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

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  1. #1
    Join Date
    Dec 2012
    Posts
    3

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

    <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.

  2. #2
    Join Date
    Mar 2007
    Location
    U.K.
    Posts
    1,127
    You cannot use document.write after the page has loaded.
    Where used, return should be executed unconditionally and always as the last statement in the function.

    That's my signature, it's not part of the damn post!

  3. #3
    Join Date
    Dec 2012
    Posts
    3
    Thank you very much. I could solve this problem by using 'innerHTML'.

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