SO - 19806174

HTML

<input type="text" name="textField" />
<textarea rows="4" cols="30"></textarea>
<input type="submit" value="next" />

JavaScript

// Cache the elements first
var $text = $('input[type="text"]');
var $textarea = $('textarea');
var $submit = $('input[type="submit"]');

// Set the onkeyup events
$submit.prop('disabled', true);
$text.on('keyup', checkStatus);
$textarea .on('keyup', checkStatus);

// Set the event handler
function checkStatus() {
    var status = ($.trim($text.val()) === '' || $.trim($textarea.val()) === '');
    $submit.prop('disabled', status);
}