js代码没有出现错误，但是网页中没有预想的效果
html

    
        
        
        
    
    
     
Snapshots
      

          

              Ballon
          
          

              Tree
          
          

              Sea
          
      
      
      
Choose an image.
      
    

js代码

window.onload = prepareGallery;
function prepareGallery(){
    if(!document.getElementsByTagName)
    {return false;}
    if(!document.getElementById)
    {return false;}
    if(!document.getElementById("imageGallery"))
    {return false;}

    var gallery = document.getElementById("imageGallery");
    var links = gallery.getElementsByTagName("a");
    for(var i = 0;i < links.length;i++){
        links[i].onclick = function(){
           return !showPic(this);
      }
    }
}
function showPic(whichpic){
    if(!document.getElementById)
    {return false;}
    var source = whichpic.getAttribute("href");
    if(!document.getElementById.getElementById("placeholder"))
    {return false;}
    var placeholder = document.getElementById("placeholder");
    if(placeholder.nodeName != "IMG")
    {return false;}
    placeholder.setAttribute("src",source);
    if(document.getElementById("description"))
    {
        if(whichpic.getAttribute("title")){
        var title = whichpic.getAttribute("title");
        }else{
            title = "";
        }
    var description = document.getElementById("description");
    if(description.firstChild.nodeType == 3){
    description.firstChild.nodeValue = title;
    }
   }
    return true;
}