fix: Add a command to properly extend class methods

frappe/public/js/frappe/form/script_manager.js

@@ -3,6 +3,13 @@
 
 frappe.provide("frappe.ui.form.handlers");
 
+window.extend_cscript = (cscript, controller_object) => {
+	$.extend(cscript, controller_object);
+	if (controller_object.__proto__) {
+		cscript.__proto__ = controller_object.__proto__;
+	}
+};
+
 frappe.ui.form.get_event_handler_list = function(doctype, fieldname) {
 	if(!frappe.ui.form.handlers[doctype]) {
 		frappe.ui.form.handlers[doctype] = {};