LibJS: Replace iterator hint string argument with an enum

There's no reason at all for this to be a string or to accept arbitrary
values - just because it's displayed as strings in the spec doesn't mean
we have to do the same :^)

Userland/Libraries/LibJS/Runtime/IteratorOperations.cpp

@@ -10,12 +10,11 @@
 
 namespace JS {
 
-Object* get_iterator(GlobalObject& global_object, Value value, String hint, Value method)
+Object* get_iterator(GlobalObject& global_object, Value value, IteratorHint hint, Value method)
 {
     auto& vm = global_object.vm();
-    VERIFY(hint == "sync" || hint == "async");
     if (method.is_empty()) {
-        if (hint == "async")
+        if (hint == IteratorHint::Async)
             TODO();
         auto object = value.to_object(global_object);
         if (!object)
@@ -100,7 +99,7 @@ void get_iterator_values(GlobalObject& global_object, Value value, AK::Function<
 {
     auto& vm = global_object.vm();
 
-    auto iterator = get_iterator(global_object, value, "sync", method);
+    auto iterator = get_iterator(global_object, value, IteratorHint::Sync, method);
     if (!iterator)
         return;
 

Userland/Libraries/LibJS/Runtime/IteratorOperations.h

@@ -14,7 +14,12 @@ namespace JS {
 // Common iterator operations defined in ECMA262 7.4
 // https://tc39.es/ecma262/#sec-operations-on-iterator-objects
 
-Object* get_iterator(GlobalObject&, Value value, String hint = "sync", Value method = {});
+enum class IteratorHint {
+    Sync,
+    Async,
+};
+
+Object* get_iterator(GlobalObject&, Value value, IteratorHint hint = IteratorHint::Sync, Value method = {});
 bool is_iterator_complete(Object& iterator_result);
 Value create_iterator_result_object(GlobalObject&, Value value, bool done);
 

Userland/Libraries/LibJS/Runtime/VM.cpp

@@ -180,7 +180,7 @@ void VM::assign(const NonnullRefPtr<BindingPattern>& target, Value value, Global
 
     switch (binding.kind) {
     case BindingPattern::Kind::Array: {
-        auto iterator = get_iterator(global_object, value, "sync"sv, {});
+        auto iterator = get_iterator(global_object, value);
         if (!iterator)
             return;