esm: skip file: URL conversion to path when possible

Author: aduh95

lib/internal/modules/esm/get_format.js

@@ -4,9 +4,10 @@ const {
   ObjectPrototypeHasOwnProperty,
   PromisePrototypeThen,
   PromiseResolve,
+  StringPrototypeCharCodeAt,
   StringPrototypeSlice,
 } = primordials;
-const { basename, extname, relative } = require('path');
+const { basename, relative } = require('path');
 const { getOptionValue } = require('internal/options');
 const {
   extensionFormatMap,
@@ -41,15 +42,37 @@ function getDataProtocolModuleFormat(parsed) {
   return mimeToFormat(mime);
 }
 
+const DOT_CODE = 46;
+const SLASH_CODE = 47;
+
+/**
+ * Returns the file extension from a file: URL. Should give similar result than
+ * require('node:path').extname(require('node:url').fileURLToPath(url)).
+ * @param {URL} url A file: URL.
+ * @returns {string}
+ */
+function extname(url) {
+  const { pathname } = url;
+  for (let i = pathname.length - 1; i > 0; i--) {
+    switch (StringPrototypeCharCodeAt(pathname, i)) {
+      case SLASH_CODE:
+        return '';
+
+      case DOT_CODE:
+        return StringPrototypeSlice(pathname, i);
+    }
+  }
+  return '';
+}
+
 /**
  * @param {URL} url
  * @param {{parentURL: string}} context
  * @param {boolean} ignoreErrors
  * @returns {string}
  */
 function getFileProtocolModuleFormat(url, context, ignoreErrors) {
-  const filepath = fileURLToPath(url);
-  const ext = extname(filepath);
+  const ext = extname(url);
   if (ext === '.js') {
     return getPackageType(url) === 'module' ? 'module' : 'commonjs';
   }
@@ -59,6 +82,7 @@ function getFileProtocolModuleFormat(url, context, ignoreErrors) {
 
   // Explicit undefined return indicates load hook should rerun format check
   if (ignoreErrors) { return undefined; }
+  const filepath = fileURLToPath(url);
   let suggestion = '';
   if (getPackageType(url) === 'module' && ext === '') {
     const config = getPackageScopeConfig(url);