fs: replace magic numbers by named constants

PR-URL: nodejs#18757
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Vladimir de Turckheim <vlad2t@hotmail.com>

lib/fs.js

@@ -46,6 +46,10 @@ const {
   assertEncoding,
   stringToFlags
 } = internalFS;
+const {
+  CHAR_FORWARD_SLASH,
+  CHAR_BACKWARD_SLASH,
+} = require('internal/constants');
 
 Object.defineProperty(exports, 'constants', {
   configurable: false,
@@ -1796,7 +1800,7 @@ if (isWindows) {
 } else {
   splitRoot = function splitRoot(str) {
     for (var i = 0; i < str.length; ++i) {
-      if (str.charCodeAt(i) !== 47/*'/'*/)
+      if (str.charCodeAt(i) !== CHAR_FORWARD_SLASH)
         return str.slice(0, i);
     }
     return str;
@@ -1820,7 +1824,9 @@ if (isWindows) {
   nextPart = function nextPart(p, i) {
     for (; i < p.length; ++i) {
       const ch = p.charCodeAt(i);
-      if (ch === 92/*'\'*/ || ch === 47/*'/'*/)
+
+      // Check for a separator character
+      if (ch === CHAR_BACKWARD_SLASH || ch === CHAR_FORWARD_SLASH)
         return i;
     }
     return -1;