<body id="bodys">
<span id="eraser">
清除所有
</span>
<span id="colorbtn">
筆畫顏色
</span>
<input type="range" name="ram" id="ram" min="1" max="20" step="1" value="10"/>
<label id="ramnum">字體大小:10px</label>
<ul id="colorpanel">
<li>黑色</li>
<li>紅色</li>
<li>綠色</li>
<li>藍色</li>
</ul>
</body>

CSS：

*{
margin: 0;
padding: 0;
 }
.box_black{
background-color: black;
position: absolute;
}
.box_red{
background-color: red;
position: absolute;
}
.box_green{
background-color: green;
position: absolute;
}
.box_blue{
background-color: blue;
position: absolute;
}
#eraser{
width: 80px;
height: 50px;
background-color: brown;
display: inline-block;
text-align: center;
line-height: 50px;
cursor: pointer;
}
#colorbtn{
width: 80px;
height: 50px;
background-color: tomato;
display: inline-block;
text-align: center;
line-height: 50px;
cursor: pointer;
}
#colorpanel{
width: 80px;
height: 200px;
list-style: none;
margin-left: 88px;
display: none;
}
#colorpanel>li{
width: 80px;
height: 50px;
text-align: center;
line-height: 50px;
background-color: aquamarine;
display: inline-block;
cursor: pointer;
}
#colorpanel>li:hover{
background-color: orange;
}

javascript：

window.onload=function(){

  //把類名存成一個數(shù)組
 var classname=["box_black","box_red","box_green","box_blue"];
 //默認類名為box_black
 var clsname=classname[0];
 var oBody=document.getElementById("bodys");
 var oDiv=oBody.getElementsByTagName("div");
 var eraser=document.getElementById("eraser");
 var colorbtn=document.getElementById("colorbtn");
 var colorpanel=document.getElementById("colorpanel");
 var ram=document.getElementById("ram");
 var ramnum=document.getElementById("ramnum");
  colorbtn.onmouseover=function(){
  colorpanel.style.display="block";
  }
  colorbtn.onmouseout=function(){
  colorpanel.style.display="none";
  }
  colorpanel.onmouseover=function(){
  this.style.display="block";
  }
  colorpanel.onmouseout=function(){
  this.style.display="none";
  }
  for(var i=0;i<colorpanel.children.length;i++){
  colorpanel.children[i].index=i;
  colorpanel.children[i].onclick=function(){
  //鼠標點擊li切換類名來改變樣式
  clsname=classname[this.index];
  colorpanel.style.display="none";
  }
  }
  //定義默認字體大小為10px
  var WIDTH="10px";
  var HEIGHT="10px";
  //通過滑動range來改變字體大小
  ram.onmousemove=function(){
  WIDTH=HEIGHT=ram.value+"px";
  ramnum.innerHTML="字體大小:"+WIDTH;
  }
  //鼠標點擊屏幕，通過滑動鼠標不停創(chuàng)建div屬性節(jié)點，并且給它設(shè)置樣式
document.onmousedown=function(){
 document.onmousemove=function(event){
 var oevent=event||window.event;
 var scrolltop=document.documentElement.scrollTop||document.body.scrollTop;
 var scrollleft=document.documentElement.scrollLeft||document.body.scrollLeft;
 var box=document.createElement("div");
  box.className=clsname;
  box.style.width=WIDTH;
  box.style.height=HEIGHT;
  oBody.appendChild(box);
  box.style.left=scrollleft+oevent.clientX+"px";
  box.style.top=scrolltop+oevent.clientY+"px";
}
}
//當鼠標按鍵松開，注銷鼠標滑動事件
document.onmouseup=function(){
document.onmousemove=null;
}
//當橡皮差按鈕被點擊，遍歷所有div并且把它們一一從父節(jié)點里面移除
eraser.onclick=function(){
var oDiv=oBody.getElementsByTagName("div");
for(var i=0;i<oDiv.length;i++){
oBody.removeChild(oDiv[i]);
}
}
//以下為取消按鈕的冒泡事件，因為我們點擊按鈕是不能繪制div的
eraser.onmousedown=function(event){
var ievent=event||window.event;
ievent.cancelBubble=true;
}
colorbtn.onmousedown=function(event){
var ievent=event||window.event;
ievent.cancelBubble=true;
}
colorpanel.onmousedown=function(event){
var ievent=event||window.event;
ievent.cancelBubble=true;
}
ram.onmousedown=function(event){
var ievent=event||window.event;
ievent.cancelBubble=true;
}
}

}

這是基于javascript的事件基礎(chǔ)寫的，比較簡易，其實還可以進一步進行優(yōu)化。下面來看效果圖。