path: remove StringPrototypeCharCodeAt from some methods of posix

Remove `StringPrototypeCharCodeAt` from `posix.resolve`,
`posix.normalize`, `posix.parse`

Author: HBSPS

lib/path.js

@@ -1262,8 +1262,7 @@ const posix = {
       }
 
       resolvedPath = `${path}/${resolvedPath}`;
-      resolvedAbsolute =
-        StringPrototypeCharCodeAt(path, 0) === CHAR_FORWARD_SLASH;
+      resolvedAbsolute = path[0] === '/';
     }
 
     if (!resolvedAbsolute) {
@@ -1296,10 +1295,8 @@ const posix = {
     if (path.length === 0)
       return '.';
 
-    const isAbsolute =
-      StringPrototypeCharCodeAt(path, 0) === CHAR_FORWARD_SLASH;
-    const trailingSeparator =
-      StringPrototypeCharCodeAt(path, path.length - 1) === CHAR_FORWARD_SLASH;
+    const isAbsolute = path[0] === '/';
+    const trailingSeparator = path[path.length - 1] === '/';
 
     // Normalize the path
     path = normalizeString(path, !isAbsolute, '/', isPosixPathSeparator);
@@ -1639,8 +1636,8 @@ const posix = {
 
     // Get non-dir info
     for (; i >= start; --i) {
-      const code = StringPrototypeCharCodeAt(path, i);
-      if (code === CHAR_FORWARD_SLASH) {
+      const char = path[i];
+      if (char === '/') {
         // If we reached a path separator that was not part of a set of path
         // separators at the end of the string, stop now
         if (!matchedSlash) {
@@ -1655,7 +1652,7 @@ const posix = {
         matchedSlash = false;
         end = i + 1;
       }
-      if (code === CHAR_DOT) {
+      if (char === '.') {
         // If this is our first dot, mark it as the start of our extension
         if (startDot === -1)
           startDot = i;