module: improve error message for invalid data URL

Fixes: #37647

Author: aduh95

lib/internal/modules/esm/loader.js

@@ -6,6 +6,7 @@ require('internal/modules/cjs/loader');
 const {
   FunctionPrototypeBind,
   ObjectSetPrototypeOf,
+  RegExpPrototypeExec,
   SafeWeakMap,
   StringPrototypeStartsWith,
 } = primordials;
@@ -107,6 +108,13 @@ class Loader {
     }
 
     const { format } = getFormatResponse;
+    if(format === null) {
+      const dataUrl = RegExpPrototypeExec(
+        /^data:([^/]+\/[^;,]+)(?:[^,]*?)(;base64)?,/,
+        url,
+      );
+      throw new ERR_UNKNOWN_MODULE_FORMAT(dataUrl ? dataUrl[1] : 'null');
+    }
     if (typeof format !== 'string') {
       throw new ERR_INVALID_RETURN_PROPERTY_VALUE(
         'string', 'loader getFormat', 'format', format);

test/es-module/test-esm-invalid-data-urls.js

@@ -0,0 +1,18 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+
+(async () => {
+  await assert.rejects(import(`data:text/plain,export default0`), {
+    code: 'ERR_UNKNOWN_MODULE_FORMAT',
+    message: 'Unknown module format: text/plain',
+  });
+  await assert.rejects(import(`data:text/plain;base64,`), {
+    code: 'ERR_UNKNOWN_MODULE_FORMAT',
+    message: 'Unknown module format: text/plain',
+  });
+  await assert.rejects(import('data:application/json,[]'), {
+    code: 'ERR_UNKNOWN_MODULE_FORMAT',
+    message: 'Unknown module format: application/json',
+  });
+})().then(common.mustCall());