Class Script

The Script class is the fundamental base class for all scripts within PlayCanvas. It provides the minimal interface required for a script to be compatible with both the Engine and the Editor.

At its core, a script is simply a collection of methods that are called at various points in the Engine's lifecycle. These methods are:

Script#initialize - Called once when the script is initialized Script#postInitialize - Called once after all scripts have been initialized Script#update - Called every frame, if the script is enabled Script#postUpdate - Called every frame, after all scripts have been updated Script#swap - Called when a script is redefined

These methods are entirely optional, but provide a useful way to manage the lifecycle of a script and perform any necessary setup and cleanup.

Below is a simple example of a script that rotates an entity every frame.

Example

class EntityRotator extends Script {
    update() {
        this.entity.rotateLocal(0, 1, 0);
    }
}

When this script is attached to an entity, the update will be called every frame, slowly rotating the entity around the Y-axis.

For more information on how to create scripts, see the Scripting Overview.

Hierarchy (View Summary)

Constructors

constructor

Properties

app entity

Accessors

enabled scriptName

Methods

fire hasEvent initScript off on once

Events

EVENT_ATTR EVENT_DESTROY EVENT_DISABLE EVENT_ENABLE EVENT_ERROR EVENT_STATE

Constructors

constructor

Properties

app

app: AppBase

The AppBase that the instance of this type belongs to.

entity

entity: Entity

The Entity that the instance of this type belongs to.

Accessors

enabled

  • set enabled(value: boolean): void

  • True if the instance of this type is in running state. False when script is not running, because the Entity or any of its parents are disabled or the ScriptComponent is disabled or the Script Instance is disabled. When disabled no update methods will be called on each tick. initialize and postInitialize methods will run once when the script instance is in enabled state during app tick.

    Parameters

    • value: boolean

    Returns void

StaticscriptName

Methods

fire

  • fire(
        name: string,
        arg1?: any,
        arg2?: any,
        arg3?: any,
        arg4?: any,
        arg5?: any,
        arg6?: any,
        arg7?: any,
        arg8?: any,
    ): EventHandler

  • Fire an event, all additional arguments are passed on to the event listener.

    Parameters

    • name: string

      Name of event to fire.

    • Optionalarg1: any

      First argument that is passed to the event handler.

    • Optionalarg2: any

      Second argument that is passed to the event handler.

    • Optionalarg3: any

      Third argument that is passed to the event handler.

    • Optionalarg4: any

      Fourth argument that is passed to the event handler.

    • Optionalarg5: any

      Fifth argument that is passed to the event handler.

    • Optionalarg6: any

      Sixth argument that is passed to the event handler.

    • Optionalarg7: any

      Seventh argument that is passed to the event handler.

    • Optionalarg8: any

      Eighth argument that is passed to the event handler.

    Returns EventHandler

    Self for chaining.

    Example

    obj.fire('test', 'This is the message');

hasEvent

  • hasEvent(name: string): boolean

  • Test if there are any handlers bound to an event name.

    Parameters

    • name: string

      The name of the event to test.

    Returns boolean

    True if the object has handlers bound to the specified event name.

    Example

    obj.on('test', function () { }); // bind an event to 'test'
    obj.hasEvent('test'); // returns true
    obj.hasEvent('hello'); // returns false

ProtectedinitScript

off

  • off(name?: string, callback?: HandleEventCallback, scope?: object): EventHandler

  • Detach an event handler from an event. If callback is not provided then all callbacks are unbound from the event, if scope is not provided then all events with the callback will be unbound.

    Parameters

    • Optionalname: string

      Name of the event to unbind.

    • Optionalcallback: HandleEventCallback

      Function to be unbound.

    • Optionalscope: object

      Scope that was used as the this when the event is fired.

    Returns EventHandler

    Self for chaining.

    Example

    const handler = function () {
    };
    obj.on('test', handler);

    obj.off(); // Removes all events
    obj.off('test'); // Removes all events called 'test'
    obj.off('test', handler); // Removes all handler functions, called 'test'
    obj.off('test', handler, this); // Removes all handler functions, called 'test' with scope this

on

  • on(name: string, callback: HandleEventCallback, scope?: object): EventHandle

  • Attach an event handler to an event.

    Parameters

    • name: string

      Name of the event to bind the callback to.

    • callback: HandleEventCallback

      Function that is called when event is fired. Note the callback is limited to 8 arguments.

    • Optionalscope: object = ...

      Object to use as 'this' when the event is fired, defaults to current this.

    Returns EventHandle

    Can be used for removing event in the future.

    Example

    obj.on('test', function (a, b) {
        console.log(a + b);
    });
    obj.fire('test', 1, 2); // prints 3 to the console

    Example

    const evt = obj.on('test', function (a, b) {
        console.log(a + b);
    });
    // some time later
    evt.off();

once

  • once(name: string, callback: HandleEventCallback, scope?: object): EventHandle

  • Attach an event handler to an event. This handler will be removed after being fired once.

    Parameters

    • name: string

      Name of the event to bind the callback to.

    • callback: HandleEventCallback

      Function that is called when event is fired. Note the callback is limited to 8 arguments.

    • Optionalscope: object = ...

      Object to use as 'this' when the event is fired, defaults to current this.

    Returns EventHandle

    • can be used for removing event in the future.

    Example

    obj.once('test', function (a, b) {
        console.log(a + b);
    });
    obj.fire('test', 1, 2); // prints 3 to the console
    obj.fire('test', 1, 2); // not going to get handled

Events

StaticEVENT_ATTR

EVENT_ATTR: string = 'attr'

Fired when script attributes have changed. This event is available in two forms. They are as follows:

  1. attr - Fired for any attribute change. The handler is passed the name of the attribute that changed, the value of the attribute before the change and the value of the attribute after the change.
  2. attr:[name] - Fired for a specific attribute change. The handler is passed the value of the attribute before the change and the value of the attribute after the change.

Example

export class PlayerController extends Script {
    initialize() {
        this.on('attr', (name, newValue, oldValue) => {
            console.log(`Attribute '${name}' changed from '${oldValue}' to '${newValue}'`);
        });
    }
};

Example

export class PlayerController extends Script {
    initialize() {
        this.on('attr:speed', (newValue, oldValue) => {
            console.log(`Attribute 'speed' changed from '${oldValue}' to '${newValue}'`);
        });
    }
};

StaticEVENT_DESTROY

EVENT_DESTROY: string = 'destroy'

Fired when a script instance is destroyed and removed from component.

Example

export class PlayerController extends Script {
    initialize() {
        this.on('destroy', () => {
            // no longer part of the entity
            // this is a good place to clean up allocated resources used by the script
        });
    }
};

StaticEVENT_DISABLE

EVENT_DISABLE: string = 'disable'

Fired when a script instance becomes disabled.

Example

export class PlayerController extends Script {
    initialize() {
        this.on('disable', () => {
            // Script Instance is now disabled
        });
    }
};

StaticEVENT_ENABLE

EVENT_ENABLE: string = 'enable'

Fired when a script instance becomes enabled.

Example

export class PlayerController extends Script {
    initialize() {
        this.on('enable', () => {
            // Script Instance is now enabled
        });
    }
};

StaticEVENT_ERROR

EVENT_ERROR: string = 'error'

Fired when a script instance had an exception. The script instance will be automatically disabled. The handler is passed an Error object containing the details of the exception and the name of the method that threw the exception.

Example

export class PlayerController extends Script {
    initialize() {
        this.on('error', (err, method) => {
            // caught an exception
            console.log(err.stack);
        });
    }
};

StaticEVENT_STATE

EVENT_STATE: string = 'state'

Fired when a script instance changes state to enabled or disabled. The handler is passed a boolean parameter that states whether the script instance is now enabled or disabled.

Example

export class PlayerController extends Script {
    initialize() {
        this.on('state', (enabled) => {
            console.log(`Script Instance is now ${enabled ? 'enabled' : 'disabled'}`);
        });
    }
};

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