dom-repeat中自定义事件无法触发父元素方法的问题排查

Hey there! Let's troubleshoot why your parent element isn't catching the update event from the my-item elements inside your dom-repeat template. This is a common gotcha with Polymer's shadow DOM and custom events, so here's what you need to check:

1. Ensure the custom event is properly dispatched with bubbling and composition enabled #

The most likely culprit is that your my-item element isn't dispatching the event in a way that can cross the shadow DOM boundary. By default, custom events in Polymer don't bubble and can't escape the shadow DOM unless you explicitly configure them.

In your my-item element's code, make sure you dispatch the event like this:

// Inside my-item's method where you want to trigger the event
this.dispatchEvent(new CustomEvent('update', {
  bubbles: true,        // Allows the event to bubble up the DOM tree
  composed: true,       // Lets the event cross shadow DOM boundaries
  detail: {             // Optional: pass data to the parent
    employee: this.employee
  }
}));

Without both bubbles: true and composed: true, the parent element will never receive the event.

2. Verify the parent's event handler is correctly defined #

Double-check that your updateFired method is properly declared in your my-view element's class. It should be a public method accessible to the template:

class MyView extends Polymer.Element {
  static get is() { return 'my-view'; }

  static get properties() {
    return {
      employees: {
        type: Array,
        value: () => [] // Initialize with an empty array to avoid undefined issues
      }
    };
  }

  updateFired(e) {
    console.log('Update event caught!', e.detail);
    // Add your event handling logic here
  }
}
customElements.define(MyView.is, MyView);

Make sure there are no typos in the method name (updateFired matches the on-update attribute) and that the method isn't accidentally marked as private (e.g., using #updateFired which would make it inaccessible to the template).

3. Confirm dom-repeat is rendering items correctly #

While you mentioned the my-item elements are rendering, it's worth ensuring your employees array is properly initialized and reactive. Using the properties getter with a default value (as shown above) ensures the array exists when dom-repeat tries to render, preventing unexpected template behavior.

Once you adjust the event dispatch in my-item to include bubbles: true and composed: true, your parent's updateFired method should start catching the events as expected!

内容的提问来源于stack exchange，提问作者Jose Raul Perera