fix: add .js extensions to es build for Node ESM

README.md

@@ -46,15 +46,17 @@ import validator from 'validator';
 Or, import only a subset of the library:
 
 ```javascript
-import isEmail from 'validator/lib/isEmail';
+import isEmail from 'validator/lib/isEmail.js';
 ```
 
 #### Tree-shakeable ES imports
 
 ```javascript
-import isEmail from 'validator/es/lib/isEmail';
+import isEmail from 'validator/es/lib/isEmail.js';
 ```
 
+When using native Node.js ESM, include the `.js` file extension in import specifiers.
+
 ### Client-side usage
 
 The library can be loaded either as a standalone script, or through an [AMD][amd]-compatible loader

package.json

@@ -63,7 +63,7 @@
     "clean": "run-p clean:*",
     "minify": "uglifyjs validator.js -o validator.min.js  --compress --mangle --comments /Copyright/",
     "build:browser": "node --require @babel/register build-browser && npm run minify",
-    "build:es": "babel src -d es --env-name=es",
+    "build:es": "babel src -d es --env-name=es && node scripts/add-es-import-extensions.js",
     "build:node": "babel src -d .",
     "build": "run-p build:*",
     "pretest": "npm run build && npm run lint",

scripts/add-es-import-extensions.js

@@ -0,0 +1,41 @@
+const fs = require('fs');
+const path = require('path');
+
+const ES_ROOT = path.join(__dirname, '..', 'es');
+
+function addExtension(specifier) {
+  if (specifier.endsWith('.js')) {
+    return specifier;
+  }
+
+  return `${specifier}.js`;
+}
+
+function fixFile(filePath) {
+  const source = fs.readFileSync(filePath, 'utf8');
+  const updated = source.replace(
+    /from ['"](\.\.?\/[^'"]+)['"]/g,
+    (match, specifier) => match.replace(specifier, addExtension(specifier)),
+  );
+
+  if (updated !== source) {
+    fs.writeFileSync(filePath, updated);
+  }
+}
+
+function walk(directory) {
+  for (const entry of fs.readdirSync(directory, { withFileTypes: true })) {
+    const entryPath = path.join(directory, entry.name);
+
+    if (entry.isDirectory()) {
+      walk(entryPath);
+      continue;
+    }
+
+    if (entry.name.endsWith('.js')) {
+      fixFile(entryPath);
+    }
+  }
+}
+
+walk(ES_ROOT);