From viewing the source:
div id="customfield_10901-val" class="value type-textfield" data-fieldtype="textfield" data-fieldtypecompletekey="com.atlassian.jira.plugin.system.customfieldtypes:textfield">
servername
</div>
its possible to the the field value out - for example in a button:
<script language=javascript>
alert(AJS.$("#customfield_10901-val").text().trim());
</script>