The following table contains available Typescript decorators that Needle Engine provides.

You can think of them as Attributes on steroids (if you are familiar with C#) - they can be added to classes, fields or methods in Typescript to provide additional functionality.

Field & Property Decorators
@serializable()Add to exposed / serialized fields. Is used when loading glTF files that have been exported with components from Unity or Blender.
@syncField()Add to a field to network the value when it changes. You can pass in a method to be called when the field changes
@validate()Add to receive callbacks in the component event method onValidate whenever the value changes. This behaves similar to Unity's onValidate.
Method Decorators
@prefix(<type>) (experimental)Can be used to easily inject custom code into other components. Optionally return false to prevent the original method from being executed. See the example below
Class Decorators
@registerTypeNo argument. Can be added to a custom component class to be registered to the Needle Engine types and to enable hot reloading support.



export class ButtonObject extends Behaviour {
    // you can omit the type if it's a primitive 
    // e.g. Number, String or Bool
    myNumber: number = 42;

    // otherwise add the concrete type that you want to serialize to
    onClick?: EventList;

    myComponent: SomeComponentType;

    // Note that for arrays you still add the concrete type (not the array)
    myObjects: Object3D[];


export class MyScript extends Behaviour {

    myNumber: number = 42;

    private onNumberChanged(newValue : number, oldValue : number){
        console.log("Number changed from ", oldValue, "to", newValue)


export class MyScript extends Behaviour {

    myNumber?: number;

    start() { setInterval(() => this.myNumber = Math.random(), 1000) }

    onValidate(fieldName: string) {
        console.log("Validate", fieldName, this.myNumber);


Live exampleopen in new window

import { Camera } from "@needle-tools/engine";
class YourClass {
    @prefix(Camera) // < this is type that has the method you want to change
    awake() { // < this is the method name you want to change

        // this is now called before the Camera.awake method runs
        // NOTE: `this` does now refer to the Camera instance and NOT `YourClass` anymore. This allows you to access internal state of the component as well
        console.log("Hello camera:", this)
        // optionally return false if you want to prevent the default behaviour