Object Systems

Object systems are reusable pieces of code that can be attached to game objects during instantiation (Think React hooks, if you're familiar).

Objects instantiated this way are stored in the global store unless specifically ordered not to be.

You can read more about instantiating your own custom game elements in the customisation section, but for the most part in-built game objects (such as viewports, stages, sprites, plugins, etc.) will instantiate themselves in the game instance for you.

To attach an object system to an object that is not already equipped with one you can call the attachSystem method. Objects must be instantiated in a game instance first to have a game system attached to them.

[game].object.attachSystem(<obj>, <systems>)

Object <obj> Object to attach the event system(s) to.

Object <systems> Object indicating list of systems to attach to the given object.
The property value must be set to true to register.
The current valid object systems are:

Most in-built game objects will already come with object systems that are useful for their use case, so unless you are making your own custom game objects you may rarely need to attach extra object systems to objects you create.


Creating a custom sprite and then attaching the event and tween object system to it.

// Create a new game instance and an empty object.
const game = Whirl.Game();
const customSprite = {};
// Instantiate the empty object into the game instance.
game.object.init(customSprite, "Custom.Sprite");

// Attach the `event` and `tween` system.
game.object.attachSystem(customSprite, {
    event: true,
    tween: true

Object systems can also be attached with the init method during instantiation as a third argument.

game.object.init(customSprite, "Custom.Sprite", {
    event: true,
    tween: true

The Global Store

Most objects instantiated within a Whirl game instance are stored in what is called "The Global Store". This is a persistent list of all objects that exist in the current game instance.

You can see the raw global store of your game instance under [game].globalStore but you should never modify this directly. You should also never rely on the order of the array representing the raw global store as it can change between game updates, object modification and other various ways.

To traverse the global store you should use the provided methods under the object property of a game instance.



For all "Get ..." methods if no results are found (meaning no objects are matched) then an empty array will be returned ([]).

Get All

Returns an array of every item in the global store.


The returned array has no inherent ordering and thus the order the of the returned array will not necessarily be consistent on every call.

Get By ID

Returns an array of objects in the global store whose _id property match the given <id> search value.

All objects that are instantiated within a game instance (Regardless of whether they are stored within the global store or not) are assigned a unique _id integer value that uniquely identifies every object created under the game instance since the game was instantiated.

Keep in mind all IDs should be unique so although an array may be returned it should never have more than one value.


Integer <id> Unique ID number by which to search the global store by.

Get By Name

Returns an array of objects in the global store whose name property matches the given <name> search string.

Viewports, Stages, Sprites and Assets all a have name property that you provide when creating a new instance of them.


String <name> String to match an object's name by in the global store.

Get By Type

Returns an array of objects in the global store whose _type property matches the given <type> string.

All objects instantiated under a game instance give a name for their "type" that identifies where the object came from and its own class. For example, a viewport's _type is Whirl.Viewport, and a sprite's _type is Whirl.Sprite.

To learn more about types and making your own see the customisation section.


String <type> String to match an object's type by in the global store.

Destroy By ID

Removes an object from the global store given an <id> property and returns the removed object. Returns false if no object to remove is found.

Use with caution:
This method directly modifies the global store and therefore should not be used unless there are no other references to the object anywhere else in the game instance (such as being stored in a stage world, viewport, camera, etc.). Doing so may break functionality in unexpected and sometimes hard to debug ways.


Integer <id> Unique ID number by which to search the global store by and match an object to be removed.

Custom Events

Whirl uses a dynamic event system to emit information from objects that can be picked up by listeners on that object. Many Whirl objects come with their own premade events, but you can also make your own that listen on or emit events from any object that has the event system attached to it.

Events are identified by a given name. There can be multiple listeners on a single event that will all fire when that even is called. Listener callbacks are called in the order that the listeners were initially added in.

Events do not have to be initialised beforehand. You can listen on any event name and it will be fired if something emits to that same name.


Attach the event system to a game object:

[game].object.attachSystem([object], {event: true})



Adds a new event listener for the given event name.

[object].event.on(<name>, <callback>, <once>)

String <name> Name of the event to listen on.

Function <callback> Callback function that is called every time an event is emitted on the given event name.
Takes a single object parameter that contains the emitted data.
The object paramater also has attached to it the following properties:
_eventId - The ID of the current event listener.
_object - The object that the event is being called on.

Boolean <once> (Optional) (Default: false) If set to true will remove the event listener after one emit to the event name.


Listen for the event hit on the myPlayer object that when called upon will damage the player by the given damage value.

myPlayer.event.on("hit", (data) => {
    myPlayer.data.health -= data.damage;

Listen for the event loadedImage that is listened to once and then when emitted to stops listening.

myPlayer.event.on("loadedImage", (data) => {
    console.log("Player image loaded!");
}, true);

On Once

Implicitly the same as .event.on but with the <once> argument set to true.

See the 'On' method parameters as they are the same except with the last parameter omitted.


myPlayer.event.onOnce("loadedImage", (data) => {
    console.log("Player image loaded!");


Emits an event on the given name with given data.

[object].event.emit(<name>, <data>)

String <name> Name of the event to emit on.

Object <data> (Optional) (Default: {}) Data to emit with the event.
You can add any property to this object, but do not overwrite the additional properties added by the event system (_eventId and _object).


Emit the hit event on the myPlayer object that passes damage: 5 on the data object.

myPlayer.event.emit("hit", {
    damage: 5

Remove By ID

Removes a specific event listener by its unique identity number.

Each event listener has a unique identification number that is passed to the callback function whenever the listener is emitted to in the _eventId property.

[object].event.removeById(<name>, <id>)

String <name> Name of the event.

Integer <id> ID number of the listener within the event.


myPlayer.event.on("hit", (data) => {
    myPlayer.data.health -= data.damage;

    // Make the player invincible so they can't be hit anymore by removing the event listener
    myPlayer.event.removeById("name", data._eventId);

Remove All

Removes all event listeners on a specified event name.


String <name> Name of the event to remove all listeners from.


Remove all listeners listening on the hit event on the myPlayer object.


Animation Tweens

Tweens are instructions that continually put intermediate frames between two points over a given time.

Tweens are created, manipulated and deleted by the game instance's tween manager. You can create a tween using the tween manager directly or create a tween from object itself (on it's .tween property) which will implicitely call the tween manager.

Creating a tween using the tween manager does not require the object to have the tween system attached to it as tween data is stored separately within the tween manager itself. To use the tween shorthand [object].tween you must first ensure that the tween system is attached to the object.

Tweens are updated on the same tick as the main game loop, but the timing and duration is set independently of the game update rate. This means that the exact ending of a tween can occur at a different time to when the game finishes an update causing a slight millisecond delay between the tween finishing and the result being shown.



Attach the tween system to a game object:

[game].object.attachSystem([object], {tween: true})


Returns a Tween object that holds data about a tween and can be modified later.

Create a tween on an object.

Tweens cannot modify nested properties of an object. To modify a nested object then you must create a separate tween for that object itself.

// Create a tween using the Tween Manager
[game].tweenManager.create([object], [from], [to], [time], [presets])

// Create a tween using the Tween object system
[object].tween([from], [to], [time], [presets])

Object <object> Object that the tween will apply to.

Object <from> (Optional) (Default: {}) Object that defines properties of the given <object> to edit and their values that are set from the beginning of the tween.

Properties given here should correlate to the properties of the given <object>.

Object <to> Object that defines properties of the given <object> to tween their values to (as opposed to from) the ending of the tween.

Properties given here should correlate to the given properties of the given <object>.

If no properties are given to the <from> object then instead of transitioning the values between the <from> and <to> objects the values will be transitioned from their pre-existing state and increased by the values given in the <to> object.

For example, if an object's properties are {x: 20, y: 60} and the tween <from> object is {x: 50} and <to> is {x: 100} then the tween will transition the x property from 50 to 100.

If the <from> object is {} (or undefined) and <to> is {x: 100} then the tween will transition the x property from 20 to 120 as the x property was 20 and is now being increased by 100.

Integer <time> Time (in milliseconds) that the tween takes to transition between the <from> and <to> values.

Object <presets> Presets/Configuration to give to the tween. All presets are optional.

Function easing - Easing function to use for the tween. See all Whirl easing functions. You may also supply a custom easing function. (Default: Whirl.easing.linear).
Boolean start - Begin the tween animation immediately as it is created (Default: true).
Number step - Value to step between on each update loop. After each update by the tween the value will be rounded to the given <step> value (Default: No rounding).
Boolean roundValues - Whether the values being modified should be rounded to the nearest integer (Default: false).
Boolean loop - Whether the Tween will restart after completing. If a Tween has another Tween chained to it then it will not loop regardless of this flag (Default: false).
Boolean canPurge - Whether the Tween can be purged from the internal list of tweens stored in the tween manager (Default: true).

Child Hierarchy


Attach the child system to a game object:

[game].object.attachSystem([object], {child: true})