We can use JavaScript to validate the content of a form before submitting it to a CGI web server.
For example:
We can't check that an email address is genuine, but we can check that it appears to be genuine, by:
// JavaScript function checkEmail(id) { var email = document.getElementById(id).value; // alert(email); var atPos = email.indexOf("@"); var dotPos = email.lastIndexOf("."); if((atPos < 1) || // It contains an @ and not as the first character (dotPos < atPos+2) || // Check there is a dot at least 2 chars after the @ (dotPos > email.length-2)) // Check the dot isn't the last character { alert("EMail address is invalid"); return false; } return true; } <!-- The HTML --> <form type='get' action='#' onsubmit="return checkEmail('email')"> <p>Email: <input type='text' size='40' name='email' id='email' /></p> <p><input type='submit' value='Submit' /></p> </form>
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We simply extract the sequence remove white space and line breaks and see how many characters are left.
// JavaScript function checkSequence(id, minLen) { var sequence = document.getElementById(id).value; // alert(sequence); sequence = sequence.replace(/\s/g,""); // alert(sequence); if(sequence.length < minLen) { var msg = "Your sequence must contain at least " + minLen + " residues"; alert(msg); return false; } return true; } <!-- The HTML --> <form type='get' action='#' onsubmit="return checkSequence('seq', 20)"> <p>Sequence:<br /> <textarea cols='60' rows='5' name='seq' id='seq' /></textarea> <p><input type='submit' value='Submit' /></p> </form>
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