feat(dom): Convert JS to TypeScript

Refs #4225

Author: acdvorak

packages/mdc-dom/index.js

@@ -21,6 +21,6 @@
  * THE SOFTWARE.
  */
 
-import * as ponyfill from './ponyfill';
+import * as ponyfill from './ponyfill.ts';
 
 export {ponyfill};

packages/mdc-dom/ponyfill.js renamed to packages/mdc-dom/ponyfill.ts

@@ -26,12 +26,11 @@
  * This makes ponyfills safer than traditional polyfills, especially for libraries like MDC.
  */
 
-/**
- * @param {!Element} element
- * @param {string} selector
- * @return {?Element}
- */
-function closest(element, selector) {
+interface MsElement extends Element {
+  msMatchesSelector(selector: string): boolean;
+}
+
+function closest(element: Element, selector: string): Element | null {
   if (element.closest) {
     return element.closest(selector);
   }
@@ -46,15 +45,10 @@ function closest(element, selector) {
   return null;
 }
 
-/**
- * @param {!Element} element
- * @param {string} selector
- * @return {boolean}
- */
-function matches(element, selector) {
+function matches(element: Element, selector: string): boolean {
   const nativeMatches = element.matches
-    || element.webkitMatchesSelector
-    || element.msMatchesSelector;
+      || element.webkitMatchesSelector
+      || (element as MsElement).msMatchesSelector;
   return nativeMatches.call(element, selector);
 }