You can create get/set properties by using the underscore suffix.

<pre class="runnable readonly text 300">
class Simple extends Base {
    static getConfig() {
        return {
            className: 'Demo.view.component.Simple',
            ntype: 'demo-simple-component',

            foo: 1, // An instance field

            bar_: null, // A get/set field with lifecycle hooks

        }
    }
}
</pre>

In the debugger console this shows up as a get/set property.

<pre style="color:gray;">
    <span style="color:DarkOrchid">bar</span>: (...)
</pre>