# Life cycle callbacks

Cocos Creator 3D provides life cycle callback functions for component scripts. As long as the user defines a specific callback function, Cocos Creator 3D will automatically execute related scripts in a specific period, and the user does not need to call them manually.

The life cycle callback functions currently provided to users mainly include:

onLoad()
start()
update()
lateUpdate()
onDestroy()
onEnable()
onDisable()

onLoad()

In the initialization phase of the component script, the onLoad() callback function is available. The onLoad() callback will be triggered when the node is activated for the first time, such as when the scene is loaded or the node is activated. In the onLoad() stage, it is guaranteed that you can get other nodes in the scene and the resource data associated with the nodes. onLoad() will always be executed before any start method is called, which can be used to arrange the initialization sequence of the script. Usually, some initialization related operations are performed in the onLoad() stage. Example:

import { _decorator, Component, Node, SpriteFrame, find } from "cc";
const { ccclass, property } = _decorator;

@ccclass("test")
export class test extends Component {
    @property({type:SpriteFrame})
    bulletSprite=null;
    @property({type:Node})
    gun=null;

    _bulletRect=null;

    onLoad(){
        this._bulletRect=this.bulletSprite.getRect();
        this.gun = find('hand/weapon'),this.node;
    }
}

start()

The start() callback function will be triggered before the first activation of the component, that is, before the first execution of update(). start() is usually used to initialize some intermediate state data. These data may change during update and are frequently enabled and disabled. Example:

import { _decorator, Component, Node } from "cc";
const { ccclass, property } = _decorator;

@ccclass("starttest")
export class starttest extends Component {

    private _timer: number = 0.0;

    start () {
        this._timer = 1.0;
    }

    update (deltaTime: number) {
        this._timer += deltaTime;
        if(this._timer >= 10.0){
            console.log('I am done!');
            this.enabled = false;
        }
     }
}

update()

A key point of game development is to update the behavior, state and orientation of objects before each frame of rendering. These update operations are usually placed in the update() callback. Example:

import { _decorator, Component, Node } from "cc";
const { ccclass, property } = _decorator;

@ccclass("updatetest")
export class updatetest extends Component {

    update (deltaTime: number) {
        this.node.setPosition(0.0,40.0*deltaTime,0.0);
    }
}

lateUpdate()

update() will be executed before all animations are updated, but if developer's need to perform some additional operations after the animations (such as animation, particles, physics, etc.) are updated, or it is needed to execute the update() of all components after doing other operations, use the lateUpdate() callback. Example:

import { _decorator, Component, Node } from "cc";
const { ccclass, property } = _decorator;

@ccclass("lateupdatetest")
export class lateupdatetest extends Component {

    lateUpdate (deltaTime: number) {
        this.node.setPosition(0.0,50,0.0);
    }
}

onEnable()

When the enabled attribute of the component changes from false to true, or the node's active attribute changes from false to true, the onEnable() callback will be activated. If the node is created for the first time and enabled is true, it will be called after onLoad() but before start().

onDisable()

When the enabled attribute of the component changes from true to false, or the node's active attribute changes from true to false, the onDisable() callback will be activated.

onDestroy()

When the component or the node where it calls destroy(), the onDestroy() callback will be called, and the component will be recycled when the frame ends.

Continue to Create and Destroy Nodes documentation.

Life Cycle Callbacks