lib: prefer number to string in webidl type function

PR-URL: #55489
Reviewed-By: Matthew Aitken <maitken033380023@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

lib/internal/webidl.js

@@ -29,6 +29,15 @@ const { kEmptyObject } = require('internal/util');
 
 const converters = { __proto__: null };
 
+const UNDEFINED = 1;
+const BOOLEAN = 2;
+const STRING = 3;
+const SYMBOL = 4;
+const NUMBER = 5;
+const BIGINT = 6;
+const NULL = 7;
+const OBJECT = 8;
+
 /**
  * @see https://webidl.spec.whatwg.org/#es-any
  * @param {any} V
@@ -39,7 +48,7 @@ converters.any = (V) => {
 };
 
 converters.object = (V, opts = kEmptyObject) => {
-  if (type(V) !== 'Object') {
+  if (type(V) !== OBJECT) {
     throw makeException(
       'is not an object',
       kEmptyObject,
@@ -236,37 +245,37 @@ function createEnumConverter(name, values) {
 
 // https://tc39.es/ecma262/#sec-ecmascript-data-types-and-values
 function type(V) {
-  if (V === null)
-    return 'Null';
-
   switch (typeof V) {
     case 'undefined':
-      return 'Undefined';
+      return UNDEFINED;
     case 'boolean':
-      return 'Boolean';
+      return BOOLEAN;
     case 'number':
-      return 'Number';
+      return NUMBER;
     case 'string':
-      return 'String';
+      return STRING;
     case 'symbol':
-      return 'Symbol';
+      return SYMBOL;
     case 'bigint':
-      return 'BigInt';
+      return BIGINT;
     case 'object': // Fall through
     case 'function': // Fall through
     default:
+      if (V === null) {
+        return NULL;
+      }
       // Per ES spec, typeof returns an implementation-defined value that is not
       // any of the existing ones for uncallable non-standard exotic objects.
       // Yet Type() which the Web IDL spec depends on returns Object for such
       // cases. So treat the default case as an object.
-      return 'Object';
+      return OBJECT;
   }
 }
 
 // https://webidl.spec.whatwg.org/#es-sequence
 function createSequenceConverter(converter) {
   return function(V, opts = kEmptyObject) {
-    if (type(V) !== 'Object') {
+    if (type(V) !== OBJECT) {
       throw makeException(
         'can not be converted to sequence.',
         opts);