ldcard.</p></td></tr><tr><th><code>listener</code></th><td><code><span class="type"><a href="/api/metrics/type-aliases/listener/metriclistener/">MetricListener</a></span></code></td><td><p>The function that will be called whenever the <a href="/api/metrics/type-aliases/metric/metric/"><code>Metric</code></a> changes.</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