Improve constructor error messages

Co-authored-by: Timothy Gu <timothygu99@gmail.com>

Author: ExE-Boss

index.js

@@ -1,6 +1,5 @@
 'use strict';
 const webidlWrapper = require('./webidl2js-wrapper.js');
-const webidlConversions = require('webidl-conversions');
 
 const sharedGlobalObject = {};
 webidlWrapper.install(sharedGlobalObject);
@@ -14,13 +13,11 @@ const origCSSStyleDeclaration = sharedGlobalObject.CSSStyleDeclaration;
  */
 function CSSStyleDeclaration(onChangeCallback = null) {
   if (new.target === undefined) {
-    throw new TypeError('Illegal invocation');
+    throw new TypeError("Class constructor CSSStyleDeclaration cannot be invoked without 'new'");
   }
 
-  if (onChangeCallback !== null) {
-    onChangeCallback = webidlConversions.Function(onChangeCallback, {
-      context: 'Failed to constructor CSSStyleDeclaration: parameter 1',
-    });
+  if (onChangeCallback !== null && typeof onChangeCallback !== 'function') {
+    throw new TypeError('Failed to constructor CSSStyleDeclaration: parameter 1 is not a function');
   }
 
   return webidlWrapper.create(sharedGlobalObject, undefined, { onChangeCallback });