/** @module ember */ import { assert } from '@ember/debug'; import { flaggedInstrument } from '@ember/instrumentation'; import { join } from '@ember/runloop'; import { DEBUG } from '@glimmer/env'; import { isConst } from '@glimmer/reference'; import { get } from 'ember-metal'; import { ACTION, INVOKE, UnboundReference } from '../utils/references'; /** The `{{action}}` helper provides a way to pass triggers for behavior (usually just a function) between components, and into components from controllers. ### Passing functions with the action helper There are three contexts an action helper can be used in. The first two contexts to discuss are attribute context, and Handlebars value context. ```handlebars {{! An example of attribute context }}
{{! Examples of Handlebars value context }} {{input on-input=(action "save")}} {{yield (action "refreshData") andAnotherParam}} ``` In these contexts, the helper is called a "closure action" helper. Its behavior is simple: If passed a function name, read that function off the `actions` property of the current context. Once that function is read, or immediately if a function was passed, create a closure over that function and any arguments. The resulting value of an action helper used this way is simply a function. For example, in the attribute context: ```handlebars {{! An example of attribute context }} ``` The resulting template render logic would be: ```js var div = document.createElement('div'); var actionFunction = (function(context){ return function() { return context.actions.save.apply(context, arguments); }; })(context); div.onclick = actionFunction; ``` Thus when the div is clicked, the action on that context is called. Because the `actionFunction` is just a function, closure actions can be passed between components and still execute in the correct context. Here is an example action handler on a component: ```app/components/my-component.js import Component from '@ember/component'; export default Component.extend({ actions: { save() { this.get('model').save(); } } }); ``` Actions are always looked up on the `actions` property of the current context. This avoids collisions in the naming of common actions, such as `destroy`. Two options can be passed to the `action` helper when it is used in this way. * `target=someProperty` will look to `someProperty` instead of the current context for the `actions` hash. This can be useful when targeting a service for actions. * `value="target.value"` will read the path `target.value` off the first argument to the action when it is called and rewrite the first argument to be that value. This is useful when attaching actions to event listeners. ### Invoking an action Closure actions curry both their scope and any arguments. When invoked, any additional arguments are added to the already curried list. Actions should be invoked using the [sendAction](/api/ember/release/classes/Component/methods/sendAction?anchor=sendAction) method. The first argument to `sendAction` is the action to be called, and additional arguments are passed to the action function. This has interesting properties combined with currying of arguments. For example: ```app/components/my-component.js import Component from '@ember/component'; export default Component.extend({ actions: { // Usage {{input on-input=(action (action 'setName' model) value="target.value")}} setName(model, name) { model.set('name', name); } } }); ``` The first argument (`model`) was curried over, and the run-time argument (`event`) becomes a second argument. Action calls can be nested this way because each simply returns a function. Any function can be passed to the `{{action}}` helper, including other actions. Actions invoked with `sendAction` have the same currying behavior as demonstrated with `on-input` above. For example: ```app/components/my-input.js import Component from '@ember/component'; export default Component.extend({ actions: { setName(model, name) { model.set('name', name); } } }); ``` ```handlebars {{my-input submit=(action 'setName' model)}} ``` ```app/components/my-component.js import Component from '@ember/component'; export default Component.extend({ click() { // Note that model is not passed, it was curried in the template this.sendAction('submit', 'bob'); } }); ``` ### Attaching actions to DOM elements The third context of the `{{action}}` helper can be called "element space". For example: ```handlebars {{! An example of element space }} ``` Used this way, the `{{action}}` helper provides a useful shortcut for registering an HTML element in a template for a single DOM event and forwarding that interaction to the template's context (controller or component). If the context of a template is a controller, actions used this way will bubble to routes when the controller does not implement the specified action. Once an action hits a route, it will bubble through the route hierarchy. ### Event Propagation `{{action}}` helpers called in element space can control event bubbling. Note that the closure style actions cannot. Events triggered through the action helper will automatically have `.preventDefault()` called on them. You do not need to do so in your event handlers. If you need to allow event propagation (to handle file inputs for example) you can supply the `preventDefault=false` option to the `{{action}}` helper: ```handlebars