disconnectedCallback()

The browser calls a custom element's disconnectedCallback when the element is removed from the page. StacheElement uses this to clean up event handlers and call the disconnected lifecycle hook.

The disconnectedCallback can also be called manually to trigger these things:

import { StacheElement } from "can";

class MyElement extends StacheElement {
    connected() {
        this.listenTo("greeting", (greeting) => {
            console.log(`greeting changed to ${greeting}`);
        });
    }
}
customElements.define("my-el", MyElement);

const myEl = new MyElement()
    .connectedCallback();

myEl.greeting = "Hello"; // -> "greeting changed to Hello"

myEl.disconnectedCallback(); // -> "cleaned up"

myEl.greeting = "Hi"; // nothing logged
myEl.greeting = "Hello";

myEl.disconnectedCallback();