console,util: avoid pair array generation in C++

Use a plain `[key, value, key, value]`-style list instead
of an array of pairs for inspecting collections.

This also fixes a bug with `console.table()` where
inspecting a non-key-value `MapIterator` would have
led to odd results.

PR-URL: https://github.com/nodejs/node/pull/20831
Refs: https://github.com/nodejs/node/pull/20719#discussion_r189342513
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

1 files changed, 6 insertions, 19 deletions

diff --git a/src/node_util.cc b/src/node_util.cc
index 724bb3603c..ef7dc8a818 100644
--- a/src/node_util.cc
+++ b/src/node_util.cc
@@ -53,29 +53,16 @@ static void PreviewEntries(const FunctionCallbackInfo<Value>& args) {
   if (!args[0]->IsObject())
     return;
 
+  Environment* env = Environment::GetCurrent(args);
   bool is_key_value;
   Local<Array> entries;
   if (!args[0].As<Object>()->PreviewEntries(&is_key_value).ToLocal(&entries))
     return;
-  if (!is_key_value)
-    return args.GetReturnValue().Set(entries);
-
-  uint32_t length = entries->Length();
-  CHECK_EQ(length % 2, 0);
-
-  Environment* env = Environment::GetCurrent(args);
-  Local<Context> context = env->context();
-
-  Local<Array> pairs = Array::New(env->isolate(), length / 2);
-  for (uint32_t i = 0; i < length / 2; i++) {
-    Local<Array> pair = Array::New(env->isolate(), 2);
-    pair->Set(context, 0, entries->Get(context, i * 2).ToLocalChecked())
-        .FromJust();
-    pair->Set(context, 1, entries->Get(context, i * 2 + 1).ToLocalChecked())
-        .FromJust();
-    pairs->Set(context, i, pair).FromJust();
-  }
-  args.GetReturnValue().Set(pairs);
+  Local<Array> ret = Array::New(env->isolate(), 2);
+  ret->Set(env->context(), 0, entries).FromJust();
+  ret->Set(env->context(), 1, v8::Boolean::New(env->isolate(), is_key_value))
+      .FromJust();
+  return args.GetReturnValue().Set(ret);
 }
 
 // Side effect-free stringification that will never throw exceptions.