lib,test: minor refactoring

This refactors a couple tests to have upper case first characters
in comments and to use `input` instead of `i`.
It also adds a few TODOs and rewrites a few lines to use default
arguments and to prevent function recreation when unnecessary.

PR-URL: https://github.com/nodejs/node/pull/19445
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

1 files changed, 6 insertions, 2 deletions

diff --git a/lib/zlib.js b/lib/zlib.js
index f2233beb03..317fd83ce0 100644
--- a/lib/zlib.js
+++ b/lib/zlib.js
@@ -169,12 +169,16 @@ function flushCallback(level, strategy, callback) {
 // 4. Throws ERR_OUT_OF_RANGE for infinite numbers
 function checkFiniteNumber(number, name) {
   // Common case
-  if (number === undefined || Number.isNaN(number)) {
+  if (number === undefined) {
     return false;
   }
 
   if (Number.isFinite(number)) {
-    return true;  // is a valid number
+    return true; // Is a valid number
+  }
+
+  if (Number.isNaN(number)) {
+    return false;
   }
 
   // Other non-numbers