Address PR: add comment

Author: Kanchalai Tanglertsampan

src/compiler/binder.ts

@@ -337,21 +337,24 @@ namespace ts {
                         ? Diagnostics.Cannot_redeclare_block_scoped_variable_0
                         : Diagnostics.Duplicate_identifier_0;
 
-                    // If the current node has NodeFlags.Default (e.g. if the node is class declaration or function declaration)
-                    // and there is already another default export (i.e. symbol.declarations is not empty), we need to report such error
+                    // If the current node is a default export of some sort, then check if
+                    // there are any other default exports that we need to error on.
+                    // We'll know whether we have other default exports depending on if `symbol` already has a declaration list set.
                     if (isDefaultExport && symbol.declarations) {
                         message = Diagnostics.A_module_cannot_have_multiple_default_exports;
                     }
-
-                    forEach(symbol.declarations, declaration => {
-                        // Error on multiple export default in the following case:
-                        // 1. multiple export default of class declaration or function declaration by checking NodeFlags.Default
-                        // 2. multiple export default of export assignment. This one doesn't have NodeFlags.Default on (as export default doesn't considered as modifiers)
-                        if ((declaration.flags & NodeFlags.Default) ||
-                            (declaration.kind === SyntaxKind.ExportAssignment && !(<ExportAssignment>node).isExportEquals)) {
-                            message = Diagnostics.A_module_cannot_have_multiple_default_exports;
-                        }
-                    });
+                    else {
+                        // This is to properly report an error in the case "export default { }" is after export default of class declaration or function declaration.
+                        forEach(symbol.declarations, declaration => {
+                            // Error on multiple export default in the following case:
+                            // 1. multiple export default of class declaration or function declaration by checking NodeFlags.Default
+                            // 2. multiple export default of export assignment. This one doesn't have NodeFlags.Default on (as export default doesn't considered as modifiers)
+                            if ((declaration.flags & NodeFlags.Default) ||
+                                (declaration.kind === SyntaxKind.ExportAssignment && !(<ExportAssignment>node).isExportEquals)) {
+                                message = Diagnostics.A_module_cannot_have_multiple_default_exports;
+                            }
+                        });
+                    }
 
                     forEach(symbol.declarations, declaration => {
                         file.bindDiagnostics.push(createDiagnosticForNode(declaration.name || declaration, message, getDisplayName(declaration)));