diff --git a/packages/fcl-js/src/jstree.pp b/packages/fcl-js/src/jstree.pp
index f6267d09cc..935dd395d3 100644
--- a/packages/fcl-js/src/jstree.pp
+++ b/packages/fcl-js/src/jstree.pp
@@ -230,7 +230,7 @@ Type
     Property Elements[AIndex : Integer] : TJSArrayLiteralElement Read GetE ; default;
   end;
 
-  { TJSArrayLiteral - [element1,...] }
+  { TJSArrayLiteral - [element1,...] or Args of a function }
 
   TJSArrayLiteral = Class(TJSElement)
   private
@@ -328,6 +328,7 @@ Type
   Public
     Destructor Destroy; override;
     procedure AddArg(El: TJSElement);
+    procedure InsertArg(Index: integer; El: TJSElement);
     Property Expr : TJSElement Read FExpr Write FExpr;
     Property Args : TJSArguments Read FArgs Write FArgs;
   end;
@@ -1698,6 +1699,14 @@ begin
   Args.Elements.AddElement.Expr:=El;
 end;
 
+procedure TJSCallExpression.InsertArg(Index: integer; El: TJSElement);
+var
+  NewEl: TJSArrayLiteralElement;
+begin
+  NewEl:=TJSArrayLiteralElement(Args.Elements.Insert(Index));
+  NewEl.Expr:=El;
+end;
+
 { TJSUnary }
 
 Class function TJSUnary.PrefixOperatorToken: tjsToken;