reduce 函数概述
reduce 是 JavaScript 数组的一个高阶函数，它对数组中的每个元素执行一个由你提供的“reducer”回调函数，将其结果汇总为单个返回值。reduce 函数的核心思想是将数组中的多个值“归约”为一个值。
reduce 函数的语法
array.reduce(reducerFunction, initialValue);
reducerFunction: 一个回调函数，它接收四个参数：accumulator: 累加器，它会累积回调函数的返回值。它是上一次回调函数返回的值，或者是initialValue（如果提供了）。currentValue: 当前正在处理的数组元素。currentIndex: 当前正在处理的数组元素的索引。array: 调用reduce的数组本身。
initialValue: 可选参数，作为第一次调用reducerFunction时accumulator的初始值。如果未提供，则使用数组的第一个元素作为初始值，并且会跳过第一个元素。
reduce 函数的工作原理
- 初始化:
- 如果提供了
initialValue，则accumulator初始化为initialValue，并且reducerFunction从数组的第一个元素开始执行。 - 如果没有提供
initialValue，则accumulator初始化为数组的第一个元素，并且reducerFunction从数组的第二个元素开始执行。
- 如果提供了
- 迭代:
reducerFunction会遍历数组中的每个元素（或从第二个元素开始，如果没有initialValue）。- 在每次迭代中，
reducerFunction会被调用，并接收accumulator、currentValue、currentIndex和array作为参数。 reducerFunction的返回值会成为下一次迭代的accumulator。
- 返回结果:
- 当数组中的所有元素都被处理完毕后，
reduce函数会返回最终的accumulator的值。
- 当数组中的所有元素都被处理完毕后，
reduce 函数的常见用途
- 求和: 计算数组中所有元素的总和。
- 求积: 计算数组中所有元素的乘积。
- 查找最大值/最小值: 找出数组中的最大值或最小值。
- 数组扁平化: 将多维数组转换为一维数组。
- 对象属性计数: 统计数组中对象属性的出现次数。
- 分组数据: 根据特定条件将数组中的元素分组。
- 管道操作: 将多个函数串联起来处理数据。
代码示例
涵盖了 reduce 函数的各种用途，并附有详细的注释。
// 1. 求和
function sumArray(arr) {
return arr.reduce((accumulator, currentValue) => accumulator + currentValue, 0);
}
const numbers = [1, 2, 3, 4, 5];
console.log("1. 求和:", sumArray(numbers)); // 输出: 15
// 2. 求积
function productArray(arr) {
return arr.reduce((accumulator, currentValue) => accumulator * currentValue, 1);
}
console.log("2. 求积:", productArray(numbers)); // 输出: 120
// 3. 查找最大值
function findMax(arr) {
return arr.reduce((accumulator, currentValue) => Math.max(accumulator, currentValue));
}
console.log("3. 查找最大值:", findMax(numbers)); // 输出: 5
// 4. 查找最小值
function findMin(arr) {
return arr.reduce((accumulator, currentValue) => Math.min(accumulator, currentValue));
}
console.log("4. 查找最小值:", findMin(numbers)); // 输出: 1
// 5. 数组扁平化
function flattenArray(arr) {
return arr.reduce((accumulator, currentValue) => {
return accumulator.concat(Array.isArray(currentValue) ? flattenArray(currentValue) : currentValue);
}, []);
}
const nestedArray = [1, [2, 3], [4, [5, 6]]];
console.log("5. 数组扁平化:", flattenArray(nestedArray)); // 输出: [1, 2, 3, 4, 5, 6]
// 6. 对象属性计数
function countProperties(arr, property) {
return arr.reduce((accumulator, currentValue) => {
if (currentValue.hasOwnProperty(property)) {
accumulator[currentValue[property]] = (accumulator[currentValue[property]] || 0) + 1;
}
return accumulator;
}, {});
}
const users = [
{ name: "Alice", city: "New York" },
{ name: "Bob", city: "London" },
{ name: "Charlie", city: "New York" },
{ name: "David", city: "Paris" },
{ name: "Eve", city: "London" },
];
console.log("6. 对象属性计数:", countProperties(users, "city")); // 输出: { 'New York': 2, London: 2, Paris: 1 }
// 7. 分组数据
function groupBy(arr, key) {
return arr.reduce((accumulator, currentValue) => {
const groupKey = currentValue[key];
if (!accumulator[groupKey]) {
accumulator[groupKey] = [];
}
accumulator[groupKey].push(currentValue);
return accumulator;
}, {});
}
console.log("7. 分组数据:", groupBy(users, "city"));
// 输出:
// {
// 'New York': [
// { name: 'Alice', city: 'New York' },
// { name: 'Charlie', city: 'New York' }
// ],
// London: [
// { name: 'Bob', city: 'London' },
// { name: 'Eve', city: 'London' }
// ],
// Paris: [ { name: 'David', city: 'Paris' } ]
// }
// 8. 管道操作
function pipe(...fns) {
return (initialValue) => fns.reduce((accumulator, fn) => fn(accumulator), initialValue);
}
function add(x) {
return x + 2;
}
function multiply(x) {
return x * 3;
}
function subtract(x) {
return x - 1;
}
const pipeline = pipe(add, multiply, subtract);
console.log("8. 管道操作:", pipeline(5)); // 输出: 20 ( (5 + 2) * 3 - 1 )
// 9. 字符串反转
function reverseString(str) {
return str.split("").reduce((accumulator, currentValue) => currentValue + accumulator, "");
}
console.log("9. 字符串反转:", reverseString("hello")); // 输出: olleh
// 10. 数组去重
function uniqueArray(arr) {
return arr.reduce((accumulator, currentValue) => {
if (!accumulator.includes(currentValue)) {
accumulator.push(currentValue);
}
return accumulator;
}, []);
}
const duplicateArray = [1, 2, 2, 3, 4, 4, 5];
console.log("10. 数组去重:", uniqueArray(duplicateArray)); // 输出: [1, 2, 3, 4, 5]
// 11. 处理异步操作 (Promise 串行执行)
async function asyncOperation(value) {
return new Promise((resolve) => {
setTimeout(() => {
resolve(value * 2);
}, 500);
});
}
async function processAsyncOperations(arr) {
return arr.reduce(async (accumulatorPromise, currentValue) => {
const accumulator = await accumulatorPromise;
const result = await asyncOperation(currentValue);
return accumulator.concat(result);
}, Promise.resolve([]));
}
async function runAsyncExample() {
const asyncNumbers = [1, 2, 3];
const results = await processAsyncOperations(asyncNumbers);
console.log("11. 处理异步操作:", results); // 输出: [2, 4, 6] (大约 1.5 秒后)
}
runAsyncExample();
// 12. 构建复杂的对象
function buildComplexObject(arr) {
return arr.reduce((accumulator, currentValue) => {
const [key, value] = currentValue;
const keys = key.split(".");
let current = accumulator;
for (let i = 0; i < keys.length - 1; i++) {
const k = keys[i];
if (!current[k]) {
current[k] = {};
}
current = current[k];
}
current[keys[keys.length - 1]] = value;
return accumulator;
}, {});
}
const data = [
["a.b.c", 1],
["a.b.d", 2],
["a.e", 3],
["f", 4],
];
console.log("12. 构建复杂的对象:", buildComplexObject(data));
// 输出:
// {
// a: { b: { c: 1, d: 2 }, e: 3 },
// f: 4
// }
// 13. 实现函数组合 (更灵活的 pipe)
function compose(...fns) {
return (initialValue) => fns.reduceRight((accumulator, fn) => fn(accumulator), initialValue);
}
const composedPipeline = compose(subtract, multiply, add);
console.log("13. 函数组合:", composedPipeline(5)); // 输出: 18 ( (5 + 2) * 3 - 1 )
// 14. 数据转换
function transformData(arr) {
return arr.reduce((accumulator, currentValue) => {
const { id, name, details } = currentValue;
const transformedDetails = details.map((detail) => ({
...detail,
full_name: `${name} - ${detail.description}`,
}));
accumulator[id] = {
name,
details: transformedDetails,
};
return accumulator;
}, {});
}
const rawData = [
{
id: 1,
name: "Product A",
details: [
{ description: "Detail 1", price: 10 },
{ description: "Detail 2", price: 20 },
],
},
{
id: 2,
name: "Product B",
details: [
{ description: "Detail 3", price: 30 },
{ description: "Detail 4", price: 40 },
],
},
];
console.log("14. 数据转换:", transformData(rawData));
// 输出:
// {
// '1': {
// name: 'Product A',
// details: [
// { description: 'Detail 1', price: 10, full_name: 'Product A - Detail 1' },
// { description: 'Detail 2', price: 20, full_name: 'Product A - Detail 2' }
// ]
// },
// '2': {
// name: 'Product B',
// details: [
// { description: 'Detail 3', price: 30, full_name: 'Product B - Detail 3' },
// { description: 'Detail 4', price: 40, full_name: 'Product B - Detail 4' }
// ]
// }
// }
// 15. 自定义累加器 (使用对象)
function customAccumulator(arr) {
return arr.reduce((accumulator, currentValue) => {
if (currentValue > 0) {
accumulator.positive.push(currentValue);
} else if (currentValue < 0) {
accumulator.negative.push(currentValue);
} else {
accumulator.zero.push(currentValue);
}
return accumulator;
}, { positive: [], negative: [], zero: [] });
}
const mixedNumbers = [-2, 1, 0, 3, -1, 0, 5];
console.log("15. 自定义累加器:", customAccumulator(mixedNumbers));
// 输出:
// { positive: [ 1, 3, 5 ], negative: [ -2, -1 ], zero: [ 0, 0 ] }
// 16. 使用 reduce 实现 map
function customMap(arr, callback) {
return arr.reduce((accumulator, currentValue, index, array) => {
accumulator.push(callback(currentValue, index, array));
return accumulator;
}, []);
}
const mapNumbers = [1, 2, 3, 4];
const mappedNumbers = customMap(mapNumbers, (num) => num * 2);
console.log("16. 使用 reduce 实现 map:", mappedNumbers); // 输出: [2, 4, 6, 8]
// 17. 使用 reduce 实现 filter
function customFilter(arr, callback) {
return arr.reduce((accumulator, currentValue, index, array) => {
if (callback(currentValue, index, array)) {
accumulator.push(currentValue);
}
return accumulator;
}, []);
}
const filterNumbers = [1, 2, 3, 4, 5, 6];
const filteredNumbers = customFilter(filterNumbers, (num) => num % 2 === 0);
console.log("17. 使用 reduce 实现 filter:", filteredNumbers); // 输出: [2, 4, 6]
// 18. 使用 reduce 实现 find
function customFind(arr, callback) {
return arr.reduce((accumulator, currentValue, index, array) => {
if (accumulator !== undefined) {
return accumulator;
}
if (callback(currentValue, index, array)) {
return currentValue;
}
return undefined;
}, undefined);
}
const findNumbers = [1, 2, 3, 4, 5];
const foundNumber = customFind(findNumbers, (num) => num > 3);
console.log("18. 使用 reduce 实现 find:", foundNumber); // 输出: 4
// 19. 使用 reduce 实现 findIndex
function customFindIndex(arr, callback) {
return arr.reduce((accumulator, currentValue, index, array) => {
if (accumulator !== -1) {
return accumulator;
}
if (callback(currentValue, index, array)) {
return index;
}
return -1;
}, -1);
}
const findIndexNumbers = [1, 2, 3, 4, 5];
const foundIndex = customFindIndex(findIndexNumbers, (num) => num > 3);
console.log("19. 使用 reduce 实现 findIndex:", foundIndex); // 输出: 3
// 20. 使用 reduce 实现 every
function customEvery(arr, callback) {
return arr.reduce((accumulator, currentValue, index, array) => {
return accumulator && callback(currentValue, index, array);
}, true);
}
const everyNumbers = [2, 4, 6, 8];
const allEven = customEvery(everyNumbers, (num) => num % 2 === 0);
console.log("20. 使用 reduce 实现 every:", allEven); // 输出: true
const notAllEvenNumbers = [2, 4, 5, 8];
const notAllEven = customEvery(notAllEvenNumbers, (num) => num % 2 === 0);
console.log("20. 使用 reduce 实现 every:", notAllEven); // 输出: false
// 21. 使用 reduce 实现 some
function customSome(arr, callback) {
return arr.reduce((accumulator, currentValue, index, array) => {
return accumulator || callback(currentValue, index, array);
}, false);
}
const someNumbers = [1, 3, 5, 8];
const hasEven = customSome(someNumbers, (num) => num % 2 === 0);
console.log("21. 使用 reduce 实现 some:", hasEven); // 输出: true
const noEvenNumbers = [1, 3, 5, 7];
const noEven = customSome(noEvenNumbers, (num) => num % 2 === 0);
console.log("21. 使用 reduce 实现 some:", noEven); // 输出: false
// 22. 使用 reduce 实现 flatMap
function customFlatMap(arr, callback) {
return arr.reduce((accumulator, currentValue, index, array) => {
return accumulator.concat(callback(currentValue, index, array));
}, []);
}
const flatMapNumbers = [1, 2, 3];
const flatMappedNumbers = customFlatMap(flatMapNumbers, (num) => [num, num * 2]);
console.log("22. 使用 reduce 实现 flatMap:", flatMappedNumbers); // 输出: [1, 2, 2, 4, 3, 6]
// 23. 使用 reduce 实现 reduceRight
function customReduceRight(arr, callback, initialValue) {
const reversedArr = [...arr].reverse();
return reversedArr.reduce(callback, initialValue);
}
const reduceRightNumbers = [1, 2, 3, 4];
const reducedRightResult = customReduceRight(reduceRightNumbers, (acc, curr) => acc - curr, 10);
console.log("23. 使用 reduce 实现 reduceRight:", reducedRightResult); // 输出: 0 (10 - 4 - 3 - 2 - 1)
// 24. 使用 reduce 实现 groupBy with custom key function
function customGroupBy(arr, keyFunction) {
return arr.reduce((accumulator, currentValue) => {
const key = keyFunction(currentValue);
if (!accumulator[key]) {
accumulator[key] = [];
}
accumulator[key].push(currentValue);
return accumulator;
}, {});
}
const customGroupUsers = [
{ name: "Alice", age: 25 },
{ name: "Bob", age: 30 },
{ name: "Charlie", age: 25 },
{ name: "David", age: 35 },
];
const groupedByAge = customGroupBy(customGroupUsers, (user) => user.age);
console.log("24. 使用 reduce 实现 groupBy with custom key function:", groupedByAge);
// 输出:
// {
// '25': [ { name: 'Alice', age: 25 }, { name: 'Charlie', age: 25 } ],
// '30': [ { name: 'Bob', age: 30 } ],
// '35': [ { name: 'David', age: 35 } ]
// }
// 25. 使用 reduce 实现 partition
function customPartition(arr, callback) {
return arr.reduce((accumulator, currentValue, index, array) => {
if (callback(currentValue, index, array)) {
accumulator[0].push(currentValue);
} else {
accumulator[1].push(currentValue);
}
return accumulator;
}, [[], []]);
}
const partitionNumbers = [1, 2, 3, 4, 5, 6];
const [evenNumbers, oddNumbers] = customPartition(partitionNumbers, (num) => num % 2 === 0);
console.log("25. 使用 reduce 实现 partition:", evenNumbers, oddNumbers); // 输出: [2, 4, 6] [1, 3, 5]
// 26. 使用 reduce 实现 chunk
function customChunk(arr, size) {
return arr.reduce((accumulator, currentValue, index) => {
const chunkIndex = Math.floor(index / size);
if (!accumulator[chunkIndex]) {
accumulator[chunkIndex] = [];
}
accumulator[chunkIndex].push(currentValue);
return accumulator;
}, []);
}
const chunkNumbers = [1, 2, 3, 4, 5, 6, 7, 8];
const chunkedNumbers = customChunk(chunkNumbers, 3);
console.log("26. 使用 reduce 实现 chunk:", chunkedNumbers); // 输出: [[1, 2, 3], [4, 5, 6], [7, 8]]
// 27. 使用 reduce 实现 zip
function customZip(...arrays) {
return arrays[0].reduce((accumulator, _, index) => {
const zipped = arrays.map(arr => arr[index]);
accumulator.push(zipped);
return accumulator;
}, []);
}
const zipArrays1 = [1, 2, 3];
const zipArrays2 = ['a', 'b', 'c'];
const zipArrays3 = [true, false, true];
const zippedArrays = customZip(zipArrays1, zipArrays2, zipArrays3);
console.log("27. 使用 reduce 实现 zip:", zippedArrays); // 输出: [[1, 'a', true], [2, 'b', false], [3, 'c', true]]
// 28. 使用 reduce 实现 unzip
function customUnzip(arr) {
if (!arr || arr.length === 0) {
return [];
}
const numArrays = arr[0].length;
return arr.reduce((accumulator, current) => {
current.forEach((value, index) => {
if (!accumulator[index]) {
accumulator[index] = [];
}
accumulator[index].push(value);
});
return accumulator;
}, Array.from({ length: numArrays }, () => []));
}
const unzipArrays = [[1, 'a', true], [2, 'b', false], [3, 'c', true]];
const unzippedArrays = customUnzip(unzipArrays);
console.log("28. 使用 reduce 实现 unzip:", unzippedArrays); // 输出: [[1, 2, 3], ['a', 'b', 'c'], [true, false, true]]
// 29. 使用 reduce 实现 countBy
function customCountBy(arr, keyFunction) {
return arr.reduce((accumulator, currentValue) => {
const key = keyFunction(currentValue);
accumulator[key] = (accumulator[key] || 0) + 1;
return accumulator;
}, {});
}
const countByUsers = [
{ name: "Alice", age: 25 },
{ name: "Bob", age: 30 },
{ name: "Charlie", age: 25 },
{ name: "David", age: 35 },
];
const countedByAge = customCountBy(countByUsers, (user) => user.age);
console.log("29. 使用 reduce 实现 countBy:", countedByAge); // 输出: { '25': 2, '30': 1, '35': 1 }
// 30. 使用 reduce 实现 sumBy
function customSumBy(arr, keyFunction) {
return arr.reduce((accumulator, currentValue) => {
const value = keyFunction(currentValue);
return accumulator + value;
}, 0);
}
const sumByUsers = [
{ name: "Alice", age: 25 },
{ name: "Bob", age: 30 },
{ name: "Charlie", age: 25 },
{ name: "David", age: 35 },
];
const sumOfAges = customSumBy(sumByUsers, (user) => user.age);
console.log("30. 使用 reduce 实现 sumBy:", sumOfAges); // 输出: 115
// 31. 使用 reduce 实现 minBy
function customMinBy(arr, keyFunction) {
return arr.reduce((accumulator, currentValue) => {
const currentKey = keyFunction(currentValue);
if (accumulator === undefined || currentKey < keyFunction(accumulator)) {
return currentValue;
}
return accumulator;
}, undefined);
}
const minByUsers = [
{ name: "Alice", age: 25 },
{ name: "Bob", age: 30 },
{ name: "Charlie", age: 20 },
{ name: "David", age: 35 },
];
const minAgeUser = customMinBy(minByUsers, (user) => user.age);
console.log("31. 使用 reduce 实现 minBy:", minAgeUser); // 输出: { name: 'Charlie', age: 20 }
// 32. 使用 reduce 实现 maxBy
function customMaxBy(arr, keyFunction) {
return arr.reduce((accumulator, currentValue) => {
const currentKey = keyFunction(currentValue);
if (accumulator === undefined || currentKey > keyFunction(accumulator)) {
return currentValue;
}
return accumulator;
}, undefined);
}
const maxByUsers = [
{ name: "Alice", age: 25 },
{ name: "Bob", age: 30 },
{ name: "Charlie", age: 20 },
{ name: "David", age: 35 },
];
const maxAgeUser = customMaxBy(maxByUsers, (user) => user.age);
console.log("32. 使用 reduce 实现 maxBy:", maxAgeUser); // 输出: { name: 'David', age: 35 }
// 33. 使用 reduce 实现 keyBy
function customKeyBy(arr, keyFunction) {
return arr.reduce((accumulator, currentValue) => {
const key = keyFunction(currentValue);
accumulator[key] = currentValue;
return accumulator;
}, {});
}
const keyByUsers = [
{ id: 1, name: "Alice" },
{ id: 2, name: "Bob" },
{ id: 3, name: "Charlie" },
];
const keyedById = customKeyBy(keyByUsers, (user) => user.id);
console.log("33. 使用 reduce 实现 keyBy:", keyedById);
// 输出:
// {
// '1': { id: 1, name: 'Alice' },
// '2': { id: 2, name: 'Bob' },
// '3': { id: 3, name: 'Charlie' }
// }
// 34. 使用 reduce 实现 flat
function customFlat(arr, depth = 1) {
return arr.reduce((accumulator, currentValue) => {
if (Array.isArray(currentValue) && depth > 0) {
return accumulator.concat(customFlat(currentValue, depth - 1));
}
return accumulator.concat(currentValue);
}, []);
}
const flatArray = [1, [2, [3, [4]], 5], 6];
const flattenedArray = customFlat(flatArray, 2);
console.log("34. 使用 reduce 实现 flat:", flattenedArray); // 输出: [1, 2, 3, [4], 5, 6]
const deeplyFlattenedArray = customFlat(flatArray, Infinity);
console.log("34. 使用 reduce 实现 flat (deep):", deeplyFlattenedArray); // 输出: [1, 2, 3, 4, 5, 6]
// 35. 使用 reduce 实现 intersection
function customIntersection(arr1, arr2) {
return arr1.reduce((accumulator, currentValue) => {
if (arr2.includes(currentValue)) {
accumulator.push(currentValue);
}
return accumulator;
}, []);
}
const intersectionArray1 = [1, 2, 3, 4, 5];
const intersectionArray2 = [3, 4, 5, 6, 7];
const intersectionResult = customIntersection(intersectionArray1, intersectionArray2);
console.log("35. 使用 reduce 实现 intersection:", intersectionResult); // 输出: [3, 4, 5]
// 36. 使用 reduce 实现 difference
function customDifference(arr1, arr2) {
return arr1.reduce((accumulator, currentValue) => {
if (!arr2.includes(currentValue)) {
accumulator.push(currentValue);
}
return accumulator;
}, []);
}
const differenceArray1 = [1, 2, 3, 4, 5];
const differenceArray2 = [3, 4, 5, 6, 7];
const differenceResult = customDifference(differenceArray1, differenceArray2);
console.log("36. 使用 reduce 实现 difference:", differenceResult); // 输出: [1, 2]
// 37. 使用 reduce 实现 union
function customUnion(arr1, arr2) {
return arr1.concat(arr2).reduce((accumulator, currentValue) => {
if (!accumulator.includes(currentValue)) {
accumulator.push(currentValue);
}
return accumulator;
}, []);
}
const unionArray1 = [1, 2, 3];
const unionArray2 = [3, 4, 5];
const unionResult = customUnion(unionArray1, unionArray2);
console.log("37. 使用 reduce 实现 union:", unionResult); // 输出: [1, 2, 3, 4, 5]
// 38. 使用 reduce 实现 symmetricDifference
function customSymmetricDifference(arr1, arr2) {
const diff1 = customDifference(arr1, arr2);
const diff2 = customDifference(arr2, arr1);
return customUnion(diff1, diff2);
}
const symmetricDifferenceArray1 = [1, 2, 3, 4];
const symmetricDifferenceArray2 = [3, 4, 5, 6];
const symmetricDifferenceResult = customSymmetricDifference(symmetricDifferenceArray1, symmetricDifferenceArray2);
console.log("38. 使用 reduce 实现 symmetricDifference:", symmetricDifferenceResult); // 输出: [1, 2, 5, 6]
// 39. 使用 reduce 实现 shuffle
function customShuffle(arr) {
return arr.reduce((accumulator, _, index) => {
const randomIndex = Math.floor(Math.random() * (index + 1));
[accumulator[index], accumulator[randomIndex]] = [accumulator[randomIndex], accumulator[index]];
return accumulator;
}, [...arr]);
}
const shuffleArray = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
const shuffledArray = customShuffle(shuffleArray);
console.log("39. 使用 reduce 实现 shuffle:", shuffledArray); // 输出: 随机排序的数组
// 40. 使用 reduce 实现 range
function customRange(start, end, step = 1) {
const length = Math.max(Math.ceil((end - start) / step), 0);
return Array.from({ length }, (_, index) => start + index * step);
}
const rangeArray = customRange(1, 10, 2);
console.log("40. 使用 reduce 实现 range:", rangeArray); // 输出: [1, 3, 5, 7, 9]
const rangeArray2 = customRange(10, 1, -2);
console.log("40. 使用 reduce 实现 range (reverse):", rangeArray2); // 输出: [10, 8, 6, 4, 2]
// 41. 使用 reduce 实现 fill
function customFill(arr, value, start = 0, end = arr.length) {
return arr.reduce((accumulator, currentValue, index) => {
if (index >= start && index < end) {
accumulator[index] = value;
}
return accumulator;
}, [...arr]);
}
const fillArray = [1, 2, 3, 4, 5];
const filledArray = customFill(fillArray, 0, 1, 4);
console.log("41. 使用 reduce 实现 fill:", filledArray); // 输出: [1, 0, 0, 0, 5]
// 42. 使用 reduce 实现 padStart
function customPadStart(str, targetLength, padString = ' ') {
if (str.length >= targetLength) {
return str;
}
const paddingLength = targetLength - str.length;
const padding = Array.from({ length: paddingLength }, () => padString).join('');
return padding + str;
}
const padStartString = "123";
const paddedStartString = customPadStart(padStartString, 5, '0');
console.log("42. 使用 reduce 实现 padStart:", paddedStartString); // 输出: "00123"
// 43. 使用 reduce 实现 padEnd
function customPadEnd(str, targetLength, padString = ' ') {
if (str.length >= targetLength) {
return str;
}
const paddingLength = targetLength - str.length;
const padding = Array.from({ length: paddingLength }, () => padString).join('');
return str + padding;
}
const padEndString = "123";
const paddedEndString = customPadEnd(padEndString, 5, '0');
console.log("43. 使用 reduce 实现 padEnd:", paddedEndString); // 输出: "12300"
// 44. 使用 reduce 实现 repeat
function customRepeat(str, count) {
return Array.from({ length: count }, () => str).join('');
}
const repeatString = "abc";
const repeatedString = customRepeat(repeatString, 3);
console.log("44. 使用 reduce 实现 repeat:", repeatedString); // 输出: "abcabcabc"
// 45. 使用 reduce 实现 trim
function customTrim(str) {
return str.reduce((accumulator, currentValue) => {
if (currentValue !== ' ') {
accumulator.push(currentValue);
}
return accumulator;
}, []).join('');
}
const trimString = " hello world ";
const trimmedString = customTrim(trimString.split(''));
console.log("45. 使用 reduce 实现 trim:", trimmedString); // 输出: "helloworld"
// 46. 使用 reduce 实现 trimStart
function customTrimStart(str) {
let trimmed = false;
return str.reduce((accumulator, currentValue) => {
if (!trimmed && currentValue === ' ') {
return accumulator;
}
trimmed = true;
accumulator.push(currentValue);
return accumulator;
}, []).join('');
}
const trimStartString = " hello world ";
const trimmedStartString = customTrimStart(trimStartString.split(''));
console.log("46. 使用 reduce 实现 trimStart:", trimmedStartString); // 输出: "hello world "
// 47. 使用 reduce 实现 trimEnd
function customTrimEnd(str) {
let trimmed = false;
return str.reduceRight((accumulator, currentValue) => {
if (!trimmed && currentValue === ' ') {
return accumulator;
}
trimmed = true;
accumulator.unshift(currentValue);
return accumulator;
}, []).join('');
}
const trimEndString = " hello world ";
const trimmedEndString = customTrimEnd(trimEndString.split(''));
console.log("47. 使用 reduce 实现 trimEnd:", trimmedEndString); // 输出: " hello world"
// 48. 使用 reduce 实现 startsWith
function customStartsWith(str, searchString, position = 0) {
return str.slice(position, position + searchString.length).reduce((accumulator, currentValue, index) => {
return accumulator && currentValue === searchString[index];
}, true);
}
const startsWithString = "hello world";
const startsWithResult = customStartsWith(startsWithString.split(''), "hello");
console.log("48. 使用 reduce 实现 startsWith:", startsWithResult); // 输出: true
const startsWithResult2 = customStartsWith(startsWithString.split(''), "world");
console.log("48. 使用 reduce 实现 startsWith (false):", startsWithResult2); // 输出: false
// 49. 使用 reduce 实现 endsWith
function customEndsWith(str, searchString, position = str.length) {
const start = Math.max(0, position - searchString.length);
return str.slice(start, position).reduce((accumulator, currentValue, index) => {
return accumulator && currentValue === searchString[index];
}, true);
}
const endsWithString = "hello world";
const endsWithResult = customEndsWith(endsWithString.split(''), "world");
console.log("49. 使用 reduce 实现 endsWith:", endsWithResult); // 输出: true
const endsWithResult2 = customEndsWith(endsWithString.split(''), "hello");
console.log("49. 使用 reduce 实现 endsWith (false):", endsWithResult2); // 输出: false
// 50. 使用 reduce 实现 includes
function customIncludes(arr, searchElement, fromIndex = 0) {
return arr.slice(fromIndex).reduce((accumulator, currentValue) => {
return accumulator || currentValue === searchElement;
}, false);
}
const includesArray = [1, 2, 3, 4, 5];
const includesResult = customIncludes(includesArray, 3);
console.log("50. 使用 reduce 实现 includes:", includesResult); // 输出: true
const includesResult2 = customIncludes(includesArray, 6);
console.log("50. 使用 reduce 实现 includes (false):", includesResult2); // 输出: false
// 51. 使用 reduce 实现 indexOf
function customIndexOf(arr, searchElement, fromIndex = 0) {
return arr.slice(fromIndex).reduce((accumulator, currentValue, index) => {
if (accumulator !== -1) {
return accumulator;
}
if (currentValue === searchElement) {
return index + fromIndex;
}
return -1;
}, -1);
}
const indexOfArray = [1, 2, 3, 4, 5, 3];
const indexOfResult = customIndexOf(indexOfArray, 3);
console.log("51. 使用 reduce 实现 indexOf:", indexOfResult); // 输出: 2
const indexOfResult2 = customIndexOf(indexOfArray, 6);
console.log("51. 使用 reduce 实现 indexOf (not found):", indexOfResult2); // 输出: -1
// 52. 使用 reduce 实现 lastIndexOf
function customLastIndexOf(arr, searchElement, fromIndex = arr.length - 1) {
return arr.slice(0, fromIndex + 1).reduceRight((accumulator, currentValue, index) => {
if (accumulator !== -1) {
return accumulator;
}
if (currentValue === searchElement) {
return index;
}
return -1;
}, -1);
}
const lastIndexOfArray = [1, 2, 3, 4, 5, 3];
const lastIndexOfResult = customLastIndexOf(lastIndexOfArray, 3);
console.log("52. 使用 reduce 实现 lastIndexOf:", lastIndexOfResult); // 输出: 5
const lastIndexOfResult2 = customLastIndexOf(lastIndexOfArray, 6);
console.log("52. 使用 reduce 实现 lastIndexOf (not found):", lastIndexOfResult2); // 输出: -1
// 53. 使用 reduce 实现 join
function customJoin(arr, separator = ',') {
return arr.reduce((accumulator, currentValue, index) => {
if (index === 0) {
return String(currentValue);
}
return accumulator + separator + String(currentValue);
}, '');
}
const joinArray = [1, 2, 3, 4, 5];
const joinedString = customJoin(joinArray, '-');
console.log("53. 使用 reduce 实现 join:", joinedString); // 输出: "1-2-3-4-5"
const joinedString2 = customJoin(joinArray);
console.log("53. 使用 reduce 实现 join (default separator):", joinedString2); // 输出: "1,2,3,4,5"
// 54. 使用 reduce 实现 reverse
function customReverse(arr) {
return arr.reduceRight((accumulator, currentValue) => {
accumulator.push(currentValue);
return accumulator;
}, []);
}
const reverseArray = [1, 2, 3, 4, 5];
const reversedArray = customReverse(reverseArray);
console.log("54. 使用 reduce 实现 reverse:", reversedArray); // 输出: [5, 4, 3, 2, 1]
// 55. 使用 reduce 实现 slice
function customSlice(arr, start = 0, end = arr.length) {
return arr.reduce((accumulator, currentValue, index) => {
if (index >= start && index < end) {
accumulator.push(currentValue);
}
return accumulator;
}, []);
}
const sliceArray = [1, 2, 3, 4, 5];
const slicedArray = customSlice(sliceArray, 1, 4);
console.log("55. 使用 reduce 实现 slice:", slicedArray); // 输出: [2, 3, 4]
const slicedArray2 = customSlice(sliceArray, 2);
console.log("55. 使用 reduce 实现 slice (from start):", slicedArray2); // 输出: [3, 4, 5]
// 56. 使用 reduce 实现 splice
function customSplice(arr, start, deleteCount, ...items) {
const deleted = [];
const result = arr.reduce((accumulator, currentValue, index) => {
if (index < start || index >= start + deleteCount) {
accumulator.push(currentValue);
} else {
deleted.push(currentValue);
}
return accumulator;
}, []);
result.splice(start, 0, ...items);
return { result, deleted };
}
const spliceArray = [1, 2, 3, 4, 5];
const { result: splicedResult, deleted: splicedDeleted } = customSplice(spliceArray, 1, 2, 6, 7);
console.log("56. 使用 reduce 实现 splice:", splicedResult, splicedDeleted); // 输出: [1, 6, 7, 4, 5] [2, 3]
const spliceArray2 = [1, 2, 3, 4, 5];
const { result: splicedResult2, deleted: splicedDeleted2 } = customSplice(spliceArray2, 2, 0, 6, 7);
console.log("56. 使用 reduce 实现 splice (insert):", splicedResult2, splicedDeleted2); // 输出: [1, 2, 6, 7, 3, 4, 5] []
// 57. 使用 reduce 实现 toReversed
function customToReversed(arr) {
return arr.reduceRight((accumulator, currentValue) => {
accumulator.push(currentValue);
return accumulator;
}, []);
}
const toReversedArray = [1, 2, 3, 4, 5];
const reversedArray2 = customToReversed(toReversedArray);
console.log("57. 使用 reduce 实现 toReversed:", reversedArray2); // 输出: [5, 4, 3, 2, 1]
// 58. 使用 reduce 实现 toSorted
function customToSorted(arr, compareFn) {
return [...arr].reduce((accumulator, currentValue) => {
let i = 0;
while (i < accumulator.length && (compareFn ? compareFn(currentValue, accumulator[i]) > 0 : String(currentValue) > String(accumulator[i]))) {
i++;
}
accumulator.splice(i, 0, currentValue);
return accumulator;
}, []);
}
const toSortedArray = [3, 1, 4, 2, 5];
const sortedArray = customToSorted(toSortedArray);
console.log("58. 使用 reduce 实现 toSorted:", sortedArray); // 输出: [1, 2, 3, 4, 5]
const toSortedArray2 = [3, 1, 4, 2, 5];
const sortedArray2 = customToSorted(toSortedArray2, (a, b) => b - a);
console.log("58. 使用 reduce 实现 toSorted (descending):", sortedArray2); // 输出: [5, 4, 3, 2, 1]
// 59. 使用 reduce 实现 toSpliced
function customToSpliced(arr, start, deleteCount, ...items) {
const result = [...arr].reduce((accumulator, currentValue, index) => {
if (index < start || index >= start + deleteCount) {
accumulator.push(currentValue);
}
return accumulator;
}, []);
result.splice(start, 0, ...items);
return result;
}
const toSplicedArray = [1, 2, 3, 4, 5];
const splicedArray3 = customToSpliced(toSplicedArray, 1, 2, 6, 7);
console.log("59. 使用 reduce 实现 toSpliced:", splicedArray3); // 输出: [1, 6, 7, 4, 5]
const toSplicedArray2 = [1, 2, 3, 4, 5];
const splicedArray4 = customToSpliced(toSplicedArray2, 2, 0, 6, 7);
console.log("59. 使用 reduce 实现 toSpliced (insert):", splicedArray4); // 输出: [1, 2, 6, 7, 3, 4, 5]
// 60. 使用 reduce 实现 with
function customWith(arr, index, value) {
return arr.reduce((accumulator, currentValue, currentIndex) => {
if (currentIndex === index) {
accumulator.push(value);
} else {
accumulator.push(currentValue);
}
return accumulator;
}, []);
}
const withArray = [1, 2, 3, 4, 5];
const withResult = customWith(withArray, 2, 6);
console.log("60. 使用 reduce 实现 with:", withResult); // 输出: [1, 2, 6, 4, 5]
// 61. 使用 reduce 实现 findLast
function customFindLast(arr, callback) {
return arr.reduceRight((accumulator, currentValue, index, array) => {
if (accumulator !== undefined) {
return accumulator;
}
if (callback(currentValue, index, array)) {
return currentValue;
}
return undefined;
}, undefined);
}
const findLastArray = [1, 2, 3, 4, 5, 3];
const findLastResult = customFindLast(findLastArray, (num) => num === 3);
console.log("61. 使用 reduce 实现 findLast:", findLastResult); // 输出: 3
const findLastResult2 = customFindLast(findLastArray, (num) => num > 5);
console.log("61. 使用 reduce 实现 findLast (not found):", findLastResult2); // 输出: undefined
// 62. 使用 reduce 实现 findLastIndex
function customFindLastIndex(arr, callback) {
return arr.reduceRight((accumulator, currentValue, index, array) => {
if (accumulator !== -1) {
return accumulator;
}
if (callback(currentValue, index, array)) {
return index;
}
return -1;
}, -1);
}
const findLastIndexArray = [1, 2, 3, 4, 5, 3];
const findLastIndexResult = customFindLastIndex(findLastIndexArray, (num) => num === 3);
console.log("62. 使用 reduce 实现 findLastIndex:", findLastIndexResult); // 输出: 5
const findLastIndexResult2 = customFindLastIndex(findLastIndexArray, (num) => num > 5);
console.log("62. 使用 reduce 实现 findLastIndex (not found):", findLastIndexResult2); // 输出: -1
// 63. 使用 reduce 实现 flatMap with depth
function customFlatMapWithDepth(arr, callback, depth = 1) {
return arr.reduce((accumulator, currentValue, index, array) => {
const mappedValue = callback(currentValue, index, array);
if (Array.isArray(mappedValue) && depth > 0) {
return accumulator.concat(customFlatMapWithDepth(mappedValue, (x) => x, depth - 1));
}
return accumulator.concat(mappedValue);
}, []);
}
const flatMapWithDepthArray = [1, 2, 3];
const flatMapWithDepthResult = customFlatMapWithDepth(flatMapWithDepthArray, (num) => [num, [num * 2]], 2);
console.log("63. 使用 reduce 实现 flatMap with depth:", flatMapWithDepthResult); // 输出: [1, [2], 2, [4], 3, [6]]
const flatMapWithDepthResult2 = customFlatMapWithDepth(flatMapWithDepthArray, (num) => [num, [num * 2]], 1);
console.log("63. 使用 reduce 实现 flatMap with depth (depth 1):", flatMapWithDepthResult2); // 输出: [1, [2], 2, [4], 3, [6]]
// 64. 使用 reduce 实现 reduce with index
function customReduceWithIndex(arr, callback, initialValue) {
return arr.reduce((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const reduceWithIndexArray = [1, 2, 3, 4, 5];
const reduceWithIndexResult = customReduceWithIndex(reduceWithIndexArray, (acc, curr, index) => acc + curr + index, 0);
console.log("64. 使用 reduce 实现 reduce with index:", reduceWithIndexResult); // 输出: 20 (1+0 + 2+1 + 3+2 + 4+3 + 5+4)
// 65. 使用 reduce 实现 reduceRight with index
function customReduceRightWithIndex(arr, callback, initialValue) {
return arr.reduceRight((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const reduceRightWithIndexArray = [1, 2, 3, 4, 5];
const reduceRightWithIndexResult = customReduceRightWithIndex(reduceRightWithIndexArray, (acc, curr, index) => acc + curr + index, 0);
console.log("65. 使用 reduce 实现 reduceRight with index:", reduceRightWithIndexResult); // 输出: 20 (5+4 + 4+3 + 3+2 + 2+1 + 1+0)
// 66. 使用 reduce 实现 forEach
function customForEach(arr, callback) {
arr.reduce((_, currentValue, index, array) => {
callback(currentValue, index, array);
return undefined;
}, undefined);
}
const forEachArray = [1, 2, 3];
customForEach(forEachArray, (num, index) => console.log(`forEach: index ${index}, value ${num}`));
// 输出:
// forEach: index 0, value 1
// forEach: index 1, value 2
// forEach: index 2, value 3
// 67. 使用 reduce 实现 some with index
function customSomeWithIndex(arr, callback) {
return arr.reduce((accumulator, currentValue, index, array) => {
return accumulator || callback(currentValue, index, array);
}, false);
}
const someWithIndexArray = [1, 3, 5, 8];
const hasEvenWithIndex = customSomeWithIndex(someWithIndexArray, (num, index) => num % 2 === 0 && index > 0);
console.log("67. 使用 reduce 实现 some with index:", hasEvenWithIndex); // 输出: true
const noEvenWithIndexArray = [1, 3, 5, 7];
const noEvenWithIndex = customSomeWithIndex(noEvenWithIndexArray, (num, index) => num % 2 === 0 && index > 0);
console.log("67. 使用 reduce 实现 some with index (false):", noEvenWithIndex); // 输出: false
// 68. 使用 reduce 实现 every with index
function customEveryWithIndex(arr, callback) {
return arr.reduce((accumulator, currentValue, index, array) => {
return accumulator && callback(currentValue, index, array);
}, true);
}
const everyWithIndexArray = [2, 4, 6, 8];
const allEvenWithIndex = customEveryWithIndex(everyWithIndexArray, (num, index) => num % 2 === 0 && index > 0);
console.log("68. 使用 reduce 实现 every with index:", allEvenWithIndex); // 输出: true
const notAllEvenWithIndexArray = [2, 4, 5, 8];
const notAllEvenWithIndex = customEveryWithIndex(notAllEvenWithIndexArray, (num, index) => num % 2 === 0 && index > 0);
console.log("68. 使用 reduce 实现 every with index (false):", notAllEvenWithIndex); // 输出: false
// 69. 使用 reduce 实现 map with index
function customMapWithIndex(arr, callback) {
return arr.reduce((accumulator, currentValue, index, array) => {
accumulator.push(callback(currentValue, index, array));
return accumulator;
}, []);
}
const mapWithIndexArray = [1, 2, 3, 4];
const mappedWithIndex = customMapWithIndex(mapWithIndexArray, (num, index) => num * 2 + index);
console.log("69. 使用 reduce 实现 map with index:", mappedWithIndex); // 输出: [2, 5, 8, 11]
// 70. 使用 reduce 实现 filter with index
function customFilterWithIndex(arr, callback) {
return arr.reduce((accumulator, currentValue, index, array) => {
if (callback(currentValue, index, array)) {
accumulator.push(currentValue);
}
return accumulator;
}, []);
}
const filterWithIndexArray = [1, 2, 3, 4, 5, 6];
const filteredWithIndex = customFilterWithIndex(filterWithIndexArray, (num, index) => num % 2 === 0 && index > 0);
console.log("70. 使用 reduce 实现 filter with index:", filteredWithIndex); // 输出: [2, 4, 6]
// 71. 使用 reduce 实现 find with index
function customFindWithIndex(arr, callback) {
return arr.reduce((accumulator, currentValue, index, array) => {
if (accumulator !== undefined) {
return accumulator;
}
if (callback(currentValue, index, array)) {
return currentValue;
}
return undefined;
}, undefined);
}
const findWithIndexArray = [1, 2, 3, 4, 5];
const foundWithIndex = customFindWithIndex(findWithIndexArray, (num, index) => num > 3 && index > 0);
console.log("71. 使用 reduce 实现 find with index:", foundWithIndex); // 输出: 4
const findWithIndexResult2 = customFindWithIndex(findWithIndexArray, (num, index) => num > 5 && index > 0);
console.log("71. 使用 reduce 实现 find with index (not found):", findWithIndexResult2); // 输出: undefined
// 72. 使用 reduce 实现 findIndex with index
function customFindIndexWithIndex(arr, callback) {
return arr.reduce((accumulator, currentValue, index, array) => {
if (accumulator !== -1) {
return accumulator;
}
if (callback(currentValue, index, array)) {
return index;
}
return -1;
}, -1);
}
const findIndexWithIndexArray = [1, 2, 3, 4, 5];
const foundIndexWithIndex = customFindIndexWithIndex(findIndexWithIndexArray, (num, index) => num > 3 && index > 0);
console.log("72. 使用 reduce 实现 findIndex with index:", foundIndexWithIndex); // 输出: 3
const findIndexWithIndexResult2 = customFindIndexWithIndex(findIndexWithIndexArray, (num, index) => num > 5 && index > 0);
console.log("72. 使用 reduce 实现 findIndex with index (not found):", findIndexWithIndexResult2); // 输出: -1
// 73. 使用 reduce 实现 findLast with index
function customFindLastWithIndex(arr, callback) {
return arr.reduceRight((accumulator, currentValue, index, array) => {
if (accumulator !== undefined) {
return accumulator;
}
if (callback(currentValue, index, array)) {
return currentValue;
}
return undefined;
}, undefined);
}
const findLastWithIndexArray = [1, 2, 3, 4, 5, 3];
const findLastWithIndexResult = customFindLastWithIndex(findLastWithIndexArray, (num, index) => num === 3 && index < 5);
console.log("73. 使用 reduce 实现 findLast with index:", findLastWithIndexResult); // 输出: 3
const findLastWithIndexResult2 = customFindLastWithIndex(findLastWithIndexArray, (num, index) => num > 5 && index < 5);
console.log("73. 使用 reduce 实现 findLast with index (not found):", findLastWithIndexResult2); // 输出: undefined
// 74. 使用 reduce 实现 findLastIndex with index
function customFindLastIndexWithIndex(arr, callback) {
return arr.reduceRight((accumulator, currentValue, index, array) => {
if (accumulator !== -1) {
return accumulator;
}
if (callback(currentValue, index, array)) {
return index;
}
return -1;
}, -1);
}
const findLastIndexWithIndexArray = [1, 2, 3, 4, 5, 3];
const findLastIndexWithIndexResult = customFindLastIndexWithIndex(findLastIndexWithIndexArray, (num, index) => num === 3 && index < 5);
console.log("74. 使用 reduce 实现 findLastIndex with index:", findLastIndexWithIndexResult); // 输出: 2
const findLastIndexWithIndexResult2 = customFindLastIndexWithIndex(findLastIndexWithIndexArray, (num, index) => num > 5 && index < 5);
console.log("74. 使用 reduce 实现 findLastIndex with index (not found):", findLastIndexWithIndexResult2); // 输出: -1
// 75. 使用 reduce 实现 flatMap with index
function customFlatMapWithIndex(arr, callback) {
return arr.reduce((accumulator, currentValue, index, array) => {
return accumulator.concat(callback(currentValue, index, array));
}, []);
}
const flatMapWithIndexArray = [1, 2, 3];
const flatMappedWithIndex = customFlatMapWithIndex(flatMapWithIndexArray, (num, index) => [num, num * 2 + index]);
console.log("75. 使用 reduce 实现 flatMap with index:", flatMappedWithIndex); // 输出: [1, 2, 2, 5, 3, 8]
// 76. 使用 reduce 实现 flatMap with index and depth
function customFlatMapWithIndexAndDepth(arr, callback, depth = 1) {
return arr.reduce((accumulator, currentValue, index, array) => {
const mappedValue = callback(currentValue, index, array);
if (Array.isArray(mappedValue) && depth > 0) {
return accumulator.concat(customFlatMapWithIndexAndDepth(mappedValue, (x, i) => x, depth - 1));
}
return accumulator.concat(mappedValue);
}, []);
}
const flatMapWithIndexAndDepthArray = [1, 2, 3];
const flatMappedWithIndexAndDepth = customFlatMapWithIndexAndDepth(flatMapWithIndexAndDepthArray, (num, index) => [num, [num * 2 + index]], 2);
console.log("76. 使用 reduce 实现 flatMap with index and depth:", flatMappedWithIndexAndDepth); // 输出: [1, [2], 2, [5], 3, [8]]
const flatMappedWithIndexAndDepth2 = customFlatMapWithIndexAndDepth(flatMapWithIndexAndDepthArray, (num, index) => [num, [num * 2 + index]], 1);
console.log("76. 使用 reduce 实现 flatMap with index and depth (depth 1):", flatMappedWithIndexAndDepth2); // 输出: [1, [2], 2, [5], 3, [8]]
// 77. 使用 reduce 实现 reduce with initial value as object
function customReduceWithObjectInitialValue(arr, callback, initialValue) {
return arr.reduce((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const reduceWithObjectInitialValueArray = [1, 2, 3];
const reduceWithObjectInitialValueResult = customReduceWithObjectInitialValue(reduceWithObjectInitialValueArray, (acc, curr, index) => {
acc.sum += curr;
acc.count++;
return acc;
}, { sum: 0, count: 0 });
console.log("77. 使用 reduce 实现 reduce with initial value as object:", reduceWithObjectInitialValueResult); // 输出: { sum: 6, count: 3 }
// 78. 使用 reduce 实现 reduceRight with initial value as object
function customReduceRightWithObjectInitialValue(arr, callback, initialValue) {
return arr.reduceRight((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const reduceRightWithObjectInitialValueArray = [1, 2, 3];
const reduceRightWithObjectInitialValueResult = customReduceRightWithObjectInitialValue(reduceRightWithObjectInitialValueArray, (acc, curr, index) => {
acc.sum += curr;
acc.count++;
return acc;
}, { sum: 0, count: 0 });
console.log("78. 使用 reduce 实现 reduceRight with initial value as object:", reduceRightWithObjectInitialValueResult); // 输出: { sum: 6, count: 3 }
// 79. 使用 reduce 实现 reduce with initial value as array
function customReduceWithArrayInitialValue(arr, callback, initialValue) {
return arr.reduce((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const reduceWithArrayInitialValueArray = [1, 2, 3];
const reduceWithArrayInitialValueResult = customReduceWithArrayInitialValue(reduceWithArrayInitialValueArray, (acc, curr, index) => {
acc.push(curr * 2);
return acc;
}, []);
console.log("79. 使用 reduce 实现 reduce with initial value as array:", reduceWithArrayInitialValueResult); // 输出: [2, 4, 6]
// 80. 使用 reduce 实现 reduceRight with initial value as array
function customReduceRightWithArrayInitialValue(arr, callback, initialValue) {
return arr.reduceRight((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const reduceRightWithArrayInitialValueArray = [1, 2, 3];
const reduceRightWithArrayInitialValueResult = customReduceRightWithArrayInitialValue(reduceRightWithArrayInitialValueArray, (acc, curr, index) => {
acc.push(curr * 2);
return acc;
}, []);
console.log("80. 使用 reduce 实现 reduceRight with initial value as array:", reduceRightWithArrayInitialValueResult); // 输出: [6, 4, 2]
// 81. 使用 reduce 实现 reduce with initial value as string
function customReduceWithStringInitialValue(arr, callback, initialValue) {
return arr.reduce((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const reduceWithStringInitialValueArray = ['a', 'b', 'c'];
const reduceWithStringInitialValueResult = customReduceWithStringInitialValue(reduceWithStringInitialValueArray, (acc, curr) => acc + curr, '');
console.log("81. 使用 reduce 实现 reduce with initial value as string:", reduceWithStringInitialValueResult); // 输出: "abc"
// 82. 使用 reduce 实现 reduceRight with initial value as string
function customReduceRightWithStringInitialValue(arr, callback, initialValue) {
return arr.reduceRight((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const reduceRightWithStringInitialValueArray = ['a', 'b', 'c'];
const reduceRightWithStringInitialValueResult = customReduceRightWithStringInitialValue(reduceRightWithStringInitialValueArray, (acc, curr) => acc + curr, '');
console.log("82. 使用 reduce 实现 reduceRight with initial value as string:", reduceRightWithStringInitialValueResult); // 输出: "cba"
// 83. 使用 reduce 实现 reduce with initial value as number
function customReduceWithNumberInitialValue(arr, callback, initialValue) {
return arr.reduce((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const reduceWithNumberInitialValueArray = [1, 2, 3];
const reduceWithNumberInitialValueResult = customReduceWithNumberInitialValue(reduceWithNumberInitialValueArray, (acc, curr) => acc + curr, 0);
console.log("83. 使用 reduce 实现 reduce with initial value as number:", reduceWithNumberInitialValueResult); // 输出: 6
// 84. 使用 reduce 实现 reduceRight with initial value as number
function customReduceRightWithNumberInitialValue(arr, callback, initialValue) {
return arr.reduceRight((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const reduceRightWithNumberInitialValueArray = [1, 2, 3];
const reduceRightWithNumberInitialValueResult = customReduceRightWithNumberInitialValue(reduceRightWithNumberInitialValueArray, (acc, curr) => acc + curr, 0);
console.log("84. 使用 reduce 实现 reduceRight with initial value as number:", reduceRightWithNumberInitialValueResult); // 输出: 6
// 85. 使用 reduce 实现 reduce with initial value as boolean
function customReduceWithBooleanInitialValue(arr, callback, initialValue) {
return arr.reduce((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const reduceWithBooleanInitialValueArray = [true, true, false];
const reduceWithBooleanInitialValueResult = customReduceWithBooleanInitialValue(reduceWithBooleanInitialValueArray, (acc, curr) => acc && curr, true);
console.log("85. 使用 reduce 实现 reduce with initial value as boolean:", reduceWithBooleanInitialValueResult); // 输出: false
const reduceWithBooleanInitialValueResult2 = customReduceWithBooleanInitialValue([true, true, true], (acc, curr) => acc && curr, true);
console.log("85. 使用 reduce 实现 reduce with initial value as boolean (true):", reduceWithBooleanInitialValueResult2); // 输出: true
// 86. 使用 reduce 实现 reduceRight with initial value as boolean
function customReduceRightWithBooleanInitialValue(arr, callback, initialValue) {
return arr.reduceRight((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const reduceRightWithBooleanInitialValueArray = [true, true, false];
const reduceRightWithBooleanInitialValueResult = customReduceRightWithBooleanInitialValue(reduceRightWithBooleanInitialValueArray, (acc, curr) => acc && curr, true);
console.log("86. 使用 reduce 实现 reduceRight with initial value as boolean:", reduceRightWithBooleanInitialValueResult); // 输出: false
const reduceRightWithBooleanInitialValueResult2 = customReduceRightWithBooleanInitialValue([true, true, true], (acc, curr) => acc && curr, true);
console.log("86. 使用 reduce 实现 reduceRight with initial value as boolean (true):", reduceRightWithBooleanInitialValueResult2); // 输出: true
// 87. 使用 reduce 实现 reduce with initial value as null
function customReduceWithNullInitialValue(arr, callback, initialValue) {
return arr.reduce((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const reduceWithNullInitialValueArray = [1, 2, 3];
const reduceWithNullInitialValueResult = customReduceWithNullInitialValue(reduceWithNullInitialValueArray, (acc, curr) => acc === null ? curr : acc + curr, null);
console.log("87. 使用 reduce 实现 reduce with initial value as null:", reduceWithNullInitialValueResult); // 输出: 6
// 88. 使用 reduce 实现 reduceRight with initial value as null
function customReduceRightWithNullInitialValue(arr, callback, initialValue) {
return arr.reduceRight((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const reduceRightWithNullInitialValueArray = [1, 2, 3];
const reduceRightWithNullInitialValueResult = customReduceRightWithNullInitialValue(reduceRightWithNullInitialValueArray, (acc, curr) => acc === null ? curr : acc + curr, null);
console.log("88. 使用 reduce 实现 reduceRight with initial value as null:", reduceRightWithNullInitialValueResult); // 输出: 6
// 89. 使用 reduce 实现 reduce with initial value as undefined
function customReduceWithUndefinedInitialValue(arr, callback, initialValue) {
return arr.reduce((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const reduceWithUndefinedInitialValueArray = [1, 2, 3];
const reduceWithUndefinedInitialValueResult = customReduceWithUndefinedInitialValue(reduceWithUndefinedInitialValueArray, (acc, curr) => acc === undefined ? curr : acc + curr, undefined);
console.log("89. 使用 reduce 实现 reduce with initial value as undefined:", reduceWithUndefinedInitialValueResult); // 输出: 6
// 90. 使用 reduce 实现 reduceRight with initial value as undefined
function customReduceRightWithUndefinedInitialValue(arr, callback, initialValue) {
return arr.reduceRight((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const reduceRightWithUndefinedInitialValueArray = [1, 2, 3];
const reduceRightWithUndefinedInitialValueResult = customReduceRightWithUndefinedInitialValue(reduceRightWithUndefinedInitialValueArray, (acc, curr) => acc === undefined ? curr : acc + curr, undefined);
console.log("90. 使用 reduce 实现 reduceRight with initial value as undefined:", reduceRightWithUndefinedInitialValueResult); // 输出: 6
// 91. 使用 reduce 实现 reduce with initial value as symbol
function customReduceWithSymbolInitialValue(arr, callback, initialValue) {
return arr.reduce((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const symbol1 = Symbol('test');
const symbol2 = Symbol('test2');
const reduceWithSymbolInitialValueArray = [symbol1, symbol2];
const reduceWithSymbolInitialValueResult = customReduceWithSymbolInitialValue(reduceWithSymbolInitialValueArray, (acc, curr) => acc === null ? curr : acc, null);
console.log("91. 使用 reduce 实现 reduce with initial value as symbol:", reduceWithSymbolInitialValueResult); // 输出: Symbol(test)
// 92. 使用 reduce 实现 reduceRight with initial value as symbol
function customReduceRightWithSymbolInitialValue(arr, callback, initialValue) {
return arr.reduceRight((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const symbol3 = Symbol('test3');
const symbol4 = Symbol('test4');
const reduceRightWithSymbolInitialValueArray = [symbol3, symbol4];
const reduceRightWithSymbolInitialValueResult = customReduceRightWithSymbolInitialValue(reduceRightWithSymbolInitialValueArray, (acc, curr) => acc === null ? curr : acc, null);
console.log("92. 使用 reduce 实现 reduceRight with initial value as symbol:", reduceRightWithSymbolInitialValueResult); // 输出: Symbol(test3)
// 93. 使用 reduce 实现 reduce with initial value as function
function customReduceWithFunctionInitialValue(arr, callback, initialValue) {
return arr.reduce((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const func1 = () => 1;
const func2 = () => 2;
const reduceWithFunctionInitialValueArray = [func1, func2];
const reduceWithFunctionInitialValueResult = customReduceWithFunctionInitialValue(reduceWithFunctionInitialValueArray, (acc, curr) => acc === null ? curr : () => acc() + curr(), null);
console.log("93. 使用 reduce 实现 reduce with initial value as function:", reduceWithFunctionInitialValueResult()); // 输出: 3
// 94. 使用 reduce 实现 reduceRight with initial value as function
function customReduceRightWithFunctionInitialValue(arr, callback, initialValue) {
return arr.reduceRight((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const func3 = () => 3;
const func4 = () => 4;
const reduceRightWithFunctionInitialValueArray = [func3, func4];
const reduceRightWithFunctionInitialValueResult = customReduceRightWithFunctionInitialValue(reduceRightWithFunctionInitialValueArray, (acc, curr) => acc === null ? curr : () => acc() + curr(), null);
console.log("94. 使用 reduce 实现 reduceRight with initial value as function:", reduceRightWithFunctionInitialValueResult()); // 输出: 7
// 95. 使用 reduce 实现 reduce with initial value as date
function customReduceWithDateInitialValue(arr, callback, initialValue) {
return arr.reduce((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const date1 = new Date('2024-01-01');
const date2 = new Date('2024-01-02');
const reduceWithDateInitialValueArray = [date1, date2];
const reduceWithDateInitialValueResult = customReduceWithDateInitialValue(reduceWithDateInitialValueArray, (acc, curr) => acc === null ? curr : new Date(acc.getTime() + curr.getTime()), null);
console.log("95. 使用 reduce 实现 reduce with initial value as date:", reduceWithDateInitialValueResult); // 输出: 2024-01-03T00:00:00.000Z
// 96. 使用 reduce 实现 reduceRight with initial value as date
function customReduceRightWithDateInitialValue(arr, callback, initialValue) {
return arr.reduceRight((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const date3 = new Date('2024-01-03');
const date4 = new Date('2024-01-04');
const reduceRightWithDateInitialValueArray = [date3, date4];
const reduceRightWithDateInitialValueResult = customReduceRightWithDateInitialValue(reduceRightWithDateInitialValueArray, (acc, curr) => acc === null ? curr : new Date(acc.getTime() + curr.getTime()), null);
console.log("96. 使用 reduce 实现 reduceRight with initial value as date:", reduceRightWithDateInitialValueResult); // 输出: 2024-01-07T00:00:00.000Z
// 97. 使用 reduce 实现 reduce with initial value as regex
function customReduceWithRegexInitialValue(arr, callback, initialValue) {
return arr.reduce((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const regex1 = /a/g;
const regex2 = /b/g;
const reduceWithRegexInitialValueArray = [regex1, regex2];
const reduceWithRegexInitialValueResult = customReduceWithRegexInitialValue(reduceWithRegexInitialValueArray, (acc, curr) => acc === null ? curr : new RegExp(acc.source + curr.source, 'g'), null);
console.log("97. 使用 reduce 实现 reduce with initial value as regex:", reduceWithRegexInitialValueResult); // 输出: /ab/g
// 98. 使用 reduce 实现 reduceRight with initial value as regex
function customReduceRightWithRegexInitialValue(arr, callback, initialValue) {
return arr.reduceRight((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const regex3 = /c/g;
const regex4 = /d/g;
const reduceRightWithRegexInitialValueArray = [regex3, regex4];
const reduceRightWithRegexInitialValueResult = customReduceRightWithRegexInitialValue(reduceRightWithRegexInitialValueArray, (acc, curr) => acc === null ? curr : new RegExp(acc.source + curr.source, 'g'), null);
console.log("98. 使用 reduce 实现 reduceRight with initial value as regex:", reduceRightWithRegexInitialValueResult); // 输出: /dc/g
// 99. 使用 reduce 实现 reduce with initial value as set
function customReduceWithSetInitialValue(arr, callback, initialValue) {
return arr.reduce((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const set1 = new Set([1, 2]);
const set2 = new Set([3, 4]);
const reduceWithSetInitialValueArray = [set1, set2];
const reduceWithSetInitialValueResult = customReduceWithSetInitialValue(reduceWithSetInitialValueArray, (acc, curr) => {
if (acc === null) return curr;
curr.forEach(item => acc.add(item));
return acc;
}, null);
console.log("99. 使用 reduce 实现 reduce with initial value as set:", reduceWithSetInitialValueResult); // 输出: Set(4) {1, 2, 3, 4}
// 100. 使用 reduce 实现 reduceRight with initial value as set
function customReduceRightWithSetInitialValue(arr, callback, initialValue) {
return arr.reduceRight((accumulator, currentValue, index, array) => {
return callback(accumulator, currentValue, index, array);
}, initialValue);
}
const set3 = new Set([5, 6]);
const set4 = new Set([7, 8]);
const reduceRightWithSetInitialValueArray = [set3, set4];
const reduceRightWithSetInitialValueResult = customReduceRightWithSetInitialValue(reduceRightWithSetInitialValueArray, (acc, curr) => {
if (acc === null) return curr;
curr.forEach(item => acc.add(item));
return acc;
}, null);
console.log("100. 使用 reduce 实现 reduceRight with initial value as set:", reduceRightWithSetInitialValueResult); // 输出: Set(4) {5, 6, 7, 8}
