Merge pull request #89 from Sykander/async-reduce

Async reduce

Author: Sykander

package.json

@@ -5,15 +5,15 @@
   "main": "src/index.js",
   "types": "types/index.d.ts",
   "scripts": {
-    "test:type-definitions": "./node_modules/.bin/tsc test/typings.ts && node test/typings.js",
+    "test:type-definitions": "tsc test/typings.ts && node test/typings.js",
     "test:code-style": "npm run lint:check",
-    "test:unit-tests": "./node_modules/.bin/mocha test/**/*.spec.js",
-    "test:coverage-report": "./node_modules/.bin/nyc npm run test:unit-tests --silent",
-    "test:coverage-check": "./node_modules/.bin/nyc check-coverage",
+    "test:unit-tests": "mocha test/**/*.spec.js",
+    "test:coverage-report": "nyc npm run test:unit-tests --silent",
+    "test:coverage-check": "nyc check-coverage",
     "test:coverage": "npm run test:coverage-report; npm run test:coverage-check",
     "test": "npm run test:unit-tests && npm run test:code-style && npm run test:type-definitions && npm run test:coverage",
-    "lint:fix": "./node_modules/.bin/prettier --write 'src/**/*.{js,ts,css,html}' --write 'test/**/*.{js,ts,css,html}'",
-    "lint:check": "./node_modules/.bin/eslint src test",
+    "lint:fix": "prettier --write 'src/**/*.{js,ts,css,html}' --write 'test/**/*.{js,ts,css,html}'",
+    "lint:check": "eslint src test",
     "lint": "npm run lint:fix --silent && npm run lint:check",
     "prepublishOnly": "npm ci && npm test",
     "postlint": "echo \"No issues.\"",

src/async-array.js

@@ -6,7 +6,8 @@ const { asyncFind } = require('./async-find'),
 	{ asyncMapSort } = require('./async-map-sort'),
 	{ asyncReduce } = require('./async-reduce'),
 	{ asyncSort } = require('./async-sort'),
-	{ compareByUnicode } = require('./helpers');
+	{ compareByUnicode } = require('./helpers'),
+	{ noParam } = require('./constants');
 
 /**
  * Async Array
@@ -68,11 +69,11 @@ class AsyncArray extends Array {
 		return asyncMapSort(iterable, mappingCallback, comparisonCallback);
 	}
 
-	asyncReduce(callback, accumulator = undefined) {
+	asyncReduce(callback, accumulator = noParam) {
 		return asyncReduce(this, callback, accumulator);
 	}
 
-	static asyncReduce(iterable, callback, accumulator = undefined) {
+	static asyncReduce(iterable, callback, accumulator = noParam) {
 		return asyncReduce(iterable, callback, accumulator);
 	}
 

src/async-filter.js

@@ -20,8 +20,7 @@ async function asyncFilter(iterable, callback, thisArg = undefined) {
 		iterable,
 		await Promise.all(
 			mapIterable(iterable, callback.bind(thisArg), {
-				useEmptyElements: false,
-				newlyAddedElements: false
+				useEmptyElements: false
 			})
 		)
 	);

src/async-find-index.js

@@ -17,8 +17,7 @@ async function asyncFindIndex(iterable, callback, thisArg = undefined) {
 	validateIsFunction(callback);
 
 	const tasks = mapIterable(iterable, callback.bind(thisArg), {
-		useEmptyElements: true,
-		newlyAddedElements: false
+		useEmptyElements: true
 	});
 
 	return Promise.race([

src/async-find.js

@@ -17,8 +17,7 @@ async function asyncFind(iterable, callback, thisArg = undefined) {
 	validateIsFunction(callback);
 
 	const tasks = mapIterable(iterable, callback.bind(thisArg), {
-		useEmptyElements: true,
-		newlyAddedElements: false
+		useEmptyElements: true
 	});
 
 	return iterable[

src/async-for-each.js

@@ -17,8 +17,7 @@ async function asyncForEach(iterable, callback, thisArg = undefined) {
 
 	await Promise.all(
 		mapIterable(iterable, callback.bind(thisArg), {
-			useEmptyElements: false,
-			newlyAddedElements: false
+			useEmptyElements: false
 		})
 	);
 }

src/async-map.js

@@ -18,8 +18,7 @@ async function asyncMap(iterable, callback, thisArg = undefined) {
 
 	return Promise.all(
 		mapIterable(iterable, callback.bind(thisArg), {
-			useEmptyElements: false,
-			newlyAddedElements: false
+			useEmptyElements: false
 		})
 	);
 }

src/async-reduce.js

@@ -1,3 +1,10 @@
+const {
+		validateIsIterable,
+		validateIsFunction,
+		validateNonZeroLength
+	} = require('./validation'),
+	{ noParam } = require('./constants');
+
 /**
  * Async Reduce
  * ============
@@ -6,10 +13,35 @@
  * @async
  * @param {Object} iterable
  * @param {Function} callback - callback(currentValue, index, array)
- * @param {any} [accumulator]
+ * @param {any} [accumulator=noParam]
  * @return {any}
  * @throws {TypeError}
  */
-async function asyncReduce() {}
+async function asyncReduce(iterable, transducer, accumulator = noParam) {
+	validateIsIterable(iterable);
+	validateIsFunction(transducer);
+	const length = iterable.length;
+	let i = 0;
+
+	if (accumulator === noParam) {
+		try {
+			validateNonZeroLength(iterable);
+		} catch (e) {
+			throw new TypeError(
+				'asyncReduce of empty array with no accumulator given'
+			);
+		}
+
+		accumulator = iterable[0];
+		i = 1;
+	}
+
+	for (; i < length; i++) {
+		// eslint-disable-next-line no-await-in-loop
+		accumulator = await transducer(accumulator, iterable[i], i, iterable);
+	}
+
+	return accumulator;
+}
 
 module.exports = { asyncReduce };

src/constants.js

@@ -0,0 +1,7 @@
+/**
+ * @const {Symbol} noParam
+ * For representing when no parameter was passed to a function
+ */
+const noParam = Symbol('No argument passed for this parameter');
+
+module.exports = { noParam };

src/helpers.js

@@ -7,26 +7,18 @@
  * @param {Function} callback
  * @param {Object} [options]
  * @param {Boolean} [options.useEmptyElements=true] - use empty elements of the array ?
- * @param {Boolean} [options.newlyAddedElements=false] - visit newly added elements ?
  * @return {Array}
  */
-function mapIterable(
-	iterable,
-	callback,
-	{ useEmptyElements = true, newlyAddedElements = false } = {}
-) {
-	const tasks = [];
+function mapIterable(iterable, callback, { useEmptyElements = true } = {}) {
+	const tasks = [],
+		length = iterable.length;
 
-	for (let index = 0, length = iterable.length; index < length; index++) {
+	for (let index = 0; index < length; index++) {
 		if (!useEmptyElements && !(index in iterable)) {
 			continue;
 		}
 
 		tasks.push(callback(iterable[index], index, iterable));
-
-		if (newlyAddedElements) {
-			length = iterable.length;
-		}
 	}
 
 	return tasks;