lib: improve normalize encoding performance

This focuses on the common case by making sure they are prioritized.
It also changes some typeof checks to test for undefined since
that is faster and it adds a benchmark.

PR-URL: https://github.com/nodejs/node/pull/18790
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

1 files changed, 6 insertions, 4 deletions

diff --git a/lib/string_decoder.js b/lib/string_decoder.js
index 04d31b2607..18097be0e6 100644
--- a/lib/string_decoder.js
+++ b/lib/string_decoder.js
@@ -43,10 +43,12 @@ const kNativeDecoder = Symbol('kNativeDecoder');
 // modules monkey-patch it to support additional encodings
 function normalizeEncoding(enc) {
   const nenc = internalUtil.normalizeEncoding(enc);
-  if (typeof nenc !== 'string' &&
-      (Buffer.isEncoding === isEncoding || !Buffer.isEncoding(enc)))
-    throw new errors.TypeError('ERR_UNKNOWN_ENCODING', enc);
-  return nenc || enc;
+  if (nenc === undefined) {
+    if (Buffer.isEncoding === isEncoding || !Buffer.isEncoding(enc))
+      throw new errors.TypeError('ERR_UNKNOWN_ENCODING', enc);
+    return enc;
+  }
+  return nenc;
 }
 
 const encodingsMap = {};