弹幕制作小练习

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>

    .container{
        width: 500px;
        height: 300px;
        background: black;
        position: relative;
    }
    span{
        font-size: 16px;
        color: white;
        /* transition: all 3s; */
        position: absolute;
        width: 500px;
        overflow: hidden;
    }

    </style>
</head>
<body>
        <div class="container">
        
        </div>    

        <div class="comment">
            <input type="text" id="sendText" placeholder="来几条弹幕吧~~">
            <button id="sendBtn">发送</button>
        </div>

<script>
    let video=document.getElementsByTagName('video');
    let container=document.getElementsByClassName('container')[0];
    //随机函数
    let random = function (start,end){
        return Math.floor(Math.random()*(end-start+1))+start;
    }
    let wordMove = function(){
        let span = document.createElement("span");
        span.innerHTML = sendText.value.substring(0,50);
        sendText.value = "";
        let speed = random(5,10);
        //span标签开始移动的水平位置
        span.style.left = container.offsetWidth + container.offsetLeft+ "px";
        console.log(span.style.left,);

        //开始移动的垂直位置
        let totalHeight = container.offsetTop + 300;
        span.style.top = random(container.offsetTop + 10, totalHeight -15) +"px";
    //    console.log(container);
       container.appendChild(span);


        let stopTimer = setInterval(function(){
            span.style.left = parseInt(span.style.left)-speed+ "px";  //50ms span移动一次
            //<0 后终止计时器 并移除span标签
            if(parseInt(span.style.left)<0){
                clearInterval(stopTimer);
                container.removeChild(span);
            }
        },50)
    }
    sendBtn.onclick = wordMove;
    document.onkeydown = function (e){
        if(e.keyCode === 13){
            wordMove();
        }
    }

</script>


</body>
</html>
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