adding exercies for steps 2-1 and 2-2

step2-02/demo/src/components/TodoFooter.tsx

@@ -0,0 +1,23 @@
+import React from 'react';
+import { Text } from '@uifabric/experiments';
+import { Stack } from 'office-ui-fabric-react';
+import { Store } from '../store';
+import { DefaultButton } from 'office-ui-fabric-react';
+
+interface TodoFooterProps {
+  clear: () => void;
+  todos: Store['todos'];
+}
+
+export const TodoFooter = (props: TodoFooterProps) => {
+  const itemCount = Object.keys(props.todos).filter(id => !props.todos[id].completed).length;
+
+  return (
+    <Stack horizontal horizontalAlign="space-between">
+      <Text>
+        {itemCount} item{itemCount > 1 ? 's' : ''} left
+      </Text>
+      <DefaultButton onClick={() => props.clear()}>Clear Completed</DefaultButton>
+    </Stack>
+  );
+};