第六届360前端星计划_JavaScript 从入门到放弃

2020-04-09 本文已影响0人 lhang_91ad

主讲人

月影
360前端技术专家
奇舞团

各司其职

关灯吃面例子：

版本一
light.onclick = function(evt) {
  if(light.style.backgroundColor !== 'green'){
    document.body.style.backgroundColor = '#000';
    document.body.style.color = '#fff';
    light.style.backgroundColor = 'green';
  }else{
    document.body.style.backgroundColor = '';
    document.body.style.color = '';
    light.style.backgroundColor = '';    
  }
}
//js直接操作css，违反各司其职原则

lightButton.onclick = function(evt) {
  if(main.className === 'light-on'){
    main.className = 'light-off';
  }else{
    main.className = 'light-on';
  }
}
//通过修改类名，没有直接操作但是js还是有可能有bug

html,body {
  margin: 0;
  padding: 0;
  width: 100%;
  height: 100%;
}

#light {
  display: none;
}

#main {
  position: relative;
  padding: 20px;
  width: 100%;
  height: 100%;
  background-color: #fff;
  color: #000;
  transition: all .5s;
}

#light:checked + #main {
  background-color: #000;
  color: #fff;
}

.pic {
  float: left;
  margin-right: 20px;
}
//通过css实现，但是有兼容性问题

<input id="light" type="checkbox"></input>
<div id="main">
  <div class="pic">
    <img src="https://p4.ssl.qhimg.com/t01e932bf06236f564f.jpg">
  </div>
  <div class="content">
    <pre>
今天回到家，
煮了点面吃，
一边吃面一边哭，
泪水滴落在碗里，
没有开灯。
    </pre>
  </div>
  <label for="light">
    <span id="lightButton"> </span>
  <label>
</div>

复杂 UI 组件的设计

以轮播图为例介绍UI设计

结构设计

<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>
//1. 图片结构是一个列表型结构，所以主体用 <ul>
//2. 使用 css 绝对定位将图片重叠在同一个位置
//3. 轮播图切换的状态使用修饰符（modifier）
//4. 轮播图的切换动画使用 css transition

API 设计

getSlectedItem()
getSlectedItemIndex()
slidTo()
slideNext()
slidePrevious()

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');
setInterval(() => {
  slider.slideNext()
}, 3000)

控制流设计

<a class="slide-list__next"></a>
  <a class="slide-list__previous"></a>
  <div class="slide-list__control">
    <span class="slide-list__control-buttons--selected"></span>
    <span class="slide-list__control-buttons"></span>
    <span class="slide-list__control-buttons"></span>
    <span class="slide-list__control-buttons"></span>
  </div>

const detail = {index: idx}
const event = new CustomEvent('slide', {bubbles:true, detail})
this.container.dispatchEvent(event)
//用自定义事件进行触发

具体实现

class Slider{
  constructor(id, cycle = 3000){
    this.container = document.getElementById(id);
    this.items = this.container.querySelectorAll('.slider-list__item, .slider-list__item--selected');
    this.cycle = cycle;
const controller = this.container.querySelector('.slide-list__control');
if(controller){
  const buttons = controller.querySelectorAll('.slide-list__control-buttons, .slide-list__control-buttons--selected');
  controller.addEventListener('mouseover', evt=>{
    const idx = Array.from(buttons).indexOf(evt.target);
    if(idx >= 0){
      this.slideTo(idx);
      this.stop();
    }
  });
  
  controller.addEventListener('mouseout', evt=>{
    this.start();
  });
  
  this.container.addEventListener('slide', evt => {
    const idx = evt.detail.index
    const selected = controller.querySelector('.slide-list__control-buttons--selected');
    if(selected) selected.className = 'slide-list__control-buttons';
    buttons[idx].className = 'slide-list__control-buttons--selected';
  })
}

const previous = this.container.querySelector('.slide-list__previous');
if(previous){
  previous.addEventListener('click', evt => {
    this.stop();
    this.slidePrevious();
    this.start();
    evt.preventDefault();
  });
}

const next = this.container.querySelector('.slide-list__next');
if(next){
  next.addEventListener('click', evt => {
    this.stop();
    this.slideNext();
    this.start();
    evt.preventDefault();
  });
}
}
  getSelectedItem(){
    let selected = this.container.querySelector('.slider-list__item--selected');
    return selected
  }
  getSelectedItemIndex(){
    return Array.from(this.items).indexOf(this.getSelectedItem());
  }
  slideTo(idx){
    let selected = this.getSelectedItem();
    if(selected){ 
      selected.className = 'slider-list__item';
    }
    let item = this.items[idx];
    if(item){
      item.className = 'slider-list__item--selected';
    }
const detail = {index: idx}
const event = new CustomEvent('slide', {bubbles:true, detail})
this.container.dispatchEvent(event)
slideNext(){
    let currentIdx = this.getSelectedItemIndex();
    let nextIdx = (currentIdx + 1) % this.items.length;
    this.slideTo(nextIdx);
  }
  slidePrevious(){
    let currentIdx = this.getSelectedItemIndex();
    let previousIdx = (this.items.length + currentIdx - 1) % this.items.length;
    this.slideTo(previousIdx);  
  }
  start(){
    this.stop();
    this._timer = setInterval(()=>this.slideNext(), this.cycle);
  }
  stop(){
    clearInterval(this._timer);
  }
}

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

优化1.：插件/依赖注入

通过plugin注册函数

class Slider{
  constructor(id, cycle = 3000){
    this.container = document.getElementById(id);
    this.items = this.container.querySelectorAll('.slider-list__item, .slider-list__item--selected');
    this.cycle = cycle;
  }
  registerPlugins(...plugins){
    plugins.forEach(plugin => plugin(this));
  }
  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';
    }

    const detail = {index: idx}
    const event = new CustomEvent('slide', {bubbles:true, detail})
    this.container.dispatchEvent(event)
  }
  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);  
  }
  addEventListener(type, handler){
    this.container.addEventListener(type, handler)
  }
  start(){
    this.stop();
    this._timer = setInterval(()=>this.slideNext(), this.cycle);
  }
  stop(){
    clearInterval(this._timer);
  }
}

function pluginController(slider){
  const controller = slider.container.querySelector('.slide-list__control');
  if(controller){
    const buttons = controller.querySelectorAll('.slide-list__control-buttons, .slide-list__control-buttons--selected');
    controller.addEventListener('mouseover', evt=>{
      const idx = Array.from(buttons).indexOf(evt.target);
      if(idx >= 0){
        slider.slideTo(idx);
        slider.stop();
      }
    });

    controller.addEventListener('mouseout', evt=>{
      slider.start();
    });

    slider.addEventListener('slide', evt => {
      const idx = evt.detail.index
      const selected = controller.querySelector('.slide-list__control-buttons--selected');
      if(selected) selected.className = 'slide-list__control-buttons';
      buttons[idx].className = 'slide-list__control-buttons--selected';
    });
  }  
}

function pluginPrevious(slider){
  const previous = slider.container.querySelector('.slide-list__previous');
  if(previous){
    previous.addEventListener('click', evt => {
      slider.stop();
      slider.slidePrevious();
      slider.start();
      evt.preventDefault();
    });
  }  
}

function pluginNext(slider){
  const next = slider.container.querySelector('.slide-list__next');
  if(next){
    next.addEventListener('click', evt => {
      slider.stop();
      slider.slideNext();
      slider.start();
      evt.preventDefault();
    });
  }  
}


const slider = new Slider('my-slider');
slider.registerPlugins(pluginController, pluginPrevious, pluginNext);
slider.start();

优化2：改进插件
[图片上传失败...(image-37aaae-1586444695444)]

class Slider{
  constructor(id, opts = {images:[], cycle: 3000}){
    this.container = document.getElementById(id);
    this.options = opts;
    this.container.innerHTML = this.render();
    this.items = this.container.querySelectorAll('.slider-list__item, .slider-list__item--selected');
    this.cycle = opts.cycle || 3000;
    this.slideTo(0);
  }
  render(){
    const images = this.options.images;
    const content = images.map(image => `
      <li class="slider-list__item">
        <img src="${image}"/>
      </li>    
    `.trim());
    
    return `<ul>${content.join('')}</ul>`;
  }
  registerPlugins(...plugins){
    plugins.forEach(plugin => {
      const pluginContainer = document.createElement('div');
      pluginContainer.className = '.slider-list__plugin';
      pluginContainer.innerHTML = plugin.render(this.options.images);
      this.container.appendChild(pluginContainer);
      
      plugin.action(this);
    });
  }
  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';
    }
    let item = this.items[idx];
    if(item){
      item.className = 'slider-list__item--selected';
    }
    
    const detail = {index: idx}
    const event = new CustomEvent('slide', {bubbles:true, detail})
    this.container.dispatchEvent(event)
  }
  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);  
  }
  addEventListener(type, handler){
    this.container.addEventListener(type, handler);
  }
  start(){
    this.stop();
    this._timer = setInterval(()=>this.slideNext(), this.cycle);
  }
  stop(){
    clearInterval(this._timer);
  }
}

const pluginController = {
  render(images){
    return `
      <div class="slide-list__control">
        ${images.map((image, i) => `
            <span class="slide-list__control-buttons${i===0?'--selected':''}"></span>
         `).join('')}
      </div>    
    `.trim();
  },
  action(slider){
    const controller = slider.container.querySelector('.slide-list__control');
    
    if(controller){
      const buttons = controller.querySelectorAll('.slide-list__control-buttons, .slide-list__control-buttons--selected');
      controller.addEventListener('mouseover', evt => {
        const idx = Array.from(buttons).indexOf(evt.target);
        if(idx >= 0){
          slider.slideTo(idx);
          slider.stop();
        }
      });

      controller.addEventListener('mouseout', evt => {
        slider.start();
      });

      slider.addEventListener('slide', evt => {
        const idx = evt.detail.index
        const selected = controller.querySelector('.slide-list__control-buttons--selected');
        if(selected) selected.className = 'slide-list__control-buttons';
        buttons[idx].className = 'slide-list__control-buttons--selected';
      });
    }    
  }
};

const pluginPrevious = {
  render(){
    return `<a class="slide-list__previous"></a>`;
  },
  action(slider){
    const previous = slider.container.querySelector('.slide-list__previous');
    if(previous){
      previous.addEventListener('click', evt => {
        slider.stop();
        slider.slidePrevious();
        slider.start();
        evt.preventDefault();
      });
    }  
  }
};

const pluginNext = {
  render(){
    return `<a class="slide-list__next"></a>`;
  },
  action(slider){
    const previous = slider.container.querySelector('.slide-list__next');
    if(previous){
      previous.addEventListener('click', evt => {
        slider.stop();
        slider.slideNext();
        slider.start();
        evt.preventDefault();
      });
    }  
  }
};

const slider = new Slider('my-slider', {images: ['https://p5.ssl.qhimg.com/t0119c74624763dd070.png',
     'https://p4.ssl.qhimg.com/t01adbe3351db853eb3.jpg',
     'https://p2.ssl.qhimg.com/t01645cd5ba0c3b60cb.jpg',
     'https://p4.ssl.qhimg.com/t01331ac159b58f5478.jpg'], cycle:3000});

slider.registerPlugins(pluginController, pluginPrevious, pluginNext);
slider.start();

优化3：组件模型抽象
[图片上传失败...(image-b21c0a-1586444695444)]

class Component{
  constructor(id, opts = {name, data:[]}){
    this.container = document.getElementById(id);
    this.options = opts;
    this.container.innerHTML = this.render(opts.data);
  }
  registerPlugins(...plugins){
    plugins.forEach(plugin => {
      const pluginContainer = document.createElement('div');
      pluginContainer.className = `.${name}__plugin`;
      pluginContainer.innerHTML = plugin.render(this.options.data);
      this.container.appendChild(pluginContainer);
      
      plugin.action(this);
    });
  }
  render(data) {
    /* abstract */
    return ''
  }
}

class Slider extends Component{
  constructor(id, opts = {name: 'slider-list', data:[], cycle: 3000}){
    super(id, opts);
    this.items = this.container.querySelectorAll('.slider-list__item, .slider-list__item--selected');
    this.cycle = opts.cycle || 3000;
    this.slideTo(0);
  }
  render(data){
    const content = data.map(image => `
      <li class="slider-list__item">
        <img src="${image}"/>
      </li>    
    `.trim());
    
    return `<ul>${content.join('')}</ul>`;
  }
  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';
    }

    const detail = {index: idx}
    const event = new CustomEvent('slide', {bubbles:true, detail})
    this.container.dispatchEvent(event)
  }
  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);  
  }
  addEventListener(type, handler){
    this.container.addEventListener(type, handler);
  }
  start(){
    this.stop();
    this._timer = setInterval(()=>this.slideNext(), this.cycle);
  }
  stop(){
    clearInterval(this._timer);
  }
}

const pluginController = {
  render(images){
    return `
      <div class="slide-list__control">
        ${images.map((image, i) => `
            <span class="slide-list__control-buttons${i===0?'--selected':''}"></span>
         `).join('')}
      </div>    
    `.trim();
  },
  action(slider){
    let controller = slider.container.querySelector('.slide-list__control');
    
    if(controller){
      let buttons = controller.querySelectorAll('.slide-list__control-buttons, .slide-list__control-buttons--selected');
      controller.addEventListener('mouseover', evt=>{
        var idx = Array.from(buttons).indexOf(evt.target);
        if(idx >= 0){
          slider.slideTo(idx);
          slider.stop();
        }
      });

      controller.addEventListener('mouseout', evt=>{
        slider.start();
      });

      slider.addEventListener('slide', evt => {
        const idx = evt.detail.index;
        let selected = controller.querySelector('.slide-list__control-buttons--selected');
        if(selected) selected.className = 'slide-list__control-buttons';
        buttons[idx].className = 'slide-list__control-buttons--selected';
      });
    }    
  }
};

const pluginPrevious = {
  render(){
    return `<a class="slide-list__previous"></a>`;
  },
  action(slider){
    let previous = slider.container.querySelector('.slide-list__previous');
    if(previous){
      previous.addEventListener('click', evt => {
        slider.stop();
        slider.slidePrevious();
        slider.start();
        evt.preventDefault();
      });
    }  
  }
};

const pluginNext = {
  render(){
    return `<a class="slide-list__next"></a>`;
  },
  action(slider){
    let previous = slider.container.querySelector('.slide-list__next');
    if(previous){
      previous.addEventListener('click', evt => {
        slider.stop();
        slider.slideNext();
        slider.start();
        evt.preventDefault();
      });
    }  
  }
};

const slider = new Slider('my-slider', {name: 'slide-list', data: ['https://p5.ssl.qhimg.com/t0119c74624763dd070.png',
     'https://p4.ssl.qhimg.com/t01adbe3351db853eb3.jpg',
     'https://p2.ssl.qhimg.com/t01645cd5ba0c3b60cb.jpg',
     'https://p4.ssl.qhimg.com/t01331ac159b58f5478.jpg'], cycle:3000});

slider.registerPlugins(pluginController, pluginPrevious, pluginNext);
slider.start();

第三节：局部细节控制

实例一

block.onclick = function(evt){
  console.log('hide');
  evt.target.className = 'hide';
  setTimeout(function(){
    document.body.removeChild(block);
  }, 2000);
};
执行多次有问题

//如何进行统一的抽象
block.onclick = function(evt){
  block.onclick = null;
  console.log('hide');
  evt.target.className = 'hide';
  setTimeout(function(){
    document.body.removeChild(block);
  }, 2000);
};

//获取异步请求
const api = 'https://test.h5jun.com/index/gaobai?text=';
submitBtn.onclick = async function(evt){
  evt.preventDefault();
 
  let {data} = await axios.get(api + t.value);
  gaobai.src = 'data:image/jpeg;base64,' + data.data;
  console.log('data:image/jpeg;base64,' + data.data)
}

function once(fn){
  return function(...args){
    if(fn){
      let ret = fn.apply(this, args);
      fn = null;
      return ret;
    }
  }
}

function foo(idx){
  console.log(`I'm called:${idx}`);
}

foo(0);
foo(1);
foo(2);

foo = once(foo);

foo(3);
foo(4);
foo(5);

节流：

function throttle(fn, time = 500){
  let timer;
  return function(...args){
    if(timer == null){
      fn.apply(this,  args);
      timer = setTimeout(() => {
        timer = null;
      }, time)
    }
  }
}

btn.onclick = throttle(function(e){
  circle.innerHTML = parseInt(circle.innerHTML) + 1;
  circle.className = 'fade';
  setTimeout(() => circle.className = '', 250);
});

防抖debounce:

function debounce(fn){
  let timer = null
  return function(...args){
    if(timer != null) {
      clearTimeout(timer)
    }
    timer = setTimeout(() => {
      fn.apply(this, args)
      timer = null
    }, 300)
  }
}

const api = 'https://test.h5jun.com/index/gaobai?text=';

submitBtn.onclick = debounce(async function(evt){
  evt.preventDefault();
  
  let {data} = await axios.get(api + t.value);
  gaobai.src = 'data:image/jpeg;base64,' + data.data;
  console.log('data:image/jpeg;base64,' + data.data)
})

消费者模式(把数据压缩到一起，再异步执行)

function consumer(fn, time){
  let tasks = [],
      timer;
  
  return function(...args){
    tasks.push(fn.bind(this, ...args));
    if(timer == null){
      timer = setInterval(() => {
        tasks.shift().call(this)
        if(tasks.length <= 0){
          clearInterval(timer);
          timer = null;
        }
      }, time)
    }
  }
}

function add(x, y){
  let sum = x + y;
  console.log(sum);
  return sum;
}

let consumerAdd = consumer(add, 1000);

let sum = 0;
for(let i = 0; i < 10; i++){
  consumerAdd(sum, i);
}

程序语言里面：

指令式，面向过程，面向对象
声明式，逻辑的函数式的

js是指令式编程但有函数式特点
reduce方法

function add(x, y){

addMany 通用度不高

function add(x, y){
  return x + y;
}

function sub(x, y){
  return x - y;
}

function addMany(...args){
  return args.reduce(add);
}

function subMany(...args){
  return args.reduce(sub);
}

console.log(addMany(1,2,3,4));
console.log(subMany(1,2,3,4));

iterative方法高阶函数封装其他操作

function iterative(fn){
  return function(...args){
    return args.reduce(fn.bind(this));
  }
}

const add = iterative((x, y) => x + y);
const sub = iterative((x, y) => x - y);

console.log(add(1,2,3,4));
console.log(sub(1,2,3,4));

高阶函数：

自身输入是个函数或返回函数

点击实例

不通用

例：

switcher.onclick = function(evt){
  if(evt.target.className === 'on'){
    evt.target.className = 'off';
  }else{
    evt.target.className = 'on';
  }
}

1.提供一个toggl函数

function toggle(...actions){
  return function(...args){
    let action = actions.shift();
    actions.push(action);
    return action.apply(this, args);
  }
}

switcher.onclick = toggle(
  evt => evt.target.className = 'off',
  evt => evt.target.className = 'on'
);

方便扩展，直接增加状态就可以

不需要修改逻辑

function toggle(...actions){
  return function(...args){
    let action = actions.shift();
    actions.push(action);
    return action.apply(this, args);
  }
}

switcher.onclick = toggle(
evt => evt.target.className = 'warn',
  evt => evt.target.className = 'off',
evt => evt.target.className = 'on'
);

2.把loop过程抽象出来

function * loop(list, max = Infinity){
  let i = 0;
  
  //noprotect
  while(i < max){
    yield list[i++ % list.length];
  }
}


function toggle(...actions){
  let action = loop(actions);
  return function(...args){
    return action.next().value.apply(this, args);
  }
}

switcher.onclick = toggle(
  evt => evt.target.className = 'warn',
  evt => evt.target.className = 'off',
  evt => evt.target.className = 'on'
);

总结 :

各司其职：JavaScript 尽量只做状态管理
结构、API、控制流分离设计 UI 组件
插件和模板化，并抽象出组件模型
运用过程抽象的技巧来抽象并优化局部 API

第六届360前端星计划_JavaScript 从入门到放弃

主讲人

各司其职

复杂 UI 组件的设计

第三节：局部细节控制

高阶函数：

总结 :

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