mixins.md

Mixins

Introduction

A mixin is used to inject code in the EventDispatcher/EventQueue to extend the functionalities. In this document we will use EventDispatcher as the example, the usage for EventQueue is exactly the same.
All methods and properties in the mixin are copied to the EventDispatcher/EventQueue and can be used as if they are part of the EventDispatcher/EventQueue.

Define a mixin

A mixin is a class, or to say, a function object.
A typical mixin should look like,

class MyMixin {
  public propA: number = 1;
  public propB: number = 5;
}

Inject(enable) mixins to EventDispatcher

To enable mixins, add them to the mixins property in the parameters object. For example, to enable MixinFilter, create the dispatcher as,

const dispatcher = new EventDispatcher({
  mixins: [new MixinFilter()],
});

If there are multiple mixins, add them to mixins array.

Optional interceptor points

A mixin can have special named functions that are called at certain point.
Currently there is only one special function,

public mixinBeforeDispatch(...args: any[]): boolean;

mixinBeforeDispatch is called before any event is dispatched in both EventDispatcher and EventQueue. It receives an array that contains the arguments passed to EventDispatcher.dispatch. So the function can modify the arguments in the array, then the listeners will see the modified values.
The function returns true to continue the dispatch, false will stop any further dispatching.
For multiple mixins, this function is called in the order of they appearing in mixins in the parameters object.