Use setRequired to make the field required, recommended, optional using Javascript in MSCRM/CE
Scenario We have a requirement of “mobile phone” field as recommended, “email” field as required and “last name” field as optional whenever the value of “Topic” field changes on Lead Entity. On change of Topic field, JavaScript will execute and make the “mobile phone” field as recommended, “email” field as required and “last name” field as optional. JavaScript (Event Handler) will be added on Lead entity. and On Change Event of Topic of lead. So, JavaScript function will trigger on change of Topic field.
Read More

