marko/packages/runtime-class/test/components-browser/fixtures/sanity-check-custom-event/index.marko

<div>
    <app-foo onTest('handleFooTest')/>
</div>

class {
    onMount() {
        var fooEl = document.querySelector('.foo');
        var fooComponent = this.fooComponent = require('marko/components').getComponentForEl(fooEl);
        fooComponent.emitTestEvent();
    }
    handleFooTest() {
        this.fooEvent = arguments;
    }
}