fix(clearQueue): reject pending promises

BREAKING CHANGE: when clearQueue() is called, promises for queued function calls will be rejected.

fix sindresorhus#25

index.js

@@ -13,7 +13,7 @@ const pLimit = concurrency => {
 		activeCount--;
 
 		if (queue.length > 0) {
-			queue.shift()();
+			queue.shift().run();
 		}
 	};
 
@@ -27,15 +27,17 @@ const pLimit = concurrency => {
 		result.then(next, next);
 	};
 
-	const enqueue = (fn, resolve, ...args) => {
+	const enqueue = (fn, resolve, reject, ...args) => {
 		if (activeCount < concurrency) {
 			run(fn, resolve, ...args);
 		} else {
-			queue.push(run.bind(null, fn, resolve, ...args));
+			queue.push({run: run.bind(null, fn, resolve, ...args), reject});
 		}
 	};
 
-	const generator = (fn, ...args) => new Promise(resolve => enqueue(fn, resolve, ...args));
+	const generator = (fn, ...args) => new Promise(
+		(resolve, reject) => enqueue(fn, resolve, reject, ...args)
+	);
 	Object.defineProperties(generator, {
 		activeCount: {
 			get: () => activeCount
@@ -45,6 +47,7 @@ const pLimit = concurrency => {
 		},
 		clearQueue: {
 			value: () => {
+				queue.forEach(({reject}) => reject(new Error('queue cleared before function was invoked')));
 				queue.length = 0;
 			}
 		}

test.js

@@ -125,7 +125,9 @@ test('clearQueue', t => {
 	const limit = pLimit(1);
 
 	Array.from({length: 1}, () => limit(() => delay(1000)));
-	Array.from({length: 3}, () => limit(() => delay(1000)));
+	Array.from({length: 3}, () => limit(() => delay(1000)).catch(
+		error => t.is(error.message, 'queue cleared before function was invoked')
+	));
 
 	t.is(limit.pendingCount, 3);
 	limit.clearQueue();