Add support for loading before DOMContentLoaded

fixes jcgertig#33

date-input-polyfill.js

@@ -9,15 +9,20 @@ const addPickers = () => {
   }
 };
 
-// Run the above code on any <input type="date"> in the document, also on dynamically created ones.
-addPickers();
-
-document.addEventListener(`DOMContentLoaded`, () => {
+const init = () => {
+  // Run the above code on any <input type="date"> in the document, also on dynamically created ones.
   addPickers();
-});
+  // This is also on mousedown event so it will capture new inputs that might
+  // be added to the DOM dynamically.
+  document.querySelector(`body`).addEventListener(`mousedown`, () => {
+    addPickers();
+  });
+};
 
-// This is also on mousedown event so it will capture new inputs that might
-// be added to the DOM dynamically.
-document.querySelector(`body`).addEventListener(`mousedown`, () => {
-  addPickers();
-});
+if (document.readyState !== `loading`) {
+  init();
+} else {
+  document.addEventListener(`DOMContentLoaded`, () => {
+    init();
+  });
+}