> For the complete documentation index, see [llms.txt](https://lochiwei.gitbook.io/web/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://lochiwei.gitbook.io/web/browser/event/handler/register/handler-options.md).

# handler options

[JS](/web/js.md) ⟩ [browser](/web/browser.md) ⟩ [event](/web/browser/event.md) ⟩ [handler](/web/browser/event/handler.md) ⟩ [register](/web/browser/event/handler/register.md) ⟩ options

{% hint style="success" %}

```javascript
elem.addEventListener(event, handler, {
    once: true,    // automatically removed after it triggers.
    capture: true, // capturing phase
    passive: true, // handler won't call preventDefault()
});
```

* `capture`: -> [Bubbling and capturing](https://javascript.info/bubbling-and-capturing). <mark style="color:blue;">`options`</mark> can also be <mark style="color:yellow;">`false/true`</mark>, that’s the same as <mark style="color:yellow;">`{capture: false/true}`</mark>.
* `passive`: -> [Browser default actions](https://javascript.info/default-browser-action).
  {% endhint %}

{% tabs %}
{% tab title="⭐️ 重點" %}
{% hint style="info" %}
If you pass <mark style="color:purple;">**true**</mark> to the optional <mark style="color:yellow;">**3rd argument**</mark> to [addEventListener()](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener),  the handler is registered as a [**capturing event handler**](/web/browser/event/propagation/capturing.md).

```javascript
elem.addEventListener(event, handler, true);
```

{% endhint %}
{% endtab %}

{% tab title="📗 參考" %}

* [ ] javascript.info ⟩ [Introduction to browser events](https://javascript.info/introduction-browser-events#addeventlistener)
  {% endtab %}
  {% endtabs %}