Remove the inline javascript:
<script>
var button = document.findElementById('login-button');
button.addEventListener('onmouseover', function(event) { hover(event.target, 1) });
button.addEventListener('onmouseout', function(event) { hover(event.target, 0) });
</script>
<input type="submit" class="button" value="Enter" name="feature=111" id="login-button">
or use the css :hover pseudoselector if it the hover() function is just for styling.