Fixes in codegen and test script

lib/src/codegen/js_codegen.dart

Index: lib/src/codegen/js_codegen.dart
diff --git a/lib/src/codegen/js_codegen.dart b/lib/src/codegen/js_codegen.dart
index 1c70c19e778f183bf0a2e1a6ead9be4107a7bd07..6f135f0d21cad9d566835518470bb9e35b167124 100644
--- a/lib/src/codegen/js_codegen.dart
+++ b/lib/src/codegen/js_codegen.dart
@@ -1537,7 +1537,9 @@ class JSCodegenVisitor extends GeneralizingAstVisitor with ConversionVisitor {
     if (node.catchKeyword != null) {
       var name = node.exceptionParameter;
       if (name != null && name.name != _catchParameter) {
-        body.add(js.statement('let # = #;', [_visit(name), _catchParameter]));
+        var decl = new JS.VariableDeclaration(name.name);
+        decl.sourceInformation = name;
+        body.add(js.statement('let # = #;', [decl, _catchParameter]));
         _catchParameter = name.name;
       }
       if (node.stackTraceParameter != null) {