ember-on-modifier


A polyfill for the {{on}} element modifier specified by
RFC #471 "{{on}} modifier".

Installation

``
ember install ember-on-modifier
`

Compatibility

* Completely inert when running ember-source 3.11 or higher
* Tested against ember-source v2.13, v2.18, v3.4 in CI

Usage

`hbs

Click me baby, one more time!

`

`ts
import Component from '@ember/component';
import { action } from '@ember-decorators/object';

export default class BritneySpearsComponent extends Component {
@action
onClick(event: MouseEvent) {
console.log('I must confess, I still believe.');
}
}
`

The [@action decorator][@action] is used to bind the onClick method to the
component instance.

[@action]: https://github.com/emberjs/rfcs/blob/master/text/0408-decorators.md#method-binding

This is essentially equivalent to:

`ts
didInsertElement() {
super.didInsertElement();

const button = this.element.querySelector('button');
button.addEventListener('click', this.onClick);
}
`

In addition to the above {{on}} will properly tear down the event listener,
when the element is removed from the DOM. It will also re-register the event
listener, if any of the passed parameters change.

$3

You can use the {{on}} modifier multiple times on the same element, even for
the same event.

`hbs
{{on "click" this.onClick}}
{{on "click" this.anotherOnClick}}
{{on "mouseover" this.onMouseEnter}}
>
Click me baby, one more time!

`

$3

All named parameters will be passed through to
[addEventListener][addeventlistener] as the third parameter, the options hash.

[addeventlistener]: https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener

`hbs



`

This is essentially equivalent to:

`ts
didInsertElement() {
super.didInsertElement();

const div = this.element.querySelector('div');
div.addEventListener('scroll', this.onScroll, { passive: true });
}
`

#### once

To fire an event listener only once, you can pass the [once option][addeventlistener-parameters]:

`hbs
{{on "click" this.clickOnlyTheFirstTime once=true}}
{{on "click" this.clickEveryTime}}
>
Click me baby, one more time!

`

clickOnlyTheFirstTime will only be fired the first time the button is clicked.
clickEveryTime is fired every time the button is clicked, including the first
time.

[addeventlistener-parameters]: https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener#Parameters

#### capture

To listen for an event during the capture phase already, use the [capture option][addeventlistener-parameters]:

`hbs



`

#### passive

If true, you promise to not call event.preventDefault(). This allows the
browser to optimize the processing of this event and not block the UI thread.
This prevent scroll jank.

If you still call event.preventDefault(), an assertion will be raised.

`hbs



`

#### Internet Explorer 11 Support

Internet Explorer 11 has a buggy and incomplete implementation of
addEventListener: It does not accept an
[options][addeventlistener-parameters] parameter and _sometimes_ even throws
a cryptic error when passing options.

This is why this addon ships a tiny [ponyfill][ponyfill] for addEventLisener
that is used internally to emulate the once, capture and passive option.
This means that all currently known [options][addeventlistener-parameters] are
polyfilled, so that you can rely on them in your logic.

[ponyfill]: https://github.com/sindresorhus/ponyfill

$3

If you want to curry the function call / partially apply arguments, you can do
so using the [{{fn}} helper][fn-helper]:

[fn-helper]: https://github.com/emberjs/rfcs/blob/master/text/0470-fn-helper.md

`hbs
{{#each this.users as |user|}}

Delete {{user.name}}

{{/each}}
`

`ts
import Component from '@ember/component';
import { action } from '@ember-decorators/object';

interface User {
name: string;
}

export default class UserListComponent extends Component {
users: User[] = [{ name: 'Tom Dale' }, { name: 'Yehuda Katz' }];

@action
deleteUser(user: User, event: MouseEvent) {
event.preventDefault();
this.users.removeObject(user);
}
}
`

$3

The old [{{action}} modifier][action-event-propagation] used to allow easily
calling event.preventDefault() like so:

`hbs
Click me
`

[action-event-propagation]: https://www.emberjs.com/api/ember/release/classes/Ember.Templates.helpers/methods/action?anchor=action#event-propagation

You also could easily call event.stopPropagation() to avoid bubbling like so:

`hbs
Click me
`

You can still do this using [ember-event-helpers][ember-event-helpers]:

[ember-event-helpers]: https://github.com/buschtoens/ember-event-helpers

`hbs
Click me
`

`hbs
Click me
`

Related Projects

- [ember-on-helper][ember-on-helper]: A complimentary {{on} template
helper that accepts arbitrary event targets.

`hbs
{{on eventTarget eventName eventListener}}
`

Also ships with two convenience helpers for adding event listeners to
document and window:

`hbs
{{on-document eventName eventListener}}
{{on-window eventName eventListener}}
``

[ember-on-helper]: https://github.com/buschtoens/ember-on-helper