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Javascript document.getElementById doesn't seem to work

Answer 1

+5 A:

You're calling showmsg before the whole page (and hence the display div) is loaded. Hence the error. Call it from onload and it'll work.

Add this function to the <head>

function handleLoad()
{
  document.getElementById("username").focus()
  if("WebSockets" in window){
   pass;
  }else{
    showmsg("Your browser doesn't support WebSockets. Try Google Chrome.");
  }
}

and call it from onload

<body onload="handleLoad()">

Amarghosh 2010-07-09 05:36:30

Answer 2

+1 A:

Put your script tag at the end of the document:. In your case the page has not been completely parsed into DOM tree, but your script executes anyway:

       <body onload="document.getElementById('username').focus()">
           <input type="text" id="username" />
           <div id="container">
               <div id="display"></div>
               <div id="onlineusers"></div>
               <div class="clearfix"></div>
           </div>

           <div id="container2">
               <input type="text" id="inputline" length="55" />
               <input type="button" id="sendbutton" value="Send" />
           </div>

           <script type="text/javascript">
           function showmsg(str){
               var display = document.getElementById('display');
               display.innerHTML += "<p>" + str + "</p>";
           }

           if("WebSockets" in window){
              pass;
           }else{
               showmsg("Your browser doesn't support WebSockets. Try Google Chrome.");
           }
       </script>
   </body>

This is also considered a good practice for performance reasons: http://developer.yahoo.com/performance/rules.html#js_bottom

naikus 2010-07-09 05:40:49

Answer 3

+4 A:

Move your script-section down to the bottom of the page. Otherwise it is executed before the page has been loaded.

Btw: Putting scripts at the bottom of your page is even a "best practice" and recommended by Google, Yahoo & Co

Gerhard Dinhof 2010-07-09 05:41:32

+1 for suggesting the yahoo link. I did not see it before (when i edited my answer)

naikus 2010-07-09 05:52:03

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Javascript document.getElementById doesn't seem to work

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