do not report error on non-initialized const bindings in for-in\for-of statements

src/compiler/checker.ts

@@ -11498,7 +11498,8 @@ module ts {
                     if (isBindingPattern(node.name) && !isBindingPattern(node.parent)) {
                         return grammarErrorOnNode(node, Diagnostics.A_destructuring_declaration_must_have_an_initializer);
                     }
-                    if (isConst(node)) {
+                    // const declarations should not be initialized in for-in for-of statements
+                    if (isConst(node) && node.parent.parent.kind !== SyntaxKind.ForInStatement && node.parent.parent.kind !== SyntaxKind.ForOfStatement) {
                         return grammarErrorOnNode(node, Diagnostics.const_declarations_must_be_initialized);
                     }
                 }