                        課程
                    
                        /前端開發
                        
                            /JavaScript
                        
                        /搜索框制作

Uncaught TypeError: Cannot read property 'style' of null, 是什么情況？

<!DOCTYPE?html>
<html>
<head>
<meta?charset="UTF-8">
<meta?http-equiv="X-UA-Compatible"?content="IE=edge"><!--?為了兼容IE?-->
<title>js實現搜索框下拉功能</title>
<style?type="text/css">
body,?ul,?li,?div,?form,input{margin:0;?padding:0;}
body{background-color:?#333;}
.bg_div{
background-image:?url(images/river.jpg);?
width:1366px;?height:690px;
margin:0?auto;
position:?relative;
}
.logo{
background-image:?url(images/logo.png);
width:107px;?height:?53px;
float:?left;
margin-right:?15px;
margin-top:?-10px;?/*設置負值往反方向移動*/
}
form{
float:?left;?
background-color:?#fff;

}
input{
border:?0;?
outline:none;/*去掉chrome下點擊輸入框時高亮顏色*/
}
.search_input_text{
width:?350px;
height:?38px;
line-height:?38px;
float:?left;
padding:?0?5px;
}
.search_input_button{
background:?url(images/search_button.png)?center?center?no-repeat;
width:?38px;
height:?38px;
line-height:?38px;
float:?left;
cursor:?pointer;?/*光標移到按鈕時變為“小手”形狀*/
}
.search_box{
position:?absolute;
top:?200px;
left:?200px;
}
.suggest?ul{
width:?396px;
border:?1px?solid?#999;
background:?#fff;
position:?absolute;
top:?238px;
left:?322px;
}
.suggest?li{
padding:?3px;
list-style-type:?none;
line-height:?25px;
}
.suggest?li:hover{
text-decoration:?underline;
background-color:?#ccc;
cursor:?pointer;
}
</style>
</head>
<body>
<div>
<div>
<div></div>
<form??id="search_form"?>
<input?type="text"?id="search_input"?/>
<input?type="submit"?value=""?/>
</form>
</div>
<div?id="search_suggest"?style="display:?none;">
<ul?id="search_result">
<li>搜索結果1</li>
<li>搜索結果2</li>
<li>搜索結果3</li>
</ul>
</div>
</div>
<script?type="text/javascript">
//?先封裝幾個常用的函數
var?getDOM?=?function?(id)?{
return?document.getElementById('id');
};
var?addEvent?=?function?(id,?event,?fn)?{
var?el?=?getDOM(id)||document;
if(el.addEventListener){//非IE瀏覽器
el.addEventListener(event,?fn,?false);
}else?if(el.attachEvent){//IE瀏覽器
el.attachEvent('on'+event,?fn);
}
};
//?獲取輸入框的位置
var?getElementLeft?=?function(element)?{//獲取距離瀏覽器左邊的距離
var?actualLeft?=?element.offsetLeft;//獲取距離父元素左邊的距離
var?current?=?element.offsetParent;
while(current!==?null){
actualLeft?+=?current.offsetLeft;
current?=?current.offsetParent;
}
return?actualLeft;
};
var?getElementTop?=?function(element)?{//獲取距離瀏覽器頂部的距離
var?actualTop?=?element.offsetTop;
var?current?=?element.offsetParent;
while(current!==?null){
actualTop?+=?current.offsetTop;
current?=?current.offsetParent;
}
return?actualTop;
};//至此已封裝完畢

addEvent('search_input',?'keyup',?function(){
getDOM('search_suggest').style.top?=?getElementTop(getDOM('search_form'))+?38?+'px';
getDOM('search_suggest').style.left?=?getElementLeft(getDOM('search_form'))+'px';
getDOM('search_suggest').style.position?=?'absolute';
getDOM('search_suggest').style.display?=?'block';
});
</script>
</body>
</html>

自己看了半天都沒有找出來錯誤在哪里??？