Add support for multiple pMapSkip's (#52)

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

index.js

@@ -23,7 +23,7 @@ export default async function pMap(
 
 		const result = [];
 		const errors = [];
-		const skippedIndexes = [];
+		const skippedIndexesMap = new Map();
 		let isRejected = false;
 		let isResolved = false;
 		let isIterableDone = false;
@@ -59,15 +59,28 @@ export default async function pMap(
 				if (resolvingCount === 0 && !isResolved) {
 					if (!stopOnError && errors.length > 0) {
 						reject(new AggregateError(errors));
-					} else {
-						isResolved = true;
+						return;
+					}
 
-						for (const skippedIndex of skippedIndexes) {
-							result.splice(skippedIndex, 1);
-						}
+					isResolved = true;
 
+					if (!skippedIndexesMap.size) {
 						resolve(result);
+						return;
 					}
+
+					const pureResult = [];
+
+					// Support multiple `pMapSkip`'s.
+					for (const [index, value] of result.entries()) {
+						if (skippedIndexesMap.get(index) === pMapSkip) {
+							continue;
+						}
+
+						pureResult.push(value);
+					}
+
+					resolve(pureResult);
 				}
 
 				return;
@@ -86,12 +99,13 @@ export default async function pMap(
 
 					const value = await mapper(element, index);
 
+					// Use Map to stage the index of the element.
 					if (value === pMapSkip) {
-						skippedIndexes.push(index);
-					} else {
-						result[index] = value;
+						skippedIndexesMap.set(index, value);
 					}
 
+					result[index] = value;
+
 					resolvingCount--;
 					await next();
 				} catch (error) {

test-multiple-pmapskips-performance.js

@@ -0,0 +1,37 @@
+import test from 'ava';
+import inRange from 'in-range';
+import timeSpan from 'time-span';
+import pMap, {pMapSkip} from './index.js';
+
+function generateSkipPerformanceData(length) {
+	const data = [];
+	for (let index = 0; index < length; index++) {
+		data.push(pMapSkip);
+	}
+
+	return data;
+}
+
+test('multiple pMapSkips - algorithmic complexity', async t => {
+	const testData = [generateSkipPerformanceData(1000), generateSkipPerformanceData(10000), generateSkipPerformanceData(100000)];
+	const testDurationsMS = [];
+
+	for (const data of testData) {
+		const end = timeSpan();
+		// eslint-disable-next-line no-await-in-loop
+		await pMap(data, async value => value);
+		testDurationsMS.push(end());
+	}
+
+	for (let index = 0; index < testDurationsMS.length - 1; index++) {
+		// Time for 10x more items should take between 9x and 11x more time.
+		const smallerDuration = testDurationsMS[index];
+		const longerDuration = testDurationsMS[index + 1];
+
+		// The longer test needs to be a little longer and also not 10x more than the
+		// shorter test. This is not perfect... there is some fluctuation.
+		// The idea here is to catch a regression that makes `pMapSkip` handling O(n^2)
+		// on the number of `pMapSkip` items in the input.
+		t.true(inRange(longerDuration, {start: 1.2 * smallerDuration, end: 15 * smallerDuration}));
+	}
+});

test.js

@@ -155,6 +155,28 @@ test('pMapSkip', async t => {
 	], async value => value), [1, 2]);
 });
 
+test('multiple pMapSkips', async t => {
+	t.deepEqual(await pMap([
+		1,
+		pMapSkip,
+		2,
+		pMapSkip,
+		3,
+		pMapSkip,
+		pMapSkip,
+		4
+	], async value => value), [1, 2, 3, 4]);
+});
+
+test('all pMapSkips', async t => {
+	t.deepEqual(await pMap([
+		pMapSkip,
+		pMapSkip,
+		pMapSkip,
+		pMapSkip
+	], async value => value), []);
+});
+
 test('all mappers should run when concurrency is infinite, even after stop-on-error happened', async t => {
 	const input = [1, async () => delay(300, {value: 2}), 3];
 	const mappedValues = [];
@@ -269,6 +291,28 @@ test('asyncIterator - pMapSkip', async t => {
 	]), async value => value), [1, 2]);
 });
 
+test('asyncIterator - multiple pMapSkips', async t => {
+	t.deepEqual(await pMap(new AsyncTestData([
+		1,
+		pMapSkip,
+		2,
+		pMapSkip,
+		3,
+		pMapSkip,
+		pMapSkip,
+		4
+	]), async value => value), [1, 2, 3, 4]);
+});
+
+test('asyncIterator - all pMapSkips', async t => {
+	t.deepEqual(await pMap(new AsyncTestData([
+		pMapSkip,
+		pMapSkip,
+		pMapSkip,
+		pMapSkip
+	]), async value => value), []);
+});
+
 test('asyncIterator - all mappers should run when concurrency is infinite, even after stop-on-error happened', async t => {
 	const input = [1, async () => delay(300, {value: 2}), 3];
 	const mappedValues = [];