In addition to showing and hiding fields in CRM 4.0, an additional technique many of us used was to change the requirement level of a field based on the value of another field.  Again, this was an unsupported customization but very, very common.

Setting the Requirement Level ( CRM 4.0 )

In my research, I have found several techniques to set the requirement level:

Set the .req property:

// No requirement
crmForm.all.new_field.req = 0;
crmForm.all.new_field.setAttribute("req", 0);

// Recommended
crmForm.all.new_field.req = 1;
crmForm.all.new_field.setAttribute("req", 1);

// Required
crmForm.all.new_field.req = 2;
crmForm.all.new_field.setAttribute("req", 2);

SetFieldReqLevel method

// No requirement
crmForm.SetFieldReqLevel("new_field", 0);

// Required
crmForm.SetFieldReqLevel("new_field", 1);

// Recommended
crmForm.SetFieldReqLevel("new_field", 2);

Setting the Requirement Level ( CRM 2011 )

Thanks to the new and improved CRM 2011 JavaScript object model, we can now set the requirement level like this:

Xrm.Page.getAttribute("new_field").setRequiredLevel("none");
Xrm.Page.getAttribute("new_field").setRequiredLevel("recommended");
Xrm.Page.getAttribute("new_field").setRequiredLevel("required");

Getting the Requirement Level ( CRM 4.0 )

The CRM 4.0 JavaScript object model has a built-in property on all fields that allows you to get the requirement level:

var reqLevel - crmForm.all.new_field.RequiredLevel;

Getting the Requirement Level ( CRM 2011 )

CRM 2011 gives us a corresponding method to get the requirement level of a field:

var reqLevel = Xrm.Page.getAttribute("new_field").getRequiredLevel();

It returns a string: “none”, “recommended”, or “required”

The CRM Migration Assistant converts the above CRM 4.0 JavaScript to the proper CRM 2011 equivalent which will move your code from Unsupported to Supported.