n></code></td><td><p>The function that will be called whenever the <a href="/api/persisters/interfaces/persister/persister/"><code>Persister</code></a> starts or stops loading or saving.</p></td></tr><tr><th class="right">returns</th><td><code><span class="builtin">string</span></code></td><td><p></p><p>A unique <a href="/api/common/type-aliases/identity/id/"><code>Id</code></a> for the listener that can later be used to remove it.</p><p></p></td></tr></table></div><p>The provided listener is a <a href="/ap