Add support for clearing the queue (#20)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

index.d.ts

@@ -18,6 +18,15 @@ export interface Limit {
 	The number of promises that are waiting to run (i.e. their internal `fn` was not called yet).
 	*/
 	readonly pendingCount: number;
+
+	/**
+	Discard pending promises that are waiting to run.
+
+	This might be useful if you want to teardown the queue at the end of your program's lifecycle or discard any function calls referencing an intermediary state of your app.
+
+	Note: This does not cancel promises that are already running.
+	*/
+	clearQueue(): void;
 }
 
 /**

index.js

@@ -42,6 +42,11 @@ const pLimit = concurrency => {
 		},
 		pendingCount: {
 			get: () => queue.length
+		},
+		clearQueue: {
+			value: () => {
+				queue.length = 0;
+			}
 		}
 	});
 

index.test-d.ts

@@ -16,3 +16,5 @@ expectType<Promise<string>>(limit((a: string, b: number) => Promise.resolve(''),
 
 expectType<number>(limit.activeCount);
 expectType<number>(limit.pendingCount);
+
+expectType<void>(limit.clearQueue());

readme.md

@@ -66,6 +66,14 @@ The number of promises that are currently running.
 
 The number of promises that are waiting to run (i.e. their internal `fn` was not called yet).
 
+### limit.clearQueue()
+
+Discard pending promises that are waiting to run.
+
+This might be useful if you want to teardown the queue at the end of your program's lifecycle or discard any function calls referencing an intermediary state of your app.
+
+Note: This does not cancel promises that are already running.
+
 ## FAQ
 
 ### How is this different from the [`p-queue`](https://github.com/sindresorhus/p-queue) package?

test.js

@@ -121,6 +121,17 @@ test('activeCount and pendingCount properties', async t => {
 	t.is(limit.pendingCount, 0);
 });
 
+test('clearQueue', t => {
+	const limit = pLimit(1);
+
+	Array.from({length: 1}, () => limit(() => delay(1000)));
+	Array.from({length: 3}, () => limit(() => delay(1000)));
+
+	t.is(limit.pendingCount, 3);
+	limit.clearQueue();
+	t.is(limit.pendingCount, 0);
+});
+
 test('throws on invalid concurrency argument', async t => {
 	await t.throwsAsync(pLimit(0));
 	await t.throwsAsync(pLimit(-1));