If you are new to scripting we recommend reading the following guides first:

Sometimes it can also be helpful to dive into the Needle Engine Api documentationopen in new window.

Runtime code for Needle Engine is written in TypeScriptopen in new window (recommended) or JavaScriptopen in new window. We automatically generate C# stub components out of that, which you can add to GameObjects in the editor. The C# components and their data are recreated by the runtime as JavaScript components with the same data and attached to three.js objects.

Both custom components as well as built-in Unity components can be mapped to JavaScript components in this way. For example, mappings for many built-in components related to animation, rendering or physics are already included in Needle Engine.

If you want to code-along with the following examples without having to install anything you just click the following link:

Our web runtime engine adopts a component model similar to Unity and thus provides a lot of functionality that will feel familiar. Components attached to three's Object3D objects have lifecycle methods like awake, start, onEnable, onDisable, update and lateUpdate that you can implement. You can also use Coroutines.

When you don't need to write code

Often, interactive scenes can be realized using Events in Unity and calling methods on built-in components. A typical example is playing an animation on button click - you create a button, add a Click event in the inspector, and have that call Animator.SetTrigger or similar to play a specific animation.

Needle Engine translates Unity Events into JavaScript method calls, which makes this a very fast and flexible workflow - set up your events as usual and when they're called they'll work the same as in Unity.

An example of a Button Click Event that is working out-of-the-box in Needle Engine — no code needed.

Creating a new component

Scripts are written in TypeScript (recommended) or JavaScript.
There are two ways to add custom scripts to your project:

  • Simply add a file with an .ts or .js extension inside src/scripts/ in your generated project directory, for example src/scripts/MyFirstScript.ts

  • Unity specific:
    Organize your code into NPM Definition Files (npm packages). These help you to modularize and re-use code between projects and if you are familiar with web development they are in fact regular npm packages that are installed locally.
    In Unity you can create NpmDef files via Create > NPM Definition and then add TypeScript files by right-clicking an NpmDef file and selecting Create > TypeScript. Please see this chapter for more information.

In both approaches, source directories are watched for changes and C# stub components or Blender panels are regenerated whenever a change is detected.
Changes to the source files also result in a hot reload of the running website – you don't have to wait for Unity to recompile the C# components. This makes iterating on code pretty much instant.

You can even have multiple component types inside one file (e.g. you can declare export class MyComponent1 and export class MyOtherComponent in the same Typescript file).

If you are new to writing Javascript or Typescript we recommend reading the Typescript Essentials Guide guide first before continuing with this guide.

Example: Creating a Component that rotates an object
  • Create a component that rotates an object
    Create src/scripts/Rotate.ts and add the following code:
import { Behaviour, serializable } from "@needle-tools/engine";

export class Rotate extends Behaviour
    speed : number = 1;

        // logging this is useful for debugging in the browser. 
        // You can open the developer console (F12) to see what data your component contains

    // update will be called every frame
        this.gameObject.rotateY(this.context.time.deltaTime * this.speed);

Now inside Unity a new script called Rotate.cs will be automatically generated. Add the new Unity component to a Cube and save the scene.
The cube is now rotating inside the browser.
Open the chrome developer console by F12 to inspect the log from the Rotate.start method. This is a helpful practice to learn and debug what fields are exported and currently assigned. In general all public and serializable fields and all public properties are exported.

Now add a new field public float speed = 5 to your Unity component and save it. The Rotate component inspector now shows a speed field that you can edit. Save the scene (or click the Build button) and note that the javascript component now has the exported speed value assigned.

Create component with a custom function

Refer to the Typescript Essentials Guide to learn more about the syntax and language.

import { Behaviour } from "@needle-tools/engine";

export class PrintNumberComponent extends Behaviour
    private printNumber(myNumber : number){
        console.log("My Number is: " + myNumber);
Version Control & Unity

While generated C# components use the type name to produce stable GUIDs, we recommend checking in generated components in version control as a good practice.

Component architecture

Components are added to three.js Object3Ds. This is similar to how Components in Unity are added to GameObjects. Therefore when we want to access a three.js Object3D, we can access it as this.gameObject which returns the Object3D that the component is attached to.

Note: Setting visible to false on a Object3D will act like SetActive(false) in Unity - meaning it will also disable all the current components on this object and its children. Update events for inactive components are not being called until visible is set to true again. If you want to hide an object without affecting components you can just disable the Needle Engine Renderer component.

Lifecycle methods

Note that lifecycle methods are only being called when they are declared. So only declare update lifecycle methods when they are actually necessary, otherwise it may hurt performance if you have many components with update loops that do nothing.

Method nameDescription
awake()First method being called when a new component is created
onEnable()Called when a component is enabled (e.g. when enabled changes from false to true)
onDisable()Called when a component is disabled (e.g. when enabled changes from true to false)
onDestroy()called when the Object3D or component is being destroyed
start()Called on the start of the first frame after the component was created
earlyUpdate()First update event
update()Default update event
lateUpdate()Called after update
onBeforeRender()Last update event before render call
onAfterRender()Called after render event

Physic event methods

Method nameDescription
onCollisionEnter(col : Collision)
onCollisionStay(col : Collision)
onCollisionExit(col : Collision)
onTriggerEnter(col : Collision)
onTriggerStay(col : Collision)
onTriggerExit(col : Collision)

Input event methods

Method nameDescription
onPointerEnter(args : PointerEventData)Called when a cursor starts to hover over an object (or any of it's children)
onPointerMove(args : PointerEventData)Called when a cursor moves over an object (or any of it's children)
onPointerExit(args : PointerEventData)Called when a cursor exists (stops hovering) an object
onPointerDown(args : PointerEventData)Called when a cursor is pressed over an object
onPointerUp(args : PointerEventData)Called when a cursor is released over an object
onPointerClick(args : PointerEventData)Called when a cursor is clicked over an object

XR event methods

requires Needle Engine >= 3.32.0

Method nameDescription
supportsXR(mode: XRSessionMode)Optionally implement if you only want to receive XR callbacks for specific XR modes like immersive-vr or immersive-ar. Return true to notify the system that you want callbacks for the passed in mode
onBeforeXR(mode: XRSessionMode, init: XRSessionInit)Called right before a XRSession is requested and can be used to modify the XRSessionInit object
onEnterXR(args: NeedleXREventArgs)Callback when this component joins a xr session (or becomes active in a running XR session)
onUpdateXR(args: NeedleXREventArgs)Callback when a xr session updates (while it is still active in XR session)
onLeaveXR(args: NeedleXREventArgs)allback when this component exists a xr session (or when it becomes inactive in a running XR session)
onControllerAdded(args: NeedleXRControllerEventArgs)Callback when a controller is connected/added while in a XR session OR when the component joins a running XR session that has already connected controllers OR when the component becomes active during a running XR session that has already connected controllers
onControllerRemoved(args: NeedleXRControllerEventArgs)callback when a controller is removed while in a XR session OR when the component becomes inactive during a running XR session

Additional XR events

Method nameDescription
window.addEventListener("needle-xrsession-start")CustomEvent that is invoked when a XRSession starts. details contains the NeedleXRSession
window.addEventListener("needle-xrsession-end")CustomEvent that is invoked when a XRSession starts. details contains the NeedleXRSession
onXRSessionStart(args: { session:NeedleXRSession } )global event hook. To unsubscribe use offXRSessionStart


Coroutines can be declared using the JavaScript Generator Syntaxopen in new window.
To start a coroutine, call this.startCoroutine(this.myRoutineName());


import { Behaviour, FrameEvent } from "@needle-tools/engine";

export class Rotate extends Behaviour {

    start() {
        // the second argument is optional and allows you to specifiy 
        // when it should be called in the current frame loop
        // coroutine events are called after regular component events of the same name
        // for example: Update coroutine events are called after component.update() functions
        this.startCoroutine(this.rotate(), FrameEvent.Update);

    // this method is called every frame until the component is disabled
    *rotate() {
        // keep looping forever
        while (true) {

To stop a coroutine, either exit the routine by returning from it, or cache the return value of startCoroutine and call this.stopCoroutine(<...>). All Coroutines are stopped at onDisable / when disabling a component.

Special Lifecycle hooks

Needle Engine also exposes a few lifecycle hooks that you can use to hook into the update loop without having to write a full component.
Those hooks can be inserted at any point in your web application (for example in toplevel scope or in a svelte component)

Method nameDescription
onInitialized(cb, options)Called when a new context is initialized (before the first frame)
onClear(cb, options)Register a callback before the engine context is cleared
onDestroy(cb, options)Register a callback in the engine before the context is destroyed
onStart(cb, options)Called directly after components start at the beginning of a frame
onUpdate(cb, options)Called directly after components update
onBeforeRender(cb, options)called before calling render
onAfterRender(cb, options)called before calling render

For example (See example on stackblitzopen in new window)

// this can be put into e.g. main.ts or a svelte component (similar to onMount)
import { onUpdate, onBeforeRender } from "@needle-tools/engine"
onUpdate((ctx: Context) => {
    // do something... e.g. access the scene via ctx.scene
    console.log("UPDATE", ctx.time.frame);

onBeforeRender((ctx: Context) => {
    // this event is only called once because of the { once: true } argument
    console.log("ON BEFORE RENDER", ctx.time.frame);
}, { once: true } );

// Every event hook returns a method to unsubscribe from the event
const unsubscribe = onAfterRender((ctx: Context) => {
    console.log("ON AFTER RENDER", ctx.time.frame);
// Unsubscribe from the event at any time
setTimeout(()=> unsubscribe(), 1000);

Finding, adding and removing components

To access other components, use the static methods on GameObject or this.gameObject methods. For example, to access a Renderer component in the parent use GameObject.getComponentInParent(this.gameObject, Renderer) or this.gameObject.getComponentInParent(Renderer).


import { Behaviour, GameObject, Renderer } from "@needle-tools/engine";

export class MyComponent extends Behaviour {

    start() {
        const renderer = GameObject.getComponentInParent(this.gameObject, Renderer);

Some of the available methods:

GameObject.instantiate(Object3D, InstantiateOptions)creates a new instance of this object including new instances of all its components
GameObject.destroy(Object3D | Component)destroy a component or Object3D (and its components)
GameObject.addNewComponent(Object3D, Type)adds (and creates) a new component for a type to the provided object. Note that awake and onEnable is already called when the component is returned
GameObject.addComponent(Object3D, Component)moves a component instance to the provided object. It is useful if you already have an instance e.g. when you create a component with e.g. new MyComponent() and then attach it to a object
GameObject.removeComponent(Component)removes a component from a gameObject
GameObject.getComponent(Object3D, Type)returns the first component matching a type on the provided object.
GameObject.getComponents(Object3D, Type)returns all components matching a type on the provided object.
GameObject.getComponentInChildrensame as getComponent but also searches in child objects.
GameObject.getComponentsInChildrensame as getComponents but also searches in child objects.
GameObject.getComponentInParentsame as getComponent but also searches in parent objects.
GameObject.getComponentsInParentsame as getComponents but also searches in parent objects.
GameObject.findObjectOfTypesearches the whole scene for a type.
GameObject.findObjectsOfTypesearches the whole scene for all matching types.

Three.js and the HTML DOM

The context refers to the runtime inside a web componentopen in new window.
The three.js scene lives inside a custom HTML component called <needle-engine> (see the index.html in your project). You can access the <needle-engine> web component using this.context.domElement.

This architecture allows for potentially having multiple needle WebGL scenes on the same webpage, that can either run on their own or communicate between each other as parts of your webpage.

Access the scene

To access the current scene from a component you use this.scene which is equivalent to this.context.scene, this gives you the root three.js scene object.

To traverse the hierarchy from a component you can either iterate over the children of an object
with a for loop:

for(let i = 0; i < this.gameObject.children; i++) 
    const ch = this.gameObject.children[i];

or you can iterate using the foreach equivalent:

for(const child of this.gameObject.children) {

You can also use three.js specific methods to quickly iterate all objects recursively using the traverseopen in new window method:

this.gameObject.traverse(obj => console.log(obj))

or to just traverse visible objects use traverseVisibleopen in new window instead.

Another option that is quite useful when you just want to iterate objects being renderable you can query all renderer components and iterate over them like so:

for(const renderer of this.gameObject.getComponentsInChildren(Renderer))

For more information about getting components see the next section.


Use this.context.time to get access to time data:

  • this.context.time.time is the time since the application started running
  • this.context.time.deltaTime is the time that has passed since the last frame
  • this.context.time.frameCount is the number of frames that have passed since the application started
  • this.context.time.realtimeSinceStartup is the unscaled time since the application has started running

It is also possible to use this.context.time.timeScale to deliberately slow down time for e.g. slow motion effects.


Use this.context.input to poll input state:

import { Behaviour } from "@needle-tools/engine";
export class MyScript extends Behaviour
            console.log("POINTER DOWN")

You can also subscribe to events in the InputEvents enum like so:

import { Behaviour, InputEvents } from "@needle-tools/engine";

export class MyScript extends Behaviour
        this.context.input.addEventListener(InputEvents.PointerDown, this.onPointerDown);
    onDisable() {
        // it is recommended to also unsubscribe from events when your component becomes inactive
        this.context.input.removeEventListener(InputEvents.PointerDown, this.onPointerDown);

    private onPointerDown = (evt) => { console.log(evt); }

If you want to handle inputs yourself you can also subscribe to all events the browser providesopen in new window (there are a ton). For example to subscribe to the browsers click event you can write:

window.addEventListener("click", () => { console.log("MOUSE CLICK"); });

Note that in this case you have to handle all cases yourself. For example you may need to use different events if your user is visiting your website on desktop vs mobile vs a VR device. These cases are automatically handled by the Needle Engine input events (e.g. PointerDown is raised both for mouse down, touch down and in case of VR on controller button down).


Use this.context.physics.raycast() to perform a raycast and get a list of intersections. If you dont pass in any options the raycast is performed from the mouse position (or first touch position) in screenspace using the currently active mainCamera. You can also pass in a RaycastOptions object that has various settings like maxDistance, the camera to be used or the layers to be tested against.

Use this.context.physics.raycastFromRay(your_ray) to perform a raycast using a three.js rayopen in new window

Note that the calls above are by default raycasting against visible scene objects. That is different to Unity where you always need colliders to hit objects. The default three.js solution has both pros and cons where one major con is that it can perform quite slow depending on your scene geometry. It may be especially slow when raycasting against skinned meshes. It is therefor recommended to usually set objects with SkinnedMeshRenderers in Unity to the Ignore Raycast layer which will then be ignored by default by Needle Engine as well.

Another option is to use the physics raycast methods which will only return hits with colliders in the scene.

const hit = this.context.physics.engine?.raycast();

Here is a editable example for physics raycastopen in new window


Networking methods can be accessed via this.context.connection. Please refer to the networking docs for further information.

Accessing Needle Engine and components from anywhere

It is possible to access all the functionality described above using regular JavaScript code that is not inside components and lives somewhere else. All the components and functionality of the needle runtime is accessible via the global Needle namespace (you can write console.log(Needle) to get an overview)

You can find components using Needle.findObjectOfType(Needle.AudioSource) for example. It is recommended to cache those references, as searching the whole scene repeatedly is expensive. See the list for finding adding and removing components above.

For getting callbacks for the initial scene load see the following example:

<needle-engine loadstart="loadingStarted" progress="loadingProgress" loadfinished="loadingFinished"></needle-engine>

<script type="text/javascript">
function loadingStarted() { console.log("START") }
function loadingProgress() { console.log("LOADING...") }
function loadingFinished() { console.log("FINISHED!") }

You can also subscribe to the globale NeedleEngine (sometimes also referred to as ContextRegistry) to receive a callback when a Needle Engine context has been created or to access all available contexts:

import { NeedleEngine } from "@needle-tools/engine";
NeedleEngine.addContextCreatedCallback((args) => {
  const context = args.context;
  const scene = context.scene;
  const myInstance = GameObject.getComponentInChildren(scene, YourComponentType);

Another option is using the onInitialized(ctx => {}) lifecycle hook

You can also access all available contexts via NeedleEngine.Registered which returns the internal array. (Note that this array should not be modified but can be used to iterate all active contexts to modify settings, e.g. set all contexts to context.isPaused = true)

Below you find a list of available events on the static NeedleEngine type.
You can subscribe to those events via NeedleEngine.registerCallback(ContextEvent.ContextCreated, (args) => {})

ContextEvent options
ContextEvent.ContextRegisteredCalled when the context is registered to the registry.
ContextEvent.ContextCreationStartCalled before the first glb is loaded and can be used to initialize the physics engine. Can return a promise
ContextEvent.ContextCreatedCalled when the context has been created before the first frame
ContextEvent.ContextDestroyedCalled when the context has been destroyed
ContextEvent.MissingCameraCalled when the context could not find a camera, currently only called during creation
ContextEvent.ContextClearingCalled when the context is being cleared: all objects in the scene are being destroyed and internal state is reset
ContextEvent.ContextClearedCalled after the context has been cleared


The static Gizmos class can be used to draw lines, shapes and text which is mostly useful for debugging.
All gizmos function have multiple options for e.g. colors or for how long they should be displayed in the scene. Internally they are cached and re-used.

Gizmos.DrawLabelDraws a label with a background optionally. It can be attached to an object. Returns a Label handle which can be used to update the text.
Gizmos.DrawRayTakes an origin and direction in worldspace to draw an infinite ray line
Gizmos.DrawDirectionTakes a origin and direction to draw a direction in worldspace
Gizmos.DrawLineTakes two vec3 worldspace points to draw a line
Gizmos.DrawWireSphereDraws a wireframe sphere in worldspace
Gizmos.DrawSphereDraws a solid sphere in worldspace
Gizmos.DrawWireBoxDraws a wireframe box in worldspace
Gizmos.DrawWireBox3Draws a wireframe box3
Gizmos.DrawArrowDraws an arrow taking two points in worldspace

Serialization / Components in glTF files

To embed components and recreate components with their correct types in glTF, we also need to save non-primitive types (everything that is not a Number, Boolean or String). You can do so is adding a @serializable(<type>) decorator above your field or property.


import { Behaviour, serializable } from "@needle-tools/engine";
import { Object3D } from "three"

export class MyClass extends Behaviour {
    // this will be a "Transform" field in Unity
    myObjectReference: Object3D | null = null;
    // this will be a "Transform" array field in Unity
    // Note that the @serializable decorator contains the array content type! (Object3D and not Object3D[])
    myObjectReferenceList: Object3D[] | null = null;

To serialize from and to custom formats, it is possible to extend from the TypeSerializer class and create an instance. Use super() in the constructor to register supported types.

Note: In addition to matching fields, matching properties will also be exported when they match to fields in the typescript file.

Loading Scenes

Referenced Prefabs, SceneAssets and AssetReferencesopen in new window in Unity will automatically be exported as glTF files (please refer to the Export Prefabs documentation).

These exported gltf files will be serialized as plain string URIs. To simplify loading these from TypeScript components, we added the concept of AssetReference types. They can be loaded at runtime and thus allow to defer loading parts of your app or loading external content.


import { Behaviour, serializable, AssetReference } from "@needle-tools/engine";

export class MyClass extends Behaviour {

    // if you export a prefab or scene as a reference from Unity you'll get a path to that asset
    // which you can de-serialize to AssetReference for convenient loading
    myPrefab?: AssetReference;
    async start() {
      // directly instantiate
      const myInstance = await this.myPrefab?.instantiate();

      // you can also just load and instantiate later
      // const myInstance = await this.myPrefab.loadAssetAsync();
      // this.gameObject.add(myInstance)
      // this is useful if you know that you want to load this asset only once because it will not create a copy
      // since ``instantiate()`` does create a copy of the asset after loading it

AssetReferences are cached by URI, so if you reference the same exported glTF/Prefab in multiple components/scripts it will only be loaded once and then re-used.