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  1. #1
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    TypeError: document.getelementbyid(...) is null

    Code:
    <html>
    
    	<head>
    		<title>Port Scanner for Mozilla Firefox</title>
    	</head>
    	
    	<body>
    
    		<form name="my_form" id="my_form" method="post" action="#" onsubmit="return displayMessage();">
    			<p align="center">URL/Domain Name/IP Address: <input type="text" size="20" name="uri" value="" placeholder="http://www.google.com" required/></p>
    			<table align="center" border="1" width=100% bgcolor="#f4fff0" bordercolor="green" cellspacing="2" cellpadding="2">
    				<tr>
    					<td align="center">
    						Start port: <input type="text" size="5" name="start_port" maxlength="5">
    						End port: <input type="text" size="5" name="end_port" maxlength="5"><br>
    						<input type="submit" value="Scan all ports" name="scan_all"><br>
    						<input type="submit" value="Scan only open ports" name="scan_open">						
    					</td>
    				
    				</tr>
    				<tr>
    					<td align="center">
    						<input type="text" size="20" name="scan_tcp"><br>
    						<font color="#b1b1b1">Enter port numbers separated by space. (e.g. 21 25 80)</font><br>
    						<input type="submit" value="Scan TCP ports" name="scan_tcp_ports">					
    					</td>
    				</tr>
    				<tr>
    					<td align="center">
    						<input type="submit" value="Scan common service ports" name="scan_common_tcp"><br>
    						<input type="submit" value="Scan common Trojan ports" name="scan_common_trojan_tcp">					
    					</td>
    				</tr>
    			</table>
    		</form>
    	    <script type="text/javascript">
    			function displayMessage()
    			{
    					if(document.my_form.uri.value==0)
    					{
    						document.write("<font color='red'><i>Please enter URL/Domain Name/IP Address.</i></font>");
    						return false;
    					}
    					document.write("<DIV id='loading'><BR><BR><font color='#FF6600'><i>Please wait... The ports are being scanned...</i></font></DIV>");
    					document.getElementById("my_form").submit();					
    			}
    		    window.onload=function()
    			{  
    				document.getElementById("loading").style.display="none";  
    		    }  
    		</script>
    	</body>
    </html>
    I want to submit above form. But it shows me JavaScript error in Console that
    "TypeError: document.getelementbyid(...) is null"
    This error is for code :
    document.getElementById("my_form").submit();

    I am using Firefox 24.0 and Windows 7. I have installed only 1 add-on. That is 'Firebug 1.12.3'.
    This code works fine for other browsers Except Firefox.
    Please help me to solve this problem.
    Last edited by VIPStephan; 10-13-2013 at 11:49 AM. Reason: added code BB tags

  • #2
    Regular Coder
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    You are calling document.write in the line before. Since this happens after the site has finished loading, it overwrites the entire page, so the form is just gone and hence document.getElementById() won't find it.

    The only correct answer here is: Do not ever use document.write. It is almost always a bad idea to use it. Use DOM methods instead.

  • Users who have thanked Airblader for this post:

    AbhijeetM (10-13-2013)

  • #3
    New to the CF scene
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    Thank you very much for help.
    I could solve this error by using 'innerHTML'.


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