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Actions

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Your app will often need a way to let users interact with controls that change application state. For example, imagine that you have a template that shows a blog title, and supports expanding the post to show the body.

If you add the {{action}} helper to any HTML DOM element, when a user clicks the element, the named event will be sent to the template's corresponding component or controller.

app/templates/components/single-post.hbs
<h3><button {{action "toggleBody"}}>{{this.title}}</button></h3>
{{#if this.isShowingBody}}
  <p>{{this.body}}</p>
{{/if}}

In the component or controller, you can then define what the action does within the actions hook:

app/components/single-post.js
import Component from '@ember/component';

export default Component.extend({
  actions: {
    toggleBody() {
      this.toggleProperty('isShowingBody');
    }
  }
});

You will learn about more advanced usages in the Component's Triggering Changes With Actions guide, but you should familiarize yourself with the following basics first.

Action Parameters

You can optionally pass arguments to the action handler. Any values passed to the {{action}} helper after the action name will be passed to the handler as arguments.

For example, if the post argument was passed:

<p><button {{action "select" this.post}}>✓</button> {{this.post.title}}</p>

The select action handler would be called with a single argument containing the post model:

app/components/single-post.js
import Component from '@ember/component';

export default Component.extend({
  actions: {
    select(post) {
      console.log(post.get('title'));
    }
  }
});

Specifying the Type of Event

By default, the {{action}} helper listens for click events and triggers the action when the user clicks on the element.

You can specify an alternative event by using the on option.

<p>
  <button {{action "select" this.post on="mouseUp"}}>✓</button>
  {{this.post.title}}
</p>

You should use the camelCased event names, so two-word names like keypress become keyPress.

Allowing Modifier Keys

By default, the {{action}} helper will ignore click events with pressed modifier keys. You can supply an allowedKeys option to specify which keys should not be ignored.

<button {{action "anActionName" allowedKeys="alt"}}>
  click me
</button>

This way the {{action}} will fire when clicking with the alt key pressed down.

Allowing Default Browser Action

By default, the {{action}} helper prevents the default browser action of the DOM event (i.e. going to newPage.htm). So, for example see the following standard a tag with an action:

<a href="newPage.htm" {{action "logClick"}}>Go</a>

Clicking on this link does not go to newPage.htm because the action has overridden this functionality. This is the default behavior for Ember.

You can override this behavior and make this work more like a standard, non-ember, anchor tag by using the preventDefault=false overload of the action on an a tag. For example:

<a href="newPage.htm" {{action "logClick" preventDefault=false}}>Go</a>

This still triggers the logClick action but then we also go to newPage.htm.

You can specify preventDefault=true and this reverts to the standard Ember functionality (see previous example).

Modifying the action's first parameter

If a value option for the {{action}} helper is specified, its value will be considered a property path that will be read off of the first parameter of the action. This comes very handy with event listeners and enables to work with one-way bindings.

<label>What's your favorite band?</label>
<input type="text" value={{this.favoriteBand}} onblur={{action "bandDidChange"}} />

Let's assume we have an action handler that prints its first parameter:

actions: {
  bandDidChange(newValue) {
    console.log(newValue);
  }
}

By default, the action handler receives the first parameter of the event listener, the event object the browser passes to the handler, so bandDidChange prints Event {}.

Using the value option modifies that behavior by extracting that property from the event object:

<label>What's your favorite band?</label>
<input type="text" value={{this.favoriteBand}} onblur={{action "bandDidChange" value="target.value"}} />

The newValue parameter thus becomes the target.value property of the event object, which is the value of the input field the user typed. (e.g 'Foo Fighters')

Attaching Actions to Non-Clickable Elements

Note that while Ember currently permits you to add an action to any DOM element, not all DOM elements are eligible to receive focus, according to HTML standards.

For example, if an action is attached to an a link without an href attribute, or to a div, some browsers won't execute the associated function.

Always check to see that the element you are adding an action to is interactive, according to web accessibility and browser standards. As a rule of thumb, if you find yourself adding an action an <a> tag, you should turn it into a <button> instead.

For more information about building accessible apps in Ember, see the Accessibility Guide.

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