进度条

css

  *{
            margin: 0;
            padding: 0;
        }
        .scroll{
            margin:100px;
            width: 500px;
            height: 5px;
            background: #ccc;
            position: relative;
        }
        .bar{
            width: 10px;
            height: 20px;
            background: #369;
            position: absolute;
            top: -7px;
            left: 0;
            cursor: pointer;
        }
        .mask{
            position: absolute;
            left: 0;
            top: 0;
            background: #369;
            width: 0;
            height: 5px;
        }

<div class="scroll" id="scroll">
    <div class="bar" id="bar"></div>
    <div class="mask" id="mask"></div>
</div>
<p></p>

var scroll = document.getElementById('scroll');
    var bar = document.getElementById('bar');
    var mask = document.getElementById('mask');
    var ptxt = document.getElementsByTagName('p')[0];
    var barleft = 0;
    bar.onmousedown = function(event){
        var event = event || window.event;
        var leftVal = event.clientX - this.offsetLeft;
        var that = this;
        // 拖动一定写到 down 里面才可以
        document.onmousemove = function(event){
            var event = event || window.event;
            barleft = event.clientX - leftVal;
            if(barleft < 0)
                barleft = 0;
            else if(barleft > scroll.offsetWidth - bar.offsetWidth)
                barleft = scroll.offsetWidth - bar.offsetWidth;
            mask.style.width = barleft +'px' ;
            that.style.left = barleft + "px";
            ptxt.innerHTML = "已经走了" + parseInt(barleft/(scroll.offsetWidth-bar.offsetWidth) * 100) + "%";

            //防止选择内容&#45;&#45;当拖动鼠标过快时候，弹起鼠标，bar也会移动，修复bug
            window.getSelection ? window.getSelection().removeAllRanges() : document.selection.empty();
        }

    }
    document.onmouseup = function(){
        document.onmousemove = null; //弹起鼠标不做任何操作
    }

process.png