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

  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.

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

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