手写一个简洁且高性能的轮播图组件

如何用最低的性能，运行一个轮播图呢? js控制position:absolute 或者transform:translate，之前也这样写过。

不过有一次看过一个文章，不用js就可以写一个轮播图，原理是利用锚点控制滚动+css属性 -webkit-overflow-scrolling: touch;、scroll-snap-align: start，这样的思路真的很厉害，简单方便，性能也很高。

但是在自己的项目中却无法使用，因为用到了锚点，angular会把他当作路由，导航到404页面。

于是我想改动一下，利用js来控制滚动。这样也简单很多，不用再使用插件了。 直接剪贴代码啦，有兴趣的可以参照一下

html

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<div class="slide-nav">
  <button class="prev btn" (click)="scrollPage($event, 'l')"><span nz-icon [nzType]="btnType[xy][0]" nzTheme="outline"></span></button>
  <button class="next btn" (click)="scrollPage($event, 'r')"><span nz-icon [nzType]="btnType[xy][1]" nzTheme="outline"></span></button>
</div>
<div class="slides" [style]="style[xy]">
  <div class="slide-item" [style]="itemStyle[xy]">
    1
  </div>
  <div class="slide-item" [style]="itemStyle[xy]">
    2
  </div>
  <div class="slide-item" [style]="itemStyle[xy]">
    3
  </div>
  <div class="slide-item" [style]="itemStyle[xy]">
    4
  </div>
  <div class="slide-item" [style]="itemStyle[xy]">
    5
  </div>
</div>

css

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:host {
  width: 100%;
  height: 100%;
  display: block;
  overflow: hidden;
  position: relative;
  .slides {
    width: 100%;
    height: 100%;
    display: flex;
    // overflow-x: auto;
    // flex-direction: column;
    // scroll-snap-type: x mandatory;
    scroll-behavior: smooth;
    -webkit-overflow-scrolling: touch;
    // scroll-snap-points-x: repeat(300px);
    // scroll-snap-type: mandatory;
    .slide-item {
      scroll-snap-align: start;
      flex-shrink: 0;
      width: 100%;
      height: 100%;
      // margin-right: 16px;
      border-radius: 10px;
      background: #eee;
    }
  }
  .slide-nav{
    position: absolute;
    right: 1em;
    top: 1em;
    .btn{
      width: 2em;
      height: 2em;
      background-color: rgba(0, 0, 0, 0.2);
      cursor: pointer;
      border: 0;
      margin-left: 0.25em;
      color: rgba(255,255,255,.7);
      border-radius: .25em;
    }
  }
}

js

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export class CarouselComponent implements OnInit {
  ops={
    y:{
      wh: 'height',
      scroll: 'scrollTop',
      xy: 'top'
    },
    x: {
      wh: 'width',
      scroll: 'scrollLeft',
      xy: 'left'
    }
  }
  style={
    x: {
      flexDirection: 'row',
      scrollSnapType: 'x mandatory',
      overflowX: 'auto'
    },
    y: {
      flexDirection: 'column',
      scrollSnapType: 'y mandatory',
      overflowY: 'auto'
    }
  }
  btnType={
    y:['up', 'down'],
    x:['left', 'right'],
  }
  itemStyle={
    x:{
      marginRight: '16px'
    },
    y:{
      marginBottom: '16px'
    }
  }
  @Input() xy:'x'|'y' = 'y'
  constructor() { }

  ngOnInit(): void {
  }

  scrollPage(ev:any,direction:'l'|'r'|'b'|'t', op = this.ops[this.xy]){
    let e = ev.target
    
    
    while(e && e.nodeName!=='BUTTON'){
      e=e.parentNode
    }
    let sildesDom = e.parentNode.nextElementSibling
    let sChildren = sildesDom.children
    let scrollTop = sildesDom[op.scroll]
    let index = 0
    let sum = 0
    for(let i=0,len = sChildren.length; i<len; i++){
      let rect = sChildren[i].getBoundingClientRect()
      if(scrollTop<=sum){
        index = i
        break
      }else{
        sum += rect[op.wh]+16
      }
    }
    if(index+1==sChildren.length){
      sum=0
    }else{
      if(direction=='r'||direction=='b'){
        let rect = sChildren[index+1].getBoundingClientRect()
        sum += rect[op.wh]+16
      }else if(index!==0){
        let rect = sChildren[index-1].getBoundingClientRect()
        sum-=rect[op.wh]+16 
      }
    }
    sildesDom.scroll({
      [op.xy]: sum,
    })
  }

}

通过scrollTop来判断当前在第几屏，xy传参判断横向滚动还是纵向滚动。
参考文章：CSS-Only Carousel