bug/issue 144 check CE registry before assuming a custom element defi…

…nition exists (#146)

* refactor and use registry check for ecxisting custom elements

* track custom elements registry spec slignment TODO

* fix linting

* refactor and TODO comment for spec alignment

* correct comment

src/dom-shim.js

@@ -123,15 +123,20 @@ class HTMLTemplateElement extends HTMLElement {
 // https://developer.mozilla.org/en-US/docs/Web/API/CustomElementRegistry
 class CustomElementsRegistry {
   constructor() {
-    this.customElementsRegistry = {};
+    // TODO this should probably be a set or otherwise follow the spec?
+    // https://github.com/ProjectEvergreen/wcc/discussions/145
+    this.customElementsRegistry = new Map();
   }
 
   define(tagName, BaseClass) {
-    this.customElementsRegistry[tagName] = BaseClass;
+    // TODO this should probably fail as per the spec...
+    // e.g. if(this.customElementsRegistry.get(tagName))
+    // https://github.com/ProjectEvergreen/wcc/discussions/145
+    this.customElementsRegistry.set(tagName, BaseClass);
   }
 
   get(tagName) {
-    return this.customElementsRegistry[tagName];
+    return this.customElementsRegistry.get(tagName);
   }
 }
 

src/wcc.js

@@ -134,9 +134,7 @@ async function initializeCustomElement(elementURL, tagName, attrs = [], definiti
 
   // https://github.com/ProjectEvergreen/wcc/pull/67/files#r902061804
   const { pathname } = elementURL;
-  const element = tagName
-    ? customElements.get(tagName)
-    : (await import(pathname)).default;
+  const element = customElements.get(tagName) ?? (await import(pathname)).default;
   const dataLoader = (await import(pathname)).getData;
   const data = props
     ? props