angular-docs-cn/aio/content/guide/event-binding-concepts.md

# How event binding works

In an event binding, Angular configures an event handler for the target event.
You can use event binding with your own custom events.

When the component or directive raises the event, the handler executes the template statement.
The template statement performs an action in response to the event.

## Handling events

A common way to handle events is to pass the event object, `$event`, to the method handling the event.
The `$event` object often contains information the method needs, such as a user's name or an image URL.

The target event determines the shape of the `$event` object.
If the target event is a native DOM element event, then `$event` is a [DOM event object](https://developer.mozilla.org/en-US/docs/Web/Events), with properties such as `target` and `target.value`.

In the following example the code sets the `<input>` `value` property by binding to the `name` property.


<code-example path="event-binding/src/app/app.component.html" region="event-binding-3" header="src/app/app.component.html"></code-example>

With this example, the following actions occur:

1. The code binds to the `input` event of the `<input>` element, which allows the code to listen for changes.
1. When the user makes changes, the component raises the `input` event.
1. The binding executes the statement within a context that includes the DOM event object, `$event`.
1. Angular retrieves the changed text by calling `getValue($event.target)` and updates the `name` property.

If the event belongs to a directive or component, `$event` has the shape that the directive or component produces.

<div class="alert is-helpful">

The type of `$event.target` is only `EventTarget` in the template.
In the `getValue()` method, the target is cast to an `HTMLInputElement` to allow type-safe access to its `value` property.

<code-example path="event-binding/src/app/app.component.ts" region="getValue"></code-example>

</div>