Disable fields on CRM Form - CRM 2015/ 2013/ 2011

function DisableForm() {

    Xrm.Page.ui.controls.forEach(

     function (control, index) {

         if (control.getControlType() != "subgrid" && control.getControlType() != "iframe" && control.getControlType() != "webresource")

             control.setDisabled(true);

     });

}