '🌞') {
      body.style.backgroundColor = 'black';
      body.style.color = 'white';
      e.target.innerHTML = '🌜';
    } else {
      body.style.backgroundColor = 'white';
      body.style.color = 'black';
      e.target.innerHTML = '🌞';
    }
  });

方法二

 const btn = document.getElementById('modeBtn');
  btn.addEventListener('click', (e) => {
    const body = document.body;
    if(body.className !== 'night') {
      body.className = 'night';
    } else {
      body.className = '';
    }
  });

方法三

<input id="modeCheckBox" type="checkbox">
  <div class="content">
    <header>
      <label id="modeBtn" for="modeCheckBox"></label>
      <h1>深夜食堂</h1>
    </header>
    <main>
      <div class="pic">
        <img src="https://p2.ssl.qhimg.com/t0120cc20854dc91c1e.jpg">
      </div>
      <div class="description">
        <p>
            这是一间营业时间从午夜十二点到早上七点的特殊食堂。这里的老板，不太爱说话，却总叫人吃得热泪盈
            眶。一味追求事业成功的白领，在这里结交了真正暖心的朋友，发现真情比成功更有意义。食物、故事、真情，汇聚了整部剧的主题，教会人们坦然面对得失，对生活充满期许和热情。每一个故事背后都饱含深情，情节跌宕起伏，令人流连忘返 [6]  。
        </p>
      </div>
    </main>
  </div>

  #modeCheckBox {
    display: none;
  }

  #modeCheckBox:checked + .content {
    background-color: black;
    color: white;
    transition: all 1s;
  }

• HTML/CSS/JS 各司其责
• 应当避免不必要的由 JS 直接操作样式
• 可以用 class 来表示状态
• 纯展示类交互寻求零 JS 方案

组件封装

组件是指Web页面上抽出来一个个包含模版（HTML）、功能（JS）和样式（CSS）的单元。好的组件具备封装性、正确性、扩展性、复用性。

举例：用原生 JS 写一个电商网站的轮播图，应该怎么实现？

<div id="my-slider" class="slider-list">
      <ul>
        <li class="slider-list__item--selected">
          <img src="https://p5.ssl.qhimg.com/t0119c74624763dd070.png">
        </li>
        <li class="slider-list__item">
          <img src="https://p4.ssl.qhimg.com/t01adbe3351db853eb3.jpg">
        </li>
        <li class="slider-list__item">
          <img src="https://p2.ssl.qhimg.com/t01645cd5ba0c3b60cb.jpg">
        </li>
        <li class="slider-list__item">
          <img src="https://p4.ssl.qhimg.com/t01331ac159b58f5478.jpg">
        </li>
      </ul>
    </div>

#my-slider{
    position: relative;
    width: 790px;
  }

  .slider-list ul{
    list-style-type:none;
    position: relative;
    padding: 0;
    margin: 0;
  }

  .slider-list__item,
  .slider-list__item--selected{
    position: absolute;
    transition: opacity 1s;
    opacity: 0;
    text-align: center;
  }

  .slider-list__item--selected{
    transition: opacity 1s;
    opacity: 1;
  }

 class Slider{
    constructor(id){
      this.container = document.getElementById(id);
      this.items = this.container
      .querySelectorAll('.slider-list__item, .slider-list__item--selected');
    }
    getSelectedItem(){
      const selected = this.container
        .querySelector('.slider-list__item--selected');
      return selected
    }
    getSelectedItemIndex(){
      return Array.from(this.items).indexOf(this.getSelectedItem());
    }
    slideTo(idx){
      const selected = this.getSelectedItem();
      if(selected){ 
        selected.className = 'slider-list__item';
      }
      const item = this.items[idx];
      if(item){
        item.className = 'slider-list__item--selected';
      }
    }
    slideNext(){
      const currentIdx = this.getSelectedItemIndex();
      const nextIdx = (currentIdx + 1) % this.items.length;
      this.slideTo(nextIdx);
    }
    slidePrevious(){
      const currentIdx = this.getSelectedItemIndex();
      const previousIdx = (this.items.length + currentIdx - 1)
        % this.items.length;
      this.slideTo(previousIdx);  
    }
  }

  const slider = new Slider('my-slider');
  slider.slideTo(3);