實戰練習1：使用原生js實現簡單的視頻彈幕效果。

項目描述（需求分析）：javascript

一、使用html5中的video標籤，建立一個視頻播放器；css

二、視頻屏幕下能夠輸入彈幕，開頭不能是空格，且能夠經過提交按鈕或者enter鍵進行提交；html

三、輸入的彈幕在視頻區域實現從左到右滑動，字體顏色隨機，大小隨機，速度隨機，超出區域則不能顯示；html5

html部分：java

<!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">
    <link rel="stylesheet" href="css/index.css">
    <title>彈幕效果</title>
</head>
<body>
    <div class="main">
        <div class="container">
            <div class="movie">
                <video src="./video/laopo.mp4" controls="controls"></video>
            </div>
            <div class="danmu">
                <input type="text" class="input" placeholder="請輸入彈幕" >
                <div id="btn">發送彈幕</div>
            </div>
            <div class="al">
                輸入內容不能爲空!
            </div>
        </div>
    </div>
    <script src="js/index.js"></script>
</body>
</html>

css部分：app

body{
    margin: 0;
    padding: 0;
    list-style: none;
}
body{
    font-family: sans-serif,'Microsoft Yahei'
}
.main{
    position: relative;
    margin: 100px auto;
    width: 1024px;
    height: 612px;
    background: url("../img/bg.jpg") no-repeat;
}
.container{
    position: absolute;
    top: 88px;
    left: 186px;
    width: 652px;
    height: 408px;
    background:black;
    overflow: hidden;
}
.movie video{
    position: relative;
    width: 652px;
    height: auto;
}
.movie span{
    position: absolute;
    white-space: nowrap;
    /* left: 100px; */
    /* top: 50px; */
    /* font-size: 20px; */
    /* color: red; */
}
.danmu{
    position: relative;
    margin: 0 auto;
    overflow: hidden;
    width: 500px;
    height: 25px;
    border-radius: 5px;
}
.danmu .input{
    margin: 0;
    padding: 0;
    outline: none;
    border: 0;
    width: 420px;
    height: 25px;
    text-indent: 8px;
}
#btn{
    text-align: center;
    position: absolute;
    letter-spacing: 1px;
    top: 0;
    right: 0;
    height: 25px;
    width: 80px;
    font-size: 14px;
    line-height: 25px;
    color: white;
    background: #ff6700;
    cursor: pointer;
}
.al{
    position: absolute;
    bottom: 80px;
    margin-left: -90px;
    left: 50%;
    width: 180px;
    height: 24px;
    color: white;
    font-size: 14px;
    line-height: 24px;
    text-align: center;
    letter-spacing: 1px;
    display: none;
    border-radius: 8px;
    background: orangered;
    box-shadow: 2px 2px 5px rgba(0,0,0,0.5);
}

js部分：dom

var oMovie=document.getElementsByClassName('movie')[0],
    oInput=document.getElementsByClassName('input')[0],
    oBtn=document.getElementById('btn'),
    oAl=document.getElementsByClassName('al')[0];
    oMovieWidth=oMovie.offsetWidth;
var timer2;

oBtn.onclick=send;
oInput.onkeydown=function(e){
    if(e.keyCode==13){
        send();
    }
}
function send(){
    if(oInput.value.length<=0 || (/^\s+$/).test(oInput.value)){
        oAl.style.display='block';
        timer2=setTimeout(function(){
        oAl.style.display='none';
        },1500)
        return;
    }
     createSpan(oInput.value);
     oInput.value="";
}

function createSpan(text){
    var oSpan=document.createElement('span');
    oSpan.innerText=text;
    oSpan.style.left=oMovieWidth+'px';
    oMovie.appendChild(oSpan);
    styleSpan(oSpan);
}
function styleSpan(dom){
    dom.style.top=random(0,180)+'px';
    dom.style.color='rgb('+random(0,255)+','+random(0,255)+','+random(0,255)+')';
    dom.style.fontSize=random(8,24)+'px';
    var domW=dom.offsetWidth;
    var speed = [0, 1, 2][random(0, 2)];
    dom.timer=setInterval(function(){
        switch(speed){
            case 0:
                dom.style.left=dom.offsetLeft-2+'px';
                break;
            case 1:
                dom.style.left=dom.offsetLeft-4+'px';
                break;
            case 2:
                dom.style.left=dom.offsetLeft-4+'px';
        }
        if (dom.offsetLeft <= -domW) {
            clearInterval(dom.timer);
            oMovie.removeChild(dom);
        }
    },20)
}
function random(start,end){
    return Math.floor(Math.random()*(end+1-start)+start);
}