Remove Node.js dependency (events core usage) to ensure browser com…

…patibility

README.md

@@ -2,7 +2,7 @@
 
 ![npm version](https://img.shields.io/npm/v/@jpwilliams/waitgroup) ![Test on push](https://github.com/jpwilliams/waitgroup/workflows/Test%20on%20push/badge.svg) ![Downloads](https://img.shields.io/npm/dm/@jpwilliams/waitgroup)
 
-A tiny version of Golang's [WaitGroup](https://golang.org/pkg/sync/#WaitGroup) with typings, promises, and zero dependencies.
+A tiny version of Golang's [WaitGroup](https://golang.org/pkg/sync/#WaitGroup) for Node.js and the browser with typings, promises, and zero dependencies.
 
 ```sh
 npm install @jpwilliams/waitgroup

src/index.spec.ts

@@ -42,13 +42,13 @@ describe('WaitGroup', () => {
 		test('increments internal counter by default of 1', () => {
 			const wg = new WaitGroup()
 			wg.add()
-			expect(wg['_current']).toEqual(1)
+			expect(wg['current']).toEqual(1)
 		})
 
 		test('increments internal counter given value', () => {
 			const wg = new WaitGroup()
 			wg.add(3)
-			expect(wg['_current']).toEqual(3)
+			expect(wg['current']).toEqual(3)
 		})
 
 		test('throws if add() results in a negative counter', () => {
@@ -61,9 +61,9 @@ describe('WaitGroup', () => {
 		test('decrements internal counter by 1', () => {
 			const wg = new WaitGroup()
 			wg.add(3)
-			expect(wg['_current']).toEqual(3)
+			expect(wg['current']).toEqual(3)
 			wg.done()
-			expect(wg['_current']).toEqual(2)
+			expect(wg['current']).toEqual(2)
 		})
 
 		test('throws if done() results in a negative counter', () => {

src/index.ts

@@ -1,5 +1,3 @@
-import { EventEmitter } from 'events'
-
 /**
  * A WaitGroup waits for a collection of actions to finish.
  * The main goroutine calls `add` to set the number of actions to wait for.
@@ -10,35 +8,48 @@ import { EventEmitter } from 'events'
  * way Node functions, meaning `add`, `done` and `wait` can be called at any time, in any order.
  */
 export class WaitGroup {
-	private _current = 0
-	private _emitter = new EventEmitter()
+	private current = 0
+	private queued: (() => void)[] = []
+
+	private queue (fn: () => void) {
+		if (this.current === 0) {
+			fn()
+		} else {
+			this.queued.push(fn)
+		}
+	}
+
+	private resolveQueue () {
+		while (this.queued.length > 0) {
+			this.queued.shift()?.()
+		}
+	}
 
 	/**
-	 * Adds a delta, which may be negative, to the WaitGroup counter.
-	 * If the counter becomes zero, all promises returned from `wait` are resolved.
-	 * If the counter goes negative, an error is thrown.
-	 */
+   * Adds a delta, which may be negative, to the WaitGroup counter.
+   * If the counter becomes zero, all promises returned from `wait` are resolved.
+   * If the counter goes negative, an error is thrown.
+   */
 	public add (delta: number = 1): void {
-		this._current += delta
-		if (this._current < 0) throw new Error('Negative WaitGroup counter')
-		if (this._current === 0) this._emitter.emit('done')
+		this.current += delta
+		if (this.current < 0) throw new Error('Negative WaitGroup counter')
+		if (this.current === 0) this.resolveQueue()
 	}
 
 	/**
-	 * Decrements the WaitGroup counter by one.
-	 */
+   * Decrements the WaitGroup counter by one.
+   */
 	public done (): void {
 		this.add(-1)
 	}
 
 	/**
-	 * Returns a promise that resolves when the WaitGroup counter is zero.
-	 * If the counter is zero when the method is called, it's resolved immediately.
-	 */
+   * Returns a promise that resolves when the WaitGroup counter is zero.
+   * If the counter is zero when the method is called, it's resolved immediately.
+   */
 	public wait (): Promise<void> {
 		return new Promise((resolve) => {
-			if (this._current === 0) return resolve()
-			this._emitter.once('done', () => resolve())
+			this.queue(() => resolve())
 		})
 	}
 }