[minor]

frappe/public/js/legacy/clientscriptAPI.js

@@ -248,13 +248,14 @@ _f.Frm.prototype.clear_table = function(fieldname) {
 _f.Frm.prototype.add_child = function(fieldname, values) {
 	var doc = frappe.model.add_child(this.doc, frappe.meta.get_docfield(this.doctype, fieldname).options, fieldname);
 	if(values) {
-		// Deep clone
-		var d = JSON.parse(JSON.stringify(values));
-
 		// Values of unique keys should not be overridden
+		var d = {};
 		var unique_keys = ["idx", "name"];
-		unique_keys.map((key) => {
-			d[key] && delete d[key];
+
+		Object.keys(values).map((key) => {
+			if(!unique_keys.includes(key)) {
+				d[key] = values[key];
+			}
 		});
 
 		$.extend(doc, d);