> For the complete documentation index, see [llms.txt](https://docs.fact-finder.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.fact-finder.com/webcomponents-overview/web-components-4.x./guides/advanced/custom-components.md).

# Custom Components

Build custom components with FactFinder events and result subscriptions.

FactFinder Web Components API can be used to implement custom components in any web framework.

In a typical scenario, use [EventAggregator's](file:///api/4.x/core-event-aggregator) `addFFEvent()` to query FactFinder and [ResultDispatcher's](file:///api/4.x/core-result-dispatcher) `subscribe()` to receive its response.

Below are two examples implementing a product carousel component: one in VueJS and one as a native custom element.

### VueJS

The source code is available [here](https://github.com/FACT-Finder-Web-Components/demos/blob/release/4.x/custom-components/vuejs-carousel/carousel.js).

{% stepper %}
{% step %}

#### `addFFEvent`

Call `addFFEvent()` in the `mounted` hook to trigger a FactFinder search when the component renders for the first time:

```javascript
eventAggregator.addFFEvent({
    type: 'search',
    query: carousel.query,
    topics: function () {
        return ['carousel-' + carousel._uid];
    }
});
```

* `type: 'search'` indicates that we want to perform a regular search.
* `query` is populated from the component prop.
* The `topics` function defines to which topic the results will be dispatched. In this case, this topic should be unique for each component instance. Otherwise, other carousels would interfere with each other.

{% hint style="info" %}
When designing a production-ready component, it is advisable to implement a `query` prop watcher to react to its possible changes with consecutive search requests.
{% endhint %}
{% endstep %}

{% step %}

#### `subscribe`

Subscribe to the same topic in the `mounted` hook:

```javascript
carousel.subscriptionKey = resultDispatcher.subscribe('carousel-' + carousel._uid, function (response) {
    carousel.records = response.searchResult.records.map(function (record) {
        return record.record;
    });
});
```

Here, extract all the information needed from the response and store it in component data alongside the subscription key returned by `subscribe()`.
{% endstep %}

{% step %}

#### `unsubscribe`

Before destroying the component, unsubscribe using the previously stored subscription key:

```javascript
if (carousel.subscriptionKey) {
    resultDispatcher.unsubscribe('carousel-' + carousel._uid, carousel.subscriptionKey);
}
```

{% endstep %}
{% endstepper %}

### Native custom element

The source code is available [here](https://github.com/FACT-Finder-Web-Components/demos/blob/release/4.x/custom-components/native-carousel/carousel.js).

The usage of FactFinder Web Components API here is very similar to the usage in the VueJS example.

{% stepper %}
{% step %}

#### `addFFEvent`

The `addFFEvent()` call is almost identical:

```javascript
eventAggregator.addFFEvent({
    type: 'search',
    query: query,
    topics: function () {
        return ['carousel-' + uid];
    }
});
```

Here, invoke it in the `attributeChangedCallback`, meaning whenever a new value of the `query` attribute is set, trigger a new search.
{% endstep %}

{% step %}

#### `subscribe`

Subscribe in the `connectedCallback`:

```javascript
element._subscriptionKey = resultDispatcher.subscribe('carousel-' + element._uid, handleRecords(element));
...
function handleRecords(element) {
    return function(response) {
        element._records = response.searchResult.records;
        element._carouselContainer.innerHTML = element._records.map(renderProduct).join('');
    };
}
```

Just like in the previous example, store the subscription key and returned records.

As no automatic renderer is used, perform the rendering here.
{% endstep %}

{% step %}

#### `unsubscribe`

Unsubscribe in the `disconnectedCallback`:

```javascript
resultDispatcher.unsubscribe('carousel-' + element._uid, element._subscriptionKey);
```

{% endstep %}
{% endstepper %}


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