简单实现JavaScript弹幕效果

 <div id="box" class="box"></div>
 <input type="text" id="txt" />
 <button onclick="send()">提交内容</button>

 function $(str) {
 return document.getElementById(str);
 }
 function send() {
 var word = $('txt').value;
 var span = document.createElement('span');
 var top = parseInt(Math.random() * 500) - 20;
 var color1 = parseInt(Math.random() * 256);
 var color2 = parseInt(Math.random() * 256);
 var color3 = parseInt(Math.random() * 256);
 var color = "rgb(" + color1 + "," + color2 + "," + color3 + ")";
 top = top < 0 ? 0 : top;
 span.style.position = 'absolute';
 span.style.top = top + "px";
 span.style.color = color;
 span.style.left = '500px';
 span.style.whiteSpace = 'nowrap';
 var nub = (Math.random() * 10) + 1;
 span.setAttribute('speed', nub);
 span.speed = nub;
 span.innerHTML = word;
 $('box').appendChild(span);
 $('txt').value = "";
 }
 setInterval(move, 200);
 function move() {
 var spanArray = $('box').children;
 for (var i = 0; i < spanArray.length; i++) {
  spanArray[i].style.left =
  parseInt(spanArray[i].style.left) - spanArray[i].speed + 'px';
 }
 }

 var color1 = parseInt(Math.random() * 256);
 var color2 = parseInt(Math.random() * 256);
 var color3 = parseInt(Math.random() * 256);
 var color = "rgb(" + color1 + "," + color2 + "," + color3 + ")";
 span.style.color = color;

var top = parseInt(Math.random() * 500) - 20;
top = top < 0 ? 0 : top;
span.style.top = top + "px";

 span.style.left = '500px';
 setInterval(move, 200);
 function move() {
 var spanArray = $('box').children;
 for (var i = 0; i < spanArray.length; i++) {
  spanArray[i].style.left =
  parseInt(spanArray[i].style.left) - spanArray[i].speed + 'px';
 }
 }