Typed Event Emitter

You can use node module event-emitter with strict type in typescript.

Installation

npm i @kim-kijun/typed-event-emitter

Usage

Class TypedEventEmitter

You can use TypedEventEmitter like EventEmitter. (It's same.)

1import { TypedEventEmitter } from '@kim-kijun/typed-event-emitter';
2
3// Predefine event types
4type MyEvents = {
5  loadedEnd(): void;
6  changeValue(value: string): void;
7  pressKey(key: string, keycode: number, ctrlKey?: boolean): void;
8};
9
10// Call constructor with the defined type.
11const eventEmitter = new TypedEventEmitter<MyEvents>();

You can check valid name of the event.

1eventEmitter.on('loadidEnd', () => {}); // Type Error! - wrong event name
2eventEmitter.on('loadedEnd', () => {}); // Good!

You can check type of the arguments of callback function.

1eventEmitter.on('changeValue', (value) => {
2  let fixed = value.toFixed(2); // Type Error! - 'value' should be used as string type
3});
4eventEmitter.on('changeValue', (value) => {
5  let threeStr = value.slice(0, 3); // Good!
6});

You can check type of arguments when emit the event.

1eventEmitter.emit('pressKey', 'a', '80', true); // Type Error! - second argument should be number.
2eventEmitter.emit('pressKey', 'a', 0, true); // Good!

You can inherit class like original 'EventEmitter'

1class MyEventEmitter extends TypedEventEmitter<MyEvents> {...}
2const myEventEmitter = new MyEventEmitter();
3myEventEmitter.on('loadidEnd', () => {}); // Type Error!
4myEventEmitter.on('loadedEnd', () => {}); // Good!

You can get help with autocomplete in your IDE.

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Utility Types

Base

1type MyEvents = {
2  loadedEnd(): void;
3  changeValue(value: string): void;
4  pressKey(key: string, keycode: number, ctrlKey?: boolean): void;
5};
6const eventEmitter = new TypedEventEmitter<MyEvents>();

type EventName

1import { EventName } from '@kim-kijun/typed-event-emitter';
2type ExtractedEvents = EventName<MyEvents>;
3// 'loadedEnd' | 'changeValue' | 'pressKey'

type EventHandler

1import { EventHandler } from '@kim-kijun/typed-event-emitter';
2type HandlerChangeValue = EventHandler<MyEvents, 'changeValue'>;
3// (value: string): void

type EventHandlerParams

1import { EventHandlerParams } from '@kim-kijun/typed-event-emitter';
2type HandlerParamsPressKey = EventHandlerParams<MyEvents, 'pressKey'>;
3// [string, number, boolean | undefined]

type ExtractEventType

1import { ExtractEventType } from '@kim-kijun/typed-event-emitter';
2type ExtractedEvents = ExtractEventType<typeof eventEmitter>;
3// equals to 'MyEvents'