Placeholder. This label appear only if the value is not set yet.
Examples
JS Config
<select id="dropdown"></select>
<script>
$('#dropdown').dropdown({ placeholder: 'Select One...', width: 200, dataSource: '/Locations/GetCountries', valueField: 'id' });
</script>
HTML Config
<input type="text" class="gj-textbox-md" placeholder="Select One..." style="width: 200px" /><br/>
<select id="dropdown" placeholder="Select One..." width="200" data-source="/Locations/GetCountries" data-value-field="id"></select>
<script>
$('#dropdown').dropdown();
</script>
Bootstrap
<input type="text" class="form-control" placeholder="Select One..." style="width: 200px" /><br/>
<select id="dropdown" placeholder="Select One..." width="200" data-source="/Locations/GetCountries" data-value-field="id"></select>
<script>
$('#dropdown').dropdown({ uiLibrary: 'bootstrap' });
</script>
Bootstrap 4
<input type="text" class="form-control" placeholder="Select One..." style="width: 200px" /><br/>
<select id="dropdown" placeholder="Select One..." width="200" data-source="/Locations/GetCountries" data-value-field="id"></select>
<script>
$('#dropdown').dropdown({ uiLibrary: 'bootstrap4' });
</script>