Engine API Reference - v2.6.1
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    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.

    class EntityRotator extends Script {
        update(dt) {
            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)

    Index

    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

    Properties

    app: AppBase

    The AppBase that the instance of this script belongs to.

    entity: Entity

    The Entity that the instance of this script belongs to.

    Accessors

    • set enabled(value: any): void

      True if the instance of this script 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 the enabled state during an app tick.

      Parameters

      • value: any

      Returns void

    Methods

    • 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.

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

    • 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.

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

    • 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: any

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

      Returns EventHandler

      Self for chaining.

      const handler = () => {};
      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

    • 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: any = ...

        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.

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

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

    • 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: any = ...

        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.
      obj.once('test', (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

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

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

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

    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
            });
        }
    };
    EVENT_DISABLE: string = 'disable'

    Fired when a script instance becomes disabled.

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

    Fired when a script instance becomes enabled.

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

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

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

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