beautiful error messages

doc/api/errors.md

@@ -1204,6 +1204,17 @@ An invalid `options.protocol` was passed.
 Both `breakEvalOnSigint` and `eval` options were set in the REPL config, which
 is not supported.
 
+<a id="ERR_INVALID_RETURN_PROPERTY"></a>
+### ERR_INVALID_RETURN_PROPERTY
+
+Thrown in case a function option does not return an expected property type.
+
+<a id="ERR_INVALID_RETURN_PROPERTY_STRING"></a>
+### ERR_INVALID_RETURN_PROPERTY_STRING
+
+Thrown in case a function option does not return an expected string property
+type.
+
 <a id="ERR_INVALID_RETURN_VALUE"></a>
 ### ERR_INVALID_RETURN_VALUE
 

lib/internal/errors.js

@@ -681,15 +681,29 @@ E('ERR_INVALID_PROTOCOL',
   TypeError);
 E('ERR_INVALID_REPL_EVAL_CONFIG',
   'Cannot specify both "breakEvalOnSigint" and "eval" for REPL', TypeError);
+E('ERR_INVALID_RETURN_PROPERTY', (input, name, prop, value) => {
+  let type;
+  if (value && value.constructor && value.constructor.name) {
+    type = `instance of ${value.constructor.name}`;
+  } else {
+    type = `type ${typeof value}`;
+  }
+  return `Expected ${input} to be returned for the ${prop} from the ` +
+         `"${name}" function but got ${type}.`;
+}, TypeError);
+E('ERR_INVALID_RETURN_PROPERTY_STRING', (input, name, prop, value) => {
+  return `Expected a valid ${input} to be returned for the ${prop} from the ` +
+         `"${name}" function but got ${value}.`;
+}, TypeError);
 E('ERR_INVALID_RETURN_VALUE', (input, name, value) => {
   let type;
   if (value && value.constructor && value.constructor.name) {
     type = `instance of ${value.constructor.name}`;
   } else {
     type = `type ${typeof value}`;
   }
-  return `Expected ${input} to be returned from the "${name}"` +
-          ` function but got ${type}.`;
+  return `Expected ${input} to be returned from the ` +
+         `"${name}" function but got ${type}.`;
 }, TypeError);
 E('ERR_INVALID_SYNC_FORK_INPUT',
   'Asynchronous forks do not support Buffer, Uint8Array or string input: %s',

lib/internal/modules/esm/loader.js

@@ -2,7 +2,8 @@
 
 const {
   ERR_INVALID_ARG_TYPE,
-  ERR_INVALID_PROTOCOL,
+  ERR_INVALID_RETURN_PROPERTY,
+  ERR_INVALID_RETURN_PROPERTY_STRING,
   ERR_MISSING_DYNAMIC_INTSTANTIATE_HOOK,
   ERR_UNKNOWN_MODULE_FORMAT
 } = require('internal/errors').codes;
@@ -57,21 +58,32 @@ class Loader {
       await this._resolve(specifier, parentURL, defaultResolve);
 
     if (typeof url !== 'string')
-      throw new ERR_INVALID_ARG_TYPE('url', 'string', url);
+      throw new ERR_INVALID_RETURN_PROPERTY(
+        'string', 'loader resolve', 'url', url
+      );
 
     if (typeof format !== 'string')
-      throw new ERR_INVALID_ARG_TYPE('format', 'string', format);
+      throw new ERR_INVALID_RETURN_PROPERTY_STRING(
+        'string', 'loader resolve', 'format', format
+      );
 
     if (format === 'builtin')
       return { url: `node:${url}`, format };
 
     if (this._resolve !== defaultResolve) {
-      // throws ERR_INVALID_URL for resolve if not valid
-      new URL(url);
+      try {
+        new URL(url);
+      } catch (e) {
+        throw new ERR_INVALID_RETURN_PROPERTY_STRING(
+          'url', 'loader resolve', 'url', url
+        );
+      }
     }
 
     if (format !== 'dynamic' && !url.startsWith('file:'))
-      throw new ERR_INVALID_PROTOCOL(url, 'file:');
+      throw new ERR_INVALID_RETURN_PROPERTY_STRING(
+        'file: url', 'loader resolve', 'url', url
+      );
 
     return { url, format };
   }

test/es-module/test-esm-loader-invalid-url.mjs

@@ -1,10 +1,12 @@
 // Flags: --experimental-modules --loader ./test/fixtures/es-module-loaders/loader-invalid-url.mjs
 /* eslint-disable node-core/required-modules */
 import assert from 'assert';
+import common from '../common';
 
 import('../fixtures/es-modules/test-esm-ok.mjs')
 .then(() => {
   assert.fail();
 }, (err) => {
-  assert.strictEqual(err.code, 'ERR_INVALID_URL');
-});
+  assert.strictEqual(err.code, 'ERR_INVALID_RETURN_PROPERTY_STRING');
+})
+.then(common.mustCall());