buffer: fix comments in bidirectionalIndexOf

PR-URL: #10162
Fixes: #9801
Reviewed-By: Roman Reiss <[email protected]>
Reviewed-By: Stephen Belanger <[email protected]>
Reviewed-By: Trevor Norris <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Sakthipriyan Vairamani <[email protected]>
Reviewed-By: Rich Trott <[email protected]>

Author: dcposch

lib/buffer.js

@@ -580,9 +580,10 @@ function bidirectionalIndexOf(buffer, val, byteOffset, encoding, dir) {
   } else if (byteOffset < -0x80000000) {
     byteOffset = -0x80000000;
   }
-  byteOffset = +byteOffset;  // Coerce to Number.
-  if (isNaN(byteOffset)) {
-    // If the offset is undefined, null, NaN, "foo", etc, search whole buffer.
+  // Coerce to Number. Values like null and [] become 0.
+  byteOffset = +byteOffset;
+  // If the offset is undefined, "foo", {}, coerces to NaN, search whole buffer.
+  if (Number.isNaN(byteOffset)) {
     byteOffset = dir ? 0 : (buffer.length - 1);
   }
   dir = !!dir;  // Cast to bool.