JavaScript in MS CRM 2013/2015

Get current entity name

var entity = Xrm.Page.data.entity.getEntityName();

Disable the field

Xrm.Page.getControl("telephone1").setDisabled(true);

Hide field

Xrm.Page.getControl("telephone1").setVisible(false);

Get value from one field and set to other field

var phone = Xrm.Page.getAttribute("telephone1").getValue();

    

        Xrm.Page.getAttribute("fax").setValue(phone);

Get Current User Role

Xrm.Page.context.getUserRoles();

Hiding tab
Xrm.Page.ui.tabs.get(tabindex).setVisible(false);
or
Xrm.Page.ui.tabs.get("tabname").setVisible(false);

Showing tab
Xrm.Page.ui.tabs.get(tabindex).setVisible(true);
or

Xrm.Page.ui.tabs.get("tabname").setVisible(true);