If you’re using jQuery then use this:
$('#sensor').change(function() {
$('#sensorText').val( $(this).find('option:selected').data('foo') )
})
$('#sensor').change(function() {
$('#sensorText').val( $(this).find('option:selected').data('foo') )
})
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<form id="example" name="example">
<select id="sensor">
<option value="Jval" data-foo="Jfoo">Joption</option>
<option value="Kval" data-foo="Kfoo">Koption</option>
</select>
<br />
<input type="text" value="" id="sensorText" />
</form>
1
solved Populate an input with the contents of a custom option (data-) attribute