Added Input.js

Got rid of the "on" files, refactored the rest of the code to use the functions declared in Input.js

js/Input.js

@@ -0,0 +1,26 @@
+class Input {
+    static on(event, elementId, functionCallback, ...args) {
+        //if element provided is string, get the actual element
+        const element = Util.getElement(elementId);
+
+        element.addEventListener(event,
+        function (e) {
+            // e = event
+            //this = element clicked
+            functionCallback(e, this, args);
+            //if you need to access the event or this variable, you need to add them
+            //when you define the callback, but you cant use the word this, eg:
+            //on('click', menuButton, function (e, button) {});
+        });
+    }
+
+    static onChildren(event, parentElement, functionCallback, ...args) {
+        parentElement = Util.getElement(parentElement);
+        const children = parentElement.children;
+        
+        //loop through children and add onClick listener
+        for (var i = 0; i < children.length; i++) {
+            on(event, children[i], functionCallback, args);
+        }
+    }
+}