diff --git a/lib/jsdom/browser/Window.js b/lib/jsdom/browser/Window.js
index 92989c2bf9..68704d11ac 100644
--- a/lib/jsdom/browser/Window.js
+++ b/lib/jsdom/browser/Window.js
@@ -543,14 +543,10 @@ function Window(options) {
     return declaration;
   };
 
-  const customElementRegistryImpl = CustomElementRegistry.createImpl([], {
+  this.customElements = CustomElementRegistry.create([], {
     _ownerDocument: idlUtils.implForWrapper(this._document)
   });
 
-  // TODO: move this to the document instead of the window object if possible.
-  this._customElements = customElementRegistryImpl;
-  this.customElements = idlUtils.wrapperForImpl(customElementRegistryImpl);
-
   // The captureEvents() and releaseEvents() methods must do nothing
   this.captureEvents = function () {};
 
diff --git a/lib/jsdom/browser/parser/html.js b/lib/jsdom/browser/parser/html.js
index 62352dbb04..4a3676289f 100644
--- a/lib/jsdom/browser/parser/html.js
+++ b/lib/jsdom/browser/parser/html.js
@@ -83,7 +83,6 @@ class JSDOMParse5Adapter {
       willExecuteScript = true;
     }
 
-    // TODO: need to better understand the implications of the changes here.
     const element = createElement(this._documentImpl, localName, namespace, null, isValue, willExecuteScript);
     this.adoptAttributes(element, attrs);
 
@@ -173,8 +172,6 @@ class JSDOMParse5Adapter {
 Object.assign(JSDOMParse5Adapter.prototype, serializationAdapter);
 
 function parseFragment(markup, contextElement) {
-  // TODO: Readjust the content document.
-  // Explain better
   const ownerDocument = contextElement.localName === "template" ?
     contextElement.content._ownerDocument :
     contextElement._ownerDocument;
diff --git a/lib/jsdom/living/custom-elements/CustomElementRegistry-impl.js b/lib/jsdom/living/custom-elements/CustomElementRegistry-impl.js
index 32cb4e9d0c..5523a9b5b5 100644
--- a/lib/jsdom/living/custom-elements/CustomElementRegistry-impl.js
+++ b/lib/jsdom/living/custom-elements/CustomElementRegistry-impl.js
@@ -68,7 +68,6 @@ class CustomElementRegistryImpl {
 
   // https://html.spec.whatwg.org/#dom-customelementregistry-define
   define(name, ctor, options) {
-    // TODO: Add better check if the ctor is a constructor
     if (typeof ctor !== "function" || !isConstructor(ctor)) {
       throw new TypeError("Constructor argument is not a constructor.");
     }
@@ -111,9 +110,8 @@ class CustomElementRegistryImpl {
     }
 
     if (this._elementDefinitionIsRunning) {
-      // TODO: Improve wording
       throw new DOMException(
-        "Can't define a new custom element in the middle of the definition of another one.",
+        "Invalid nested custom element definition.",
         "NotSupportedError"
       );
     }
diff --git a/lib/jsdom/living/helpers/custom-elements.js b/lib/jsdom/living/helpers/custom-elements.js
index dd75c73fcb..c825369584 100644
--- a/lib/jsdom/living/helpers/custom-elements.js
+++ b/lib/jsdom/living/helpers/custom-elements.js
@@ -154,7 +154,7 @@ function lookupCEDefinition(document, namespace, localName, isValue) {
     return definition;
   }
 
-  const registry = document._defaultView._customElements;
+  const registry = implForWrapper(document._defaultView.customElements);
 
   const definitionByName = registry._customElementDefinitions.find(def => {
     return def.name === def.localName && def.localName === localName;
diff --git a/lib/jsdom/living/helpers/html-constructor.js b/lib/jsdom/living/helpers/html-constructor.js
index 9fedf86330..3b66edb52c 100644
--- a/lib/jsdom/living/helpers/html-constructor.js
+++ b/lib/jsdom/living/helpers/html-constructor.js
@@ -85,7 +85,7 @@ const ALREADY_CONSTRUCTED_MARKER = Symbol("already-constructed-marker");
 
 // https://html.spec.whatwg.org/multipage/dom.html#htmlconstructor
 function HTMLConstructor({ globalObject, newTarget, constructorName }) {
-  const registry = globalObject._customElements;
+  const registry = implForWrapper(globalObject.customElements);
 
   if (newTarget === HTMLConstructor) {
     throw new TypeError("Invalid constructor");