Entity

Note: This documentation is for the old 0.4.0 version of A-Frame. Check out the documentation for the current 1.7.0 version

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A-Frame represents an entity via the <a-entity> element. As defined in the entity-component-system pattern, entities are placeholder objects to which we plug in components to provide them appearance, behavior, and functionality.

In A-Frame, entities are inherently attached with the position, rotation, and scale components.

Example

Consider the entity below. By itself, it has no appearance, behavior, or functionality. It does nothing:

<a-entity>

We can attach components to it to make it render something or do something. To give it shape and appearance, we can attach the geometry and material components:

<a-entity geometry="primitive: box" material="color: red">

Or to make it emit light, we can further attach the light component:

<a-entity geometry="primitive: box" material="color: red"
          light="type: point; intensity: 2.0">

Retrieving an Entity

We can simply retrieve an entity using DOM APIs.

<a-entity id="mario"></a-entity>

var el = document.querySelector('#mario');

Once we have an entity, we have access to its properties and methods detailed below.

Properties

components

<a-entity>.components is an object of components attached to the entity. This gives us access to the entity’s components including each component’s data, state, and methods.

For example, if we wanted to grab an entity’s three.js camera object or material object, we could reach into its components:

var camera = document.querySelector('a-entity[camera]').components.camera.camera;
var material = document.querySelector('a-entity[material]').components.material.material;

Or if a component exposes an API, we can call its methods:

document.querySelector('a-entity[sound]').components.sound.pause();

isPlaying

Whether the entity is active and playing. If we pause the entity , then isPlaying becomes false.

object3D

<a-entity>.object3D is a reference to the entity’s three.js Object3D representation. More specifically, object3D will be a THREE.Group object that may contain different types of THREE.Object3Ds such as cameras, meshes, lights, or sounds:

// Gaining access to the internal three.js scene graph.
var groupObject3D = document.querySelector('a-entity').object3D;
console.log(groupObject3D.parent);
console.log(groupObject3D.children);

We can access the different types of Object3Ds through object3DMap.

object3DMap

An entity’s object3DMap is an object that gives access to the different types of THREE.Object3Ds (e.g., camera, meshes, lights, sounds) that components have set.

For an entity with a geometry and light components attached, object3DMap might look like:

{
  light: <THREE.Light Object>,
  mesh: <THREE.Mesh Object>
}

We can manage an entity’s set of THREE.Object3Ds by using getOrCreateObject3D, setObject3D, and removeObject3D.

sceneEl

An entity has a reference to its scene element.

var sceneEl = document.querySelector('a-scene');
var entity = sceneEl.querySelector('a-entity');
console.log(entity.sceneEl === sceneEl);  // >> true.

Methods

addState (stateName)

addState will push a state onto the entity. This will emit the stateadded event, and we can check the state can for existence using .is:

entity.addEventListener('stateadded', function (evt) {
  if (evt.detail.state === 'selected') {
    console.log('Entity now selected!');
  }
});

entity.addState('selected');
entity.is('selected');  // >> true

emit (name, detail, bubbles)

emit emits a custom DOM event on the entity. For example, we can emit an event to trigger an animation:

// <a-entity>
//   <a-animation attribute="rotation" begin="rotate" to="0 360 0"></a-animation>
// </a-entity>
entity.emit('rotate');

We can also pass event detail or data as the second argument:

entity.emit('collide', { target: collidingEntity });

The event will bubble by default. we can tell it not to bubble by passing false for bubble:

entity.emit('sink', null, false);

flushToDOM (recursive)

flushToDOM will manually serialize an entity’s components’ data and update the DOM. Read more about component-to-DOM serialization.

getAttribute (componentName)

getAttribute retrieves parsed component data (including mixins and defaults).

// <a-entity geometry="primitive: box; width: 3">

entity.getAttribute('geometry');
// >> {primitive: "box", depth: 2, height: 2, translate: "0 0 0", width: 3, ...}

entity.getAttribute('geometry').primitive;
// >> "box"

entity.getAttribute('geometry').height;
// >> 2

entity.getAttribute('position');
// >> {x: 0, y: 0, z: 0}

If componentName is not the name of a registered component, getAttribute will behave as it normally would:

// <a-entity data-position="0 1 1">

entity.getAttribute('data-position');
// >> "0 1 1"

getDOMAttribute (componentName)

getDOMAttribute retrieves only parsed component data that is explicitly defined in the DOM or via setAttribute. If componentName is the name of a registered component, getDOMAttribute will return only the component data defined in the HTML as a parsed object. getDOMAttribute for components is the partial form of getAttribute since the returned component data does not include applied mixins or default values:

Compare the output of the above example of getAttribute:

// <a-entity geometry="primitive: box; width: 3">

entity.getDOMAttribute('geometry');
// >> { primitive: "box", width: 3 }

entity.getDOMAttribute('geometry').primitive;
// >> "box"

entity.getDOMAttribute('geometry').height;
// >> undefined

entity.getDOMAttribute('position');
// >> undefined

getObject3D (type)

getObject3D looks up a child THREE.Object3D referenced by type on object3DMap.

AFRAME.registerComponent('example-mesh', {
  init: function () {
    var el = this.el;
    el.getOrCreateObject3D('mesh', THREE.Mesh);
    el.getObject3D('mesh');  // Returns THREE.Mesh that was just created.
  }
});

getOrCreateObject3D (type, Constructor)

If the entity does not have a THREE.Object3D registered under type, getOrCreateObject3D will register an instantiated THREE.Object3D using the passed Constructor. If the entity does have an THREE.Object3D registered under type, getOrCreateObject3D will act as getObject3D:

AFRAME.registerComponent('example-geometry', {
  update: function () {
    var mesh = this.el.getOrCreateObject3D('mesh', THREE.Mesh);
    mesh.geometry = new THREE.Geometry();
  }
});

pause ()

pause() will stop any dynamic behavior as defined by animations and components. When we pause an entity, it will stop its animations and call Component.pause() on each of its components. The components decide to implement what happens on pause, which is often removing event listeners. An entity will call pause() on its child entities when we pause an entity.

// <a-entity id="spinning-jumping-ball">
entity.pause();

For example, the look-controls component on pause will remove event handlers that listen for input.

play ()

play() will start any dynamic behavior as defined by animations and components. This is automatically called when the DOM attaches an entity. When an entity play(), the entity calls play() on its child entities.

entity.pause();
entity.play();

For example, the sound component on play will begin playing the sound.

setAttribute (attr, value, componentAttrValue)

If attr is not the name of a registered component or the component is a single-property component, setAttribute behaves as it normally would:

entity.setAttribute('visible', false);

Though if attr is the name of a registered component, it may handle special parsing for the value. For example, the position component is a single-property component, but its property type parser allows it to take an object:

entity.setAttribute('position', { x: 1, y: 2, z: 3 });

Putting Multi-Property Component Data

To set or replace component data for a multi-property component, we can pass the name of a registered component as the attr, and pass an object of properties as the value:

// All previous properties for the light component will be removed and overwritten.
entity.setAttribute('light', {
  type: 'spot',
  distance: 30,
  intensity: 2.0
});

Updating Multi-Property Component Data

To update individual properties for a multi-property component, we can pass the name of registered component as the attr, a property name as the second argument, and the property value to set as the third argument:

// All previous properties for the material component (besides the color)  will be unaffected.
entity.setAttribute('material', 'color', 'crimson');

setObject3D (type, obj)

setObject3D will register the passed obj, a THREE.Object3D, as type under the entity’s object3DMap. A-Frame adds obj as a child of the entity’s root object3D.

AFRAME.registerComponent('example-orthogonal-camera', {
  update: function () {
    this.el.setObject3D('camera', new THREE.OrthogonalCamera());
  }
});

removeAttribute (attr)

If attr is the name of a registered component, along with removing the attribute from the DOM, removeAttribute will also detach the component from the entity, invoking the component’s remove lifecycle method.

entity.removeAttribute('sound');  // The entity will no longer play sound.

removeObject3D (type)

removeObject3D removes the object specified by type from the entity’s THREE.Group and thus from the scene. This will update the entity’s object3DMap, setting the value of the type key to null. This is generally called from a component, often within the remove handler:

AFRAME.registerComponent('example-light', {
  update: function () {
    this.el.setObject3D('light', new THREE.Light());
    // Light is now part of the scene.
    // object3DMap.light is now a THREE.Light() object.
  },

  remove: function () {
    this.el.removeObject3D('light');
    // Light is now removed from the scene.
    // object3DMap.light is now null.
  }
});

removeState (stateName)

removeState will pop a state from the entity. This will emit the stateremoved event, and we can check the state its removal using .is:

entity.addEventListener('stateremoved', function (evt) {
  if (evt.detail.state === 'selected') {
    console.log('Entity no longer selected.');
  }
});

entity.addState('selected');
entity.is('selected');  // >> true

entity.removeState('selected');
entity.is('selected');  // >> false

Events

Event Detail

Below is what the event detail contains for each event:

Listening for Component Changes

We can use the componentchanged event to listen for changes to the entity:

entity.addEventListener('componentchanged', function (evt) {
  if (evt.detail.name === 'position') {
    console.log('Entity has moved from', evt.detail.oldData, 'to', evt.detail.newData, '!');
  }
});

Listening for Child Elements Being Attached and Detached

We can use the child-attached and child-detached events to listen for when the scene attaches or detaches an entity:

entity.addEventListener('child-attached', function (evt) {
  if (evt.detail.el.tagName.toLowerCase() === 'a-box') {
    console.log('a box element has been attached');
  };
});