Using JavaScript and DOM APIs

Since A-Frame is just HTML, we can control the scene and its entities using JavaScript and DOM APIs as we mostly would in ordinary web development.

With JavaScript Image by Ruben Mueller from The VR Jump.

Every element in the scene, even elements such as <a-box> or <a-sky>, are entities (represented as <a-entity>). A-Frame modifies the HTML element prototype to add some extra behavior for certain DOM APIs to tailor them to A-Frame. See the Entity API documentation for reference on most of the APIs discussed below.

Table of Contents

Where to Place JavaScript Code for A-Frame

Before we go over the different ways to use JavaScript and DOM APIs, we recommend encapsulating your JavaScript code within A-Frame components. Components modularize code, make logic and behavior visible from HTML, and ensure that code at the correct time (e.g., after the scene and entities have attached and initialized). As the most basic example, to register a console.log component:

AFRAME.registerComponent('log', {
schema: {type: 'string'},
init: function () {
var stringToLog = this.data;
console.log(stringToLog);
}
});

Then to use the component from HTML:

<a-scene log="Hello, Scene!">
<a-box log="Hello, Box!"></a-box>
</a-scene>

Components encapsulate all of our code to be reusable, declarative, and shareable. Though if we’re just poking around at runtime, we can use our browser’s Developer Tools Console to run JavaScript on our scene.

Getting Entities by Querying and Traversing

The wonderful thing about the DOM as a scene graph is that the standard DOM provides utilities for traversal, querying, finding, and selecting through .querySelector() and .querySelectorAll(). Originally inspired by jQuery selectors, we can learn about query selectors on MDN.

Let’s run a few example query selectors. Take the scene below for example.

<html>
<a-scene>
<a-box id="redBox" class="clickable" color="red"></a-box>
<a-sphere class="clickable" color="blue"></a-sphere>
<a-box color="green"></a-box>
<a-entity light="type: ambient"></a-entity>
<a-entity light="type: directional"></a-entity>
</a-scene>
</html>

With .querySelector()

If we want to grab just one element, we use .querySelector() which returns one element. Let’s grab the scene element:

var sceneEl = document.querySelector('a-scene');

Note if we were working within a component, we’d already have a reference to the scene element without needing to query. All entities have reference to their scene element:

AFRAME.registerComponent('foo', {
init: function () {
console.log(this.el.sceneEl); // Reference to the scene element.
}
});

If an element has an ID, we can use an ID selector (i.e., #<ID>). Let’s grab the red box which has an ID. Before we did a query selector on the entire document. Here, we’ll do a query selector just within the scope of the scene. With query selectors, we’re able to limit to scope of the query to within any element:

var sceneEl = document.querySelector('a-scene');
console.log(sceneEl.querySelector('#redBox'));
// <a-box id="redBox" class="clickable" color="red"></a-box>

With .querySelectorAll()

If we want to grab a group of elements, we use .querySelectorAll() which returns an array of elements. We can query across element names:

console.log(sceneEl.querySelectorAll('a-box'));
// [
// <a-box id="redBox" class="clickable" color="red"></a-box>,
// <a-box color="green"></a-box>
// ]

We can query for elements that have a class with a class selector (i.e., .<CLASS_NAME>). Let’s grab every entity that has the clickable class:

console.log(sceneEl.querySelectorAll('.clickable'));
// [
// <a-box id="redBox" class="clickable" color="red"></a-box>
// <a-sphere class="clickable" color="blue"></a-sphere>
// ]

We can query for elements containing an attribute (or in this case, a component) with an attribute selector (i.e., [<ATTRIBUTE_NAME>]). Let’s grab every entity that has a light:

console.log(sceneEl.querySelectorAll('[light]'));
// [
// <a-entity light="type: ambient"></a-entity>
// <a-entity light="type: directional"></a-entity>
// ]

Looping Over Entities from .querySelectorAll()

If we grabbed a group of entities using .querySelectorAll(), we can loop over them with a for loop. Let’s loop over every element in the scene with *.

var els = sceneEl.querySelectorAll('*');
for (var i = 0; i < els.length; i++) {
console.log(els[i]);
}

Modifying the A-Frame Scene Graph

With JavaScript and DOM APIs, we can dynamically add and remove entities as we would with normal HTML elements.

Creating an Entity with .createElement()

To create an entity, we can use document.createElement. This will give us a blank entity:

var el = document.createElement('a-entity');

However, this entity will not be initialized or be a part of the scene until we attach it to our scene.

Adding an Entity with .appendChild()

To add an entity to the DOM, we can use .appendChild(element). Specifically, we want to add it to our scene. We grab the scene, create the entity, and append the entity to our scene.

var sceneEl = document.querySelector('a-scene');
var entityEl = document.createElement('a-entity');
// Do `.setAttribute()`s to initialize the entity.
sceneEl.appendChild(entityEl);

Note that .appendChild() is an asynchronous operation in the browser. Until the entity has finished appending to the DOM, we can’t do many operations on the entity (such as calling .getAttribute()). If we need to query an attribute on an entity that has just been appended, we can listen to the loaded event on the entity, or place logic in an A-Frame component so that it is executed once it is ready:

var sceneEl = document.querySelector('a-scene');
AFRAME.registerComponent('do-something-once-loaded', {
init: function () {
// This will be called after the entity has properly attached and loaded.
console.log('I am ready'!);
}
});
var entityEl = document.createElement('a-entity');
entityEl.setAttribute('do-something-once-loaded', '');
sceneEl.appendChild(entityEl);

Removing an Entity with .removeChild()

To remove an entity from the DOM and thus from the scene, we call .removeChild(element) from the parent element. If we have an entity, we have to ask its parent (parentNode) to remove the entity.

entityEl.parentNode.removeChild(entityEl);

Modifying an Entity

A blank entity doesn’t do anything. We can modify the entity by adding components, configuring component properties, and removing components.

Adding a Component with .setAttribute()

To add a component, we can use .setAttribute(componentName, data). Let’s add a geometry component to the entity.

entityEl.setAttribute('geometry', {
primitive: 'box',
height: 3,
width: 1
});

Or adding the community physics component:

entityEl.setAttribute('dynamic-body', {
shape: 'box',
mass: 1.5,
linearDamping: 0.005
});

Unlike a normal HTML .setAttribute(), an entity’s .setAttribute() is improved to take a variety of types of arguments such as objects, or to be able to update a single property of a component. Read more about Entity.setAttribute().

Updating a Component with .setAttribute()

To update a component, we also use .setAttribute(). Updating a component takes several forms.

Updating Property of Single-Property Component

Let’s update the property of the position component, a single-property component. We can pass either an object or a string. It is slightly preferred to pass an object so A-Frame doesn’t have to parse the string.

entityEl.setAttribute('position', {x: 1, y: 2: z: -3});
// Or entityEl.setAttribute('position', '1 2 -3');

Updating Single Property of Multi-Property Component

Let’s update a single property of the material component, a multi-property component. We do this by providing the component name, property name, and then property value to .setAttribute():

entityEl.setAttribute('material', 'color', 'red');

Updating Multiple Properties of a Multi-Property Component

Let’s update multiple properties at once of the light component, a multi-property component. We do this by providing the component name and an object of properties to .setAttribute(). We’ll change the light’s color and intensity but leave the type the same:

// <a-entity light="type: directional; color: #CAC; intensity: 0.5"></a-entity>
entityEl.setAttribute('light', {color: '#ACC', intensity: 0.75});
// <a-entity light="type: directional; color: #ACC; intensity: 0.75"></a-entity>

Replacing Properties of a Multi-Property Component

Let’s replace all the properties of the geometry component, a multi-property component. We do this by providing the component name, an object of properties to .setAttribute(), and a flag that specifies to clobber the existing properties. We’ll replace all of the geometry’s existing properties with new properties:

// <a-entity geometry="primitive: cylinder; height: 4; radius: 2"></a-entity>
entityEl.setAttribute('geometry', {primitive: 'torusKnot', p: 1, q: 3, radiusTubular: 4}, true);
// <a-entity geometry="primitive: torusKnot; p: 1; q: 3; radiusTubular: 4"></a-entity>

Removing a Component with .removeAttribute()

To remove or detach a component from an entity, we can use .removeAttribute(componentName). Let’s remove the default wasd-controls from the camera entity:

var cameraEl = document.querySelector('[camera]');
cameraEl.removeAttribute('wasd-controls');

Events and Event Listeners

With JavaScript and the DOM, there is an easy way for entities and components to communicate with one another: events and event listeners. Events are a way to send out a signal that other code can pick up and respond to. Read more about browser events.

Emitting an Event with .emit()

A-Frame elements provide an easy way to emit custom events with .emit(eventName, eventDetail, bubbles). For example, let’s say we are building a physics component and we want the entity to send out a signal when it has collided with another entity:

entityEl.emit('physicscollided', {collidingEntity: anotherEntityEl}, false);

Then other parts of the code can wait and listen on this event and run code in response. We can pass information and data through the event detail as the second argument. And we can specify whether the event bubbles, meaning that the parent entities will also emit the event. So other parts of the code can register an event listener.

Adding an Event Listener with .addEventListener()

Like with normal HTML elements, we can register an event listener with .addEventListener(eventName, function). When the event the listener is registered to is emitted, then the function will be called and handle the event. For example, continuing from the previous example with the physics collision event:

entityEl.addEventListener('physicscollided', function (event) {
console.log('Entity collided with', event.detail.collidingEntity);
});

When the entity emits the physicscollided event, the function will be called with the event object. Notably in the event object, we have the event detail which contains data and information passed through the event.

Removing an Event Listener with .removeEventListener()

Like with normal HTML elements, when we want to remove the event listener, we can use .removeEventListener(eventName, function). We have to pass the same event name and function that the listener was registered with. For example, continuing from the previous example with the physics collision event:

// We have to define this function with a name if we later remove it.
function collisionHandler (event) {
console.log('Entity collided with', event.detail.collidingEntity);
});
entityEl.addEventListener('physicscollided', collisionHandler);
entityEl.removeEventListener('physicscollided', collisionHandler);