要完成这个效果，组合使用三个事件就可以了 mousedown mousemove mouseup

在鼠标移动的时候时刻获取鼠标的坐标

效果预览

html

<p class="drag-wrap" id="drag-wrap"></p>

css

body{
  background-color: #000;
}

.drag-wrap{
  width: 600px;
  height: 500px;
  margin: auto;
  background-color: #fff;
  position: relative;
  overflow: hidden;
}

.green-dot{
  width: 2px;
  height: 2px;
  border-radius: 100%;
  background-color: green;
  position: absolute;
}

js

var app = {
  init: function () {
    var oDragWrap = document.getElementById('drag-wrap');

    this.drag(oDragWrap);
  },
  cp: function (tagName, iClass) {
    var tag = document.createElement(tagName);

    tag.className = iClass ? iClass : '';

    return tag;
  },
  css: function (ele, styleObj) {
    for(var attr in styleObj){
      ele['style'][attr] = styleObj[attr];
    }
  },
  drag: function (obj) {
    var _this = this;
    var oDragWrap = document.getElementById('drag-wrap');
    var disX,disY,p;

    obj.onmousedown = function (ev) {
      var ev = ev || event;
      disX = this.offsetLeft;
      disY = this.offsetTop;

      document.onmousemove = function (ev) {
        var ev = ev || event;
        p = _this.cp('p', 'green-dot');

        _this.css(p, {
          left: ev.clientX - disX + 'px',
          top: ev.clientY  - disY + 'px'
        });

        oDragWrap.appendChild(p);
      }

      document.onmouseup = function () {
        this.onmousemove = this.onmouseup = null;
      }

      return false;
    }
  }
}

app.init();

各位道友给点思路

http://www.cnblogs.com/lgmcolin/archive/2013/02/16/2913268.html

canvas画图板。

jquery mousemove 事件

• $(document).mousemove(function(e){ })

javascript onmousemove 事件

取得当前鼠标的位置，就在click/mousemove等事件中的event对象中！
例如你绑定了一个mousemove对象，那么

elem.onmousemove(ev) {
    // 鼠标x,y坐标
    var pX = ev.clientX,
        pY = ev.clientY;
}

你还可以直接将event对象直接log出来，看看里面到底有哪些属性

console.log(ev);