It is possible to use custom JavaScript in embedded forms.

Custom JavaScript can be added to a form by using a <script> tag and adding the cam-scriptdirective:

<form role="form">
  <script cam-script type="text/form-script">
  // custom script goes here
  </script>
</form>

原文: https://docs.camunda.org/manual/7.9/reference/embedded-forms/javascript/cam-script/