JS realizes video barrage effect

import TimeManager from './TimeManager.js';
 
export default class Bullet{
    
    elem;
    x;
    speedX=2;
    width;
 
    constructor(txt){
        this.elem = this.createElem(txt);
    }
    createElem(txt){
        if(this.elem) return
        let div = document.createElement("div");
        Object.assign(div.style,{
            position:"absolute",
            whiteSpace: "nowrap",
            fontSize:"16px",
            // color:"#000",
            color:"#e00",
        })
        div.textContent = txt;
        return div
    }
    appendTo(parent){
        if(typeof parent === "string") parent = document.querySelector(parent);
        parent.appendChild(this.elem);
        let rect = parent.getBoundingClientRect();
        this.elem.style.top = Math.random()*rect.height/4 + "px";
        this.width = this.elem.offsetWidth;
        this.x = rect.width;
        this.elem.style.left = this.x + "px";
        TimeManager.instance.add(this);
    }
    update(){
        if(!this.elem) return;
        this.x -= this.speedX;
        this.elem.style.left = this.x + "px";
        if(this.x<-this.width){
            this.elem.remove();
            TimeManager.instance.remove(this);
            this.elem = null;
        }
    }
}

export default class TimeManager{
    
    static _instance;
    list = new Set();
    ids;
 
    constructor(){
 
    }
    static get instance(){
        TimeManager._instance = TimeManager._instance? TimeManager._instance : new TimeManager();
        return TimeManager._instance;
    }
    add(elem){
        if(!elem) return
        if(elem.update) this.list.add(elem);
        if(!this.ids) this.ids = setInterval(()=>{
            this.update();
        },16);
    }
    remove(elem){
        if(!elem) return
        this.list.delete(elem);
        if(this.list.size===0 && this.ids){
            clearInterval(this.ids);
            this.ids=0;
        }
    }
    update(){
        this.list.forEach(item=>{
            item.update();
        })
    }
}

import Bullet from './Bullet.js';
 
export default class Player extends EventTarget{
 
    static WIDTH=638;
    static HEIGHT=493;
    elem;
    input;
 
    constructor(path){
        super();
        this.elem = this.createElem(path);
        document.addEventListener("keyup",e=>this.keyHandler(e));
    }
    keyHandler(e){
        if(e.keyCode !== 13) return;
        if(this.input.value.trim().length===0) return;
        let b = new Bullet(this.input.value);
        b.appendTo(this.elem);
        this.input.value = "";
    }
    appendTo(parent){
        if(typeof parent==="string") parent = document.querySelector(parent);
        parent.appendChild(this.elem);
    }
    createElem(path){
        // The outermost container of the player let player = document.createElement("div");
        player.className = "player";
        Object.assign(player.style,{
            width:Player.WIDTH+"px",
            height:Player.HEIGHT+"px",
            userSelect:"none",
            overflow: "hidden",
            position:"relative",
            verticalAlign:"baseline",
        })
        // Video playback part of the player: should include the top author and feedback bar, video status button, and video display part. . . .
        let videoWrap = document.createElement("div");
        Object.assign(videoWrap.style,{
            width:"100%",
            height:"447px",
            backgroundColor:"#000",
            position:"relative",
            top:0,
            display:"flex",
            flexDirection:"column",
        })
        // Create the upper layer of the player: including title, author, feedback and report, etc. . . .
        let videoTop = document.createElement("div");
        Object.assign(videoTop.style,{
            width:"100%",
            height:"42px",
            position:"relative",
            top:"0px",
            left:"0px",
            opacity:"0",
            color:"#fff",
            pointerEvents:"none",
            // transition: "all .2s ease-in-out",
            transition: "all .2s",
        })
        // Video playback status switch // let videoState = document.createElement("div");
        // Video playback part let videoContent = document.createElement("div");
        Object.assign(videoContent.style,{
            width:"100%",
            // height:"100%",
            height:"361px",
            position:"relative",
            userSelect:"none",
        })
        let video = document.createElement("video");
        video.src = path;
        video.controls = "controls";
        video.preload = "auto";
        Object.assign(video.style,{
            // Video centering: The progress bar is lengthened, but the video is not lengthened and is directly centered:
            height:"100%",
            width:"100%",
        })
        videoContent.appendChild(video);
 
        // Video playback and bullet screen scrolling control bar: clarity/speed/loop/mirror/widescreen/full screen webpage/progress bar, etc.
        let videoControlWrap = document.createElement("div");
        Object.assign(videoControlWrap.style,{
            width:"100%",
            height:"44px",
            opacity:"0",
            position:"relative",
            bottom:"0",
        })
 
        // Send bullet screen at the bottom and set the style of sending bullet screen: such as bullet screen color/font size/scroll/hover/speed/font/shield, etc. . .
        let bottomArea = document.createElement("div");
        Object.assign(bottomArea.style,{
            width:"100%",
            height:"46px",
        })
        this.input = document.createElement("input");
        Object.assign(this.input.style,{
            width:"130px",
            height:"30px",
            color:"#212121",
            // border:"0px",
            lineHeight:"30px",
            boxSizing: "border-box",
            minWidth: "115px",
            padding:"0 5px",
            fontSize:"12px",
            border:"1px solid #e7e7e7", //Frame style:
            backgroundColor:"#f4f4f4",
        })
        bottomArea.appendChild(this.input);
 
        videoWrap.appendChild(videoTop);
        videoWrap.appendChild(videoContent);
        videoWrap.appendChild(videoControlWrap);
 
        player.appendChild(videoWrap);
        player.appendChild(bottomArea);
        return player;
    }
}

<!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>
    </style>
</head>
<body>
    <script type="module">
        import Player from './js/Player.js';
        import TimeManager from './js/TimeManager.js';
        import Bullet from './js/Bullet.js';
 
        //Player usage let player = new Player("./test3.mp4");
        player.appendTo("body");
 
    </script>
</body>
</html>