Component
Ember.Component Class
PUBLIC
Extends: Ember-CoreView
Uses: Ember.TargetActionSupport
Uses: Ember.ClassNamesSupport
Uses: Ember.ActionSupport
Uses: Ember-ViewMixin
Uses: Ember-ViewStateSupport
Defined in: packages/ember-glimmer/lib/component.js:34
Module: ember-glimmer
An Ember.Component
is a view that is completely isolated. Properties accessed in its templates go to the view object and actions are targeted at the view object. There is no access to the surrounding context or outer controller; all contextual information must be passed in.
The easiest way to create an Ember.Component
is via a template. If you name a template app/components/my-foo.hbs
, you will be able to use {{my-foo}}
in other templates, which will make an instance of the isolated component.
app/components/my-foo.hbs
{{person-profile person=currentUser}}
app/components/person-profile.hbs
<h1>{{person.title}}</h1> <img src={{person.avatar}}> <p class='signature'>{{person.signature}}</p>
You can use yield
inside a template to include the contents of any block attached to the component. The block will be executed in the context of the surrounding context or outer controller:
{{#person-profile person=currentUser}} <p>Admin mode</p> {{! Executed in the controller's context. }} {{/person-profile}}
app/components/person-profile.hbs
<h1>{{person.title}}</h1> {{! Executed in the component's context. }} {{yield}} {{! block contents }}
If you want to customize the component, in order to handle events or actions, you implement a subclass of Ember.Component
named after the name of the component.
For example, you could implement the action hello
for the person-profile
component:
app/components/person-profile.js
import Ember from 'ember'; export default Ember.Component.extend({ actions: { hello(name) { console.log("Hello", name); } } });
And then use it in the component's template:
app/templates/components/person-profile.hbs
<h1>{{person.title}}</h1> {{yield}} <!-- block contents --> <button {{action 'hello' person.name}}> Say Hello to {{person.name}} </button>
Components must have a -
in their name to avoid conflicts with built-in controls that wrap HTML elements. This is consistent with the same requirement in web components.
HTML Tag
The default HTML tag name used for a component's DOM representation is div
. This can be customized by setting the tagName
property. The following component class:
app/components/emphasized-paragraph.js
import Ember from 'ember'; export default Ember.Component.extend({ tagName: 'em' });
Would result in instances with the following HTML:
<em id="ember1" class="ember-view"></em>
HTML class
Attribute
The HTML class
attribute of a component's tag can be set by providing a classNames
property that is set to an array of strings:
app/components/my-widget.js
import Ember from 'ember'; export default Ember.Component.extend({ classNames: ['my-class', 'my-other-class'] });
Will result in component instances with an HTML representation of:
<div id="ember1" class="ember-view my-class my-other-class"></div>
class
attribute values can also be set by providing a classNameBindings
property set to an array of properties names for the component. The return value of these properties will be added as part of the value for the components's class
attribute. These properties can be computed properties:
app/components/my-widget.js
import Ember from 'ember'; export default Ember.Component.extend({ classNameBindings: ['propertyA', 'propertyB'], propertyA: 'from-a', propertyB: Ember.computed(function() { if (someLogic) { return 'from-b'; } }) });
Will result in component instances with an HTML representation of:
<div id="ember1" class="ember-view from-a from-b"></div>
If the value of a class name binding returns a boolean the property name itself will be used as the class name if the property is true. The class name will not be added if the value is false
or undefined
.
app/components/my-widget.js
import Ember from 'ember'; export default Ember.Component.extend({ classNameBindings: ['hovered'], hovered: true });
Will result in component instances with an HTML representation of:
<div id="ember1" class="ember-view hovered"></div>
When using boolean class name bindings you can supply a string value other than the property name for use as the class
HTML attribute by appending the preferred value after a ":" character when defining the binding:
app/components/my-widget.js
import Ember from 'ember'; export default Ember.Component.extend({ classNameBindings: ['awesome:so-very-cool'], awesome: true });
Will result in component instances with an HTML representation of:
<div id="ember1" class="ember-view so-very-cool"></div>
Boolean value class name bindings whose property names are in a camelCase-style format will be converted to a dasherized format:
app/components/my-widget.js
import Ember from 'ember'; export default Ember.Component.extend({ classNameBindings: ['isUrgent'], isUrgent: true });
Will result in component instances with an HTML representation of:
<div id="ember1" class="ember-view is-urgent"></div>
Class name bindings can also refer to object values that are found by traversing a path relative to the component itself:
app/components/my-widget.js
import Ember from 'ember'; export default Ember.Component.extend({ classNameBindings: ['messages.empty'], messages: Ember.Object.create({ empty: true }) });
Will result in component instances with an HTML representation of:
<div id="ember1" class="ember-view empty"></div>
If you want to add a class name for a property which evaluates to true and and a different class name if it evaluates to false, you can pass a binding like this:
app/components/my-widget.js
import Ember from 'ember'; export default Ember.Component.extend({ classNameBindings: ['isEnabled:enabled:disabled'], isEnabled: true });
Will result in component instances with an HTML representation of:
<div id="ember1" class="ember-view enabled"></div>
When isEnabled is false
, the resulting HTML representation looks like this:
<div id="ember1" class="ember-view disabled"></div>
This syntax offers the convenience to add a class if a property is false
:
app/components/my-widget.js
import Ember from 'ember'; // Applies no class when isEnabled is true and class 'disabled' when isEnabled is false export default Ember.Component.extend({ classNameBindings: ['isEnabled::disabled'], isEnabled: true });
Will result in component instances with an HTML representation of:
<div id="ember1" class="ember-view"></div>
When the isEnabled
property on the component is set to false
, it will result in component instances with an HTML representation of:
<div id="ember1" class="ember-view disabled"></div>
Updates to the value of a class name binding will result in automatic update of the HTML class
attribute in the component's rendered HTML representation. If the value becomes false
or undefined
the class name will be removed. Both classNames
and classNameBindings
are concatenated properties. See Ember.Object documentation for more information about concatenated properties.
HTML Attributes
The HTML attribute section of a component's tag can be set by providing an attributeBindings
property set to an array of property names on the component. The return value of these properties will be used as the value of the component's HTML associated attribute:
app/components/my-anchor.js
import Ember from 'ember'; export default Ember.Component.extend({ tagName: 'a', attributeBindings: ['href'], href: 'http://google.com' });
Will result in component instances with an HTML representation of:
<a id="ember1" class="ember-view" href="http://google.com" rel="external nofollow" target="_blank" rel="external nofollow" target="_blank" ></a>
One property can be mapped on to another by placing a ":" between the source property and the destination property:
app/components/my-anchor.js
import Ember from 'ember'; export default Ember.Component.extend({ tagName: 'a', attributeBindings: ['url:href'], url: 'http://google.com' });
Will result in component instances with an HTML representation of:
<a id="ember1" class="ember-view" href="http://google.com" rel="external nofollow" target="_blank" rel="external nofollow" target="_blank" ></a>
Namespaced attributes (e.g. xlink:href
) are supported, but have to be mapped, since :
is not a valid character for properties in Javascript:
app/components/my-use.js
import Ember from 'ember'; export default Ember.Component.extend({ tagName: 'use', attributeBindings: ['xlinkHref:xlink:href'], xlinkHref: '#triangle' });
Will result in component instances with an HTML representation of:
<use xlink:href="#triangle"></use>
If the return value of an attributeBindings
monitored property is a boolean the attribute will be present or absent depending on the value:
app/components/my-text-input.js
import Ember from 'ember'; export default Ember.Component.extend({ tagName: 'input', attributeBindings: ['disabled'], disabled: false });
Will result in a component instance with an HTML representation of:
<input id="ember1" class="ember-view" />
attributeBindings
can refer to computed properties:
app/components/my-text-input.js
import Ember from 'ember'; export default Ember.Component.extend({ tagName: 'input', attributeBindings: ['disabled'], disabled: Ember.computed(function() { if (someLogic) { return true; } else { return false; } }) });
To prevent setting an attribute altogether, use null
or undefined
as the return value of the attributeBindings
monitored property:
app/components/my-text-input.js
import Ember from 'ember'; export default Ember.Component.extend({ tagName: 'form', attributeBindings: ['novalidate'], novalidate: null });
Updates to the property of an attribute binding will result in automatic update of the HTML attribute in the component's rendered HTML representation. attributeBindings
is a concatenated property. See Ember.Object documentation for more information about concatenated properties.
Layouts
See Ember.Templates.helpers.yield for more information.
Responding to Browser Events
Components can respond to user-initiated events in one of three ways: method implementation, through an event manager, and through {{action}}
helper use in their template or layout.
Method Implementation
Components can respond to user-initiated events by implementing a method that matches the event name. A jQuery.Event
object will be passed as the argument to this method.
app/components/my-widget.js
import Ember from 'ember'; export default Ember.Component.extend({ click(event) { // will be called when an instance's // rendered element is clicked } });
{{action}}
Helper
See Ember.Templates.helpers.action.
Event Names
All of the event handling approaches described above respond to the same set of events. The names of the built-in events are listed below. (The hash of built-in events exists in Ember.EventDispatcher
.) Additional, custom events can be registered by using Ember.Application.customEvents
.
Touch events:
touchStart
touchMove
touchEnd
touchCancel
Keyboard events:
keyDown
keyUp
keyPress
Mouse events:
mouseDown
mouseUp
contextMenu
click
doubleClick
mouseMove
focusIn
focusOut
mouseEnter
mouseLeave
Form events:
submit
change
focusIn
focusOut
input
HTML5 drag and drop events:
dragStart
drag
dragEnter
dragLeave
dragOver
dragEnd
drop
$ (selector) JQuery
public
Returns a jQuery object for this component's element. If you pass in a selector string, this method will return a jQuery object, using the current element as its buffer. For example, calling component.$('li')
will return a jQuery object containing all of the li
elements inside the DOM element of this component.
Parameters:
-
selector
[String]
- a jQuery-compatible selector string
Returns:
-
JQuery
- the jQuery object for the DOM node
destroyprivate
You must call destroy
on a view to destroy the view (and all of its child views). This will remove the view from any parent node, then make sure that the DOM element managed by the view can be released by the memory manager.
didReceiveAttrspublic
Called when the attributes passed into the component have been updated. Called both during the initial render of a container and during a rerender. Can be used in place of an observer; code placed here will be executed every time any attribute updates.
didRenderpublic
Called after a component has been rendered, both on initial render and in subsequent rerenders.
didUpdatepublic
Called when the component has updated and rerendered itself. Called only during a rerender, not during an initial render.
didUpdateAttrspublic
Called when the attributes passed into the component have been changed. Called only during a rerender, not during an initial render.
initprivate
Setup a view, but do not finish waking it up.
- configure
childViews
- register the view with the global views hash, which is used for event dispatch
readDOMAttr (name) public
Normally, Ember's component model is "write-only". The component takes a bunch of attributes that it got passed in, and uses them to render its template.
One nice thing about this model is that if you try to set a value to the same thing as last time, Ember (through HTMLBars) will avoid doing any work on the DOM.
This is not just a performance optimization. If an attribute has not changed, it is important not to clobber the element's "hidden state". For example, if you set an input's value
to the same value as before, it will clobber selection state and cursor position. In other words, setting an attribute is not always idempotent.
This method provides a way to read an element's attribute and also update the last value Ember knows about at the same time. This makes setting an attribute idempotent.
In particular, what this means is that if you get an <input>
element's value
attribute and then re-render the template with the same value, it will avoid clobbering the cursor and selection position. Since most attribute sets are idempotent in the browser, you typically can get away with reading attributes using jQuery, but the most reliable way to do so is through this method.
Parameters:
-
name
String
- the name of the attribute
Returns:
- String
willRenderpublic
Called before a component has been rendered, both on initial render and in subsequent rerenders.
willUpdatepublic
Called when the component is about to update and rerender itself. Called only during a rerender, not during an initial render.
didReceiveAttrspublic
Called when the attributes passed into the component have been updated. Called both during the initial render of a container and during a rerender. Can be used in place of an observer; code placed here will be executed every time any attribute updates.
didRenderpublic
Called after a component has been rendered, both on initial render and in subsequent rerenders.
didUpdatepublic
Called when the component has updated and rerendered itself. Called only during a rerender, not during an initial render.
didUpdateAttrspublic
Called when the attributes passed into the component have been changed. Called only during a rerender, not during an initial render.
willRenderpublic
Called before a component has been rendered, both on initial render and in subsequent rerenders.
willUpdatepublic
Called when the component is about to update and rerender itself. Called only during a rerender, not during an initial render.
ariaRoleString
public
The WAI-ARIA role of the control represented by this view. For example, a button may have a role of type 'button', or a pane may have a role of type 'alertdialog'. This property is used by assistive software to help visually challenged users navigate rich web applications.
The full list of valid WAI-ARIA roles is available at: http://www.w3.org/TR/wai-aria/roles#roles_categorization
Default: null
elementIdString
public
The HTML id
of the component's element in the DOM. You can provide this value yourself but it must be unique (just as in HTML):
{{my-component elementId="a-really-cool-id"}}
If not manually set a default value will be provided by the framework. Once rendered an element's elementId
is considered immutable and you should never change it. If you need to compute a dynamic value for the elementId
, you should do this when the component or element is being instantiated:
export default Ember.Component.extend({ init() { this._super(...arguments); var index = this.get('index'); this.set('elementId', `component-id${index}`); } });
isVisibleBoolean
public
If false
, the view will appear hidden in DOM.
Default: null
layoutFunction
public
A component may contain a layout. A layout is a regular template but supersedes the template
property during rendering. It is the responsibility of the layout template to retrieve the template
property from the component (or alternatively, call Handlebars.helpers.yield
, {{yield}}
) to render it in the correct location. This is useful for a component that has a shared wrapper, but which delegates the rendering of the contents of the wrapper to the template
property on a subclass.
layoutNameString
private
The name of the layout to lookup if no layout is provided. By default Ember.Component
will lookup a template with this name in Ember.TEMPLATES
(a shared global object).
Default: null
positionalParamspublicstatic
Enables components to take a list of parameters as arguments. For example, a component that takes two parameters with the names name
and age
:
let MyComponent = Ember.Component.extend; MyComponent.reopenClass({ positionalParams: ['name', 'age'] });
It can then be invoked like this:
{{my-component "John" 38}}
The parameters can be referred to just like named parameters:
Name: {{name}}, Age: {{age}}.
Using a string instead of an array allows for an arbitrary number of parameters:
let MyComponent = Ember.Component.extend; MyComponent.reopenClass({ positionalParams: 'names' });
It can then be invoked like this:
{{my-component "John" "Michael" "Scott"}}
The parameters can then be referred to by enumerating over the list:
{{#each names as |name|}}{{name}}{{/each}}
© 2017 Yehuda Katz, Tom Dale and Ember.js contributors
Licensed under the MIT License.
https://emberjs.com/api/classes/Ember.Component.html