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

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openin...@gmail.com

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Oct 13, 2013, 5:40:55 AM10/13/13
to khan-academy-javas...@googlegroups.com
<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.

Larry Serflaten

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Oct 13, 2013, 7:11:17 AM10/13/13
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This group is for Q&A at the Khan Academy Computer Science JavaScript section.  There is no HTML used (by the students) at that site. You may find better response if you ask your question in an HTML or other JavaScript group.   

ling...@gmail.com

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Feb 10, 2020, 1:56:16 AM2/10/20
to Khan Academy Javascript Technical Q&A
This error TypeError: document.getelementbyid(...) is null would seem to indicate that there is no such element with an ID passed to getElementById() exist. This can happen if the JavaScript code is executed before the page is fully loaded, so its not able to find the element. The solution is that you need to put your JavaScript code after the closure of the HTML element or more generally before < /body > tag.

openin...@gmail.com

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Feb 11, 2020, 5:16:02 AM2/11/20
to Khan Academy Javascript Technical Q&A
Got it. Thank you.
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