I am trying to open a window, with a url, and parameter from array form field. Here is the code:

<input type="text" name="parameter[1]" value="1223344"><input type="button" value="Check ID" onclick="window.open('http://www.website.com/profile.php?sid=&MemberID=' + document.MainForm.parameter[1].value)">

I am getting that document.MainForm.parameter.1 is null or not an object.

How can I properly make javascript recorgenize the field?