js弹幕案例 js观察者模式的弹幕案例

时间:2021-01-28 weixin_44646551 人气:0

观察者模式的弹幕案例

上代码

弹幕.html:

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    input{
    
      width:1208px;
      height: 38px;
      font-size: 30px;
      position: absolute;
    }
    .div0{
      width:1208px;
      height: 768px;
      position: relative;
      overflow: hidden;
    }
    video{
    width:1208px;
      height: 720px;
    }
  </style>
</head>
<body>
  <div class="div0">
    <video src="./y2mate.com - nylonjapan11_wjhIR0JdoXA_1080p.mp4" controls></video>
    <br>
   
    <input type="text">
  </div>
  <script type="module">
    import Bullet from "./observer/Bullet.js";//导入模块
    var input=document.querySelector("input");
    document.addEventListener("keyup",keyHandler);
//input的键盘监听事件按回车实例化BUllet
    function keyHandler(e){
      if(e.keyCode!==13) return;
      if(input.value.trim().length===0) return;
      var bullet=new Bullet(input.value);
      bullet.appendTo(".div0");
      input.value="";
    }
  </script>
</body>
</html>

bullet.js:

import TimeManager from "./TimeManager.js";//导入观察者

export default class Bullet {
  rect;
  x;
  speed = 2;
  width;
  constructor(txt) {
    this.elem = this.createElem(txt);
  }
  //创建弹幕
  createElem(txt) {
    if (this.elem) return this.elem;
    var div = document.createElement("div");
    Object.assign(div.style, {
      whiteSpace: "nowrap",
      position: "absolute",
    })
    div.textContent = txt
    return div;
  }
  //将弹幕随机位置插入视屏中并且将弹幕插入到观察者中的list数组中
  appendTo(parent) {
    if (typeof parent === "string") parent = document.querySelector(parent);
    parent.appendChild(this.elem);
    this.rect = parent.getBoundingClientRect();
    Object.assign(this.elem.style, {
      top: Math.random() * this.rect.height / 4 + "px",
      left: this.rect.width + "px"
    });
    this.x = this.rect.width;
    this.width = this.elem.offsetWidth;
    TimeManager.instance.add(this);
  }
  //使弹幕移动，并给限制如果弹幕移出视频，则在list中删除此元素
  update() {
    if (!this.width) return;
    this.x -= this.speed;
    this.elem.style.left = this.x + "px";
    if (this.x < -this.width) {
      TimeManager.instance.remove(this);
      this.elem.remove();
      this.elem = null;
    }
  }
}

TimeManager.js:

export default class TimeManager {
  static _instance
  list = new set()//设置一个set类型的变量
  ids
  constructor() {

  }
  static get instance() {
    //设置一个静态方法，此为单例模式，
    if (!TimeManager._instance) {
      Object.defineProperty(TimeManager, '_instance', {
        value: new TimeManager()
      })//给TimeManager设置属性如果没有则赋值为实例并保存，有则直接给保存的实例
    }
    return TimeManager._instance;
  }
  //将带入的变量加入到list中如果list中有元素时则没16ms调用updata方法
  add(elem) {
    this.list.add(elem)
    if (this.list.size > 0 && !this.ids) {
      this.ids = setInterval(() => this.updata(), 16)
    }
  }
  //将带入的变量从list中删除，如果list中没有变量了就将定时器关闭，销毁定时器
  remove(elem) {
    this.list.delete(elem)
    if (this.list.size === 0 && this.ids) {
      clearInterval(this.ids)
      this.ids = undefined
    }
  }
  //遍历所有list里的元素，如果元素带有updata方法，则调用updata方法
  updata() {
    this.list.forEach(item => {
      if (item.updata) item.updata
    })
  }
}

加载全部内容