JavaScript树形图组件源码实现：添加图片并处理错误

function alai_imagelist()
{try{
var item=[]
count=0
this.path=""
this.type="gif"
this.err=""
iml=this
//this.copywrite="Copywrite by Alai(赖国欣) (c)2003，All right reserved!"
this.add=function(src,key)
{
var img=new Image()
if(src==null || src=="")return
if(src.indexOf("/")==-1)src=iml.path+src
if(!(/\.gif$|\.jpg$|\.png$|\.bmp$/i).test(src))src+="."+iml.type
if(key==null || key=="")key=src.replace(/(.*\/){0,}([^\.]+).*/ig,"$2")
item[count]=img;img.index=count;item[key]=img;count++;
img.onerror=function()
{
alert("alai_imagelist cause run time error:\nImage file "+img.src+" not found!")
item[img.index]=null;item[key]=null;count--;
}
img.src=src
return img
}
this.item=item
this.count=function(){return count;}
}
catch(e){
iml.err="alai_imagelist cause run time error!\nError number:"+e.number+".\nError description:"+e.description;

iml.err+="\n    -- \nYou can send the case and error description message to A@lai.com.cn for support.Please visit http://www.9499.net to get the last release!"
alert(iml.err);
return iml;
}
}



function alai_tree(imageList,indent,toObject,labelStyle)
{try{
if(!document.getElementById){
throw new Error(999,"Your browser dosen't support Alai_tree(),IE5.0+ is recommended.");
}
var count=0,depth=0,nodes=[],tree=this
//this.copywrite="Copywrite by Alai(赖国欣) (c)2003，All right reserved!"
this.err=""
imageList=imageList==null?new alai_imagelist():imageList
var icons=imageList.item
this.imageList=imageList
if(icons["default"]!=null){
if(icons["link"]==null)icons["link"]=icons["default"]
}
var showExpand=icons["expand"]!=null && icons["collapse"]!=null
if(showExpand)
{ if(icons["expand_top"]==null)icons["expand_top"]=icons["expand"]
if(icons["expand_end"]==null)icons["expand_end"]=icons["expand"]
if(icons["collapse_top"]==null)icons["collapse_top"]=icons["collapse"]
if(icons["collapse_end"]==null)icons["collapse_end"]=icons["collapse"]
}
var showBranch=icons["leaf"]!=null && icons["twig"]!=null