Look closely in the Busy component's template. It uses another built-in directive you have not used yet in Vue, as shown in the following example:

<Busy v-if="busy" />

Vue provides a built-in directive that affects the HTML DOM layout: v-if.
When applied to an element, the element is rendered to the DOM when the assigned expression evaluates to true; otherwise, it is removed from the DOM. Therefore, the Busy indicator is displayed only when the busy data is true.