<form id="demo" action="#">

<label>Width:</label>

<input name="width" size="2">

<input type="submit" value="Run">

</form>

<script type="text/javascript">

YUI().use('node', function(Y) {

var form = Y.one('#demo'),

input = Y.one('#demo input[name=width]'),

button = Y.one('#demo input[type=submit]');

button.on('click', function(e) {

e.preventDefault(); // keep the form from submitting

var value = input.get('value'),

width = form.get('offsetWidth');

if (value == '') {

input.set('value', width);

} else {

form.set('offsetWidth', value);

}

});

});

</script>