通过示例解释所有 JavaScript 数组方法
作为一名程序员，我们的工作是写有效的代码，但是仅仅写有效的代码，这还不够。如果想成为优秀的程序员，我们还需要编写可维护和可扩展的代码。
const names = ["Jhon", "Bob", "Alice", "Joe"];const nameAtIndex1 = names.at(1);const nameAtLastIndex = names.at(-1);const nameAtBeforeLastIndex = names.at(-2);const nameAtNonExistingIndex = names.at(10);console.log(nameAtIndex1); // Output : Bobconsole.log(nameAtLastIndex); // Output : Joeconsole.log(nameAtBeforeLastIndex); // Output : Aliceconsole.log(nameAtNonExistingIndex); // Output : undefined
2.concat
将给定的数组元素添加到调用者数组的末尾。
const manNames = ["Jhon", "Bob"];const womanNames = ["Alice"];const nameConcatenation = manNames.concat(womanNames);console.log(nameConcatenation); // Output : ["Jhon", "Bob", "Alice"]
3. copyWithin
将给定开始索引和结束索引之间的元素复制到目标索引。
负索引表示从最后一个开始计数（例如：-1 是最后一个元素）。
let letters = [];// Copy to index 1, all elements form the index 3 to index 5 not included ("d" and "e")letters = ["a", "b", "c", "d", "e", "f", "g", "h"];letters.copyWithin(1, 3, 5);console.log(letters);// Output : ["a", "d", "e", "d", "e", "f", "g", "h"]// Copy to index 1, all elements form the index 3 to end ("d", "e", "f", "g" and "h")letters = ["a", "b", "c", "d", "e", "f", "g", "h"];letters.copyWithin(1, 3);console.log(letters);// Output : ["a", "d", "e", "f", "g", "h", "g", "h"]// Copy to index -7 (equivalent to 2), all elements from the index -6 (equivalent to 3) to index 5 not included ("d" and "e")letters = ["a", "b", "c", "d", "e", "f", "g", "h"];letters.copyWithin(-7, -6, 5);console.log(letters);// Output : ["a", "d", "e", "d", "e", "f", "g", "h"]
4. entries
返回一个迭代器，其中，包含每个数组元素的索引/值对的数组。
const letters = ["a", "b"];const iterator1 = letters.entries();console.log(iterator1.next().value); // Output [0, 'a']console.log(iterator1.next().value); // Output : [0, 'b']console.log(iterator1.next().value); // Output : undefined
5. every
检查所有数组元素是否验证给定条件并返回 true。否则，返回 false。
const numbers = [10, 15, 20, 25, 30];const isAllNumbersBelow40 = numbers.every((number) => number < 40);console.log(isAllNumbersBelow40); // Output : trueconst isAllNumbersBelow20 = numbers.every((number) => number < 20);console.log(isAllNumbersBelow20); // Output : false
6. fill
按给定值从开始索引到结束索引填充数组。
负索引表示从最后一个开始计数（例如：-1 是最后一个元素）。
let numbers = [];/** Fill 0 on numbers start at index 1 to index 4 not included (3 elements) */numbers = [1, 1, 1, 1, 1];numbers.fill(0, 1, 4);console.log(numbers);// Output : [1, 0, 0, 0, ]/** Fill 0 on numbers start at index 1 to the end (4 elements) */numbers = [1, 1, 1, 1, 1];numbers.fill(0, 1);console.log(numbers);// Output : [1, 0, 0, 0, 0]/** Fill 0 on all numbers */numbers = [1, 1, 1, 1, 1];numbers.fill(0);console.log(numbers);// Output : [0, 0, 0, 0, 0]/** Fill 0 on numbers start at index -4 (equivalent to 2) to index -1 (equivalent to 4) not included (3 elements) */numbers = [1, 1, 1, 1, 1];numbers.fill(0, -4, -1);console.log(numbers);// Output : [1, 0, 0, 0, 1]
7.filter
返回仅包含验证条件的元素的新数组。
const names = ["Joe", "Jhon", "Alice"];const namesWith4LettersOrLess = names.filter((name) => name.length <= 4);console.log(namesWith4LettersOrLess); // Output : ["Joe", "Jhon"]
8. find
找到第一个验证条件的元素并返回它。否则，返回未定义。
const names = ["Joe", "Jhon", "Alice"];const firstNameMatchStartWithJ = names.find((name) => name.startsWith("J"));console.log(firstNameMatchStartWithJ); // Output : Joeconst firstNameMatchStartWithK = names.find((name) => name.startsWith("K"));console.log(firstNameMatchStartWithK); // Output : undefined
9. findIndex
找到第一个验证条件的元素并返回其索引。否则，返回-1。
const names = ["Joe", "Jhon", "Alice"];const firstNameMatchStartWithJ = names.findIndex((name) => name.startsWith("J"));console.log(firstNameMatchStartWithJ); // Output : 0const firstNameMatchStartWithK = names.findIndex((name) => name.startsWith("K"));console.log(firstNameMatchStartWithK); // Output : -1
10.findLast
找到验证条件的最后一个元素并将其返回。否则，返回未定义。
const names = ["Joe", "Jhon", "Alice"];const lastNameMatchStartWithJ = names.findLast((name) => name.startsWith("J"));console.log(lastNameMatchStartWithJ); // Output : Jhonconst lastNameMatchStartWithK = names.findLast((name) => name.startsWith("K"));console.log(lastNameMatchStartWithK); // Output : undefined
11. findLastIndex
找到最后一个验证条件的元素并返回其索引。否则，返回-1。
const names = ["Joe", "Jhon", "Alice"];const lastNameMatchStartWithJ = names.findLastIndex((name) => name.startsWith("J"));console.log(lastNameMatchStartWithJ); // Output : 1const lastNameMatchStartWithK = names.findLastIndex((name) => name.startsWith("K"));console.log(lastNameMatchStartWithK); // Output : -1
12. flat
在每个元素中展开任何已建立的数组，并根据给定的深度级别继续展开嵌套的数组。返回新的平面数组。
const numbers = [1, 2, [3, [4, [5, 6]]]];const flatNumbersLevel1 = numbers.flat();console.log(flatNumbersLevel1); // Output : [1, 2, 3, [4, [5, 6]]]const flatNumbersLevel2 = numbers.flat(2);console.log(flatNumbersLevel2); // Output : [1, 2, 3, 4, [5, 6]]const flatNumbers = numbers.flat(Infinity);console.log(flatNumbers); // Output : [1, 2, 3, 4, 5, 6]
13. flatMap
返回一个新数组，其中所有元素均由给定回调修改，并按 1 深度级别展平。
const users = [{name: "Jhon",votes: [3, 4]},{name: "Joe",votes: [4, 5]}];const allVotes = users.flatMap((user) => user.votes);console.log(allVotes); // Output : [3, 4, 4, 5]
14. forEach
迭代数组并对每个元素应用给定的回调。
const names = ["Joe", "Jhon", "Alice"];names.forEach((name, index, array) =>console.log(`${name} at index ${index} in the array [${array.join(", ")}]`));// Output : Joe at index 0 in the array [Joe, Jhon, Alice]// Output : Jhon at index 1 in the array [Joe, Jhon, Alice]// Output : Alice at index 2 in the array [Joe, Jhon, Alice]
15. from
从可迭代或类似数组创建数组。
/** Create an array from string */console.log(Array.from("hello"));// Output : ["h", "e", "l", "l", "o"]/** Create an array from an other array and Apply map method */console.log(Array.from([1, 2, 3], (x) => x * 2));// Output : [2, 4, 6]
16. fromAsync
从异步可迭代、可迭代或类数组创建数组。
/** Create an array from an array of async elements */const asyncArray = [new Promise((resolve) => resolve(0)),new Promise((resolve) => resolve(1))];(async () => {const array = awAIt Array.fromAsync(asyncArray);console.log(array); // Output : [0, 1]})();
17. includes
检查数组是否包含给定元素。
const letters = ["a", "b", "c"];console.log(letters.includes("b")); // Output: trueconsole.log(letters.includes("e")); // Output: false
18. indexOf
返回给定元素的第一个匹配项的索引。如果找到任何匹配项，则返回 -1。
const letters = ["a", "b", "c", "d"];/** Get index of existing letter 'b' */console.log(letters.indexOf("b")); // Output: 1/** Get index of existing letter 'b' but start searching from index 2 */console.log(letters.indexOf("b", 2)); // Output: -1/** Get index of existing letter 'b' but start searching from index -4 (equivalent to 0) */console.log(letters.indexOf("b", -4)); // Output: 1/** Get index of non existing letter 'e' */console.log(letters.indexOf("e")); // Output: -1
19. isArray
检查变量是否是数组。
const array = [];console.log(Array.isArray(array)); // Output : trueconst object = {};console.log(Array.isArray(object)); // Output : false
20. join
将所有数组元素连接到一个字符串，并用给定的分隔符将它们分开。
const letters = ["h", "e", "l", "l", "o"];/** Join all letters together with default separator comma */console.log(letters.join());// Output : h,e,l,l,o/** Join all letters together with no separator */console.log(letters.join(""));// Output : hello/** Join all letters together with dash separator */console.log(letters.join("-"));// Output : h-e-l-l-o
21. keys
返回包含索引的迭代器。
const letters = ["a", "b"];const iterator1 = letters.keys();console.log(iterator1.next().value); // Output 0console.log(iterator1.next().value); // Output : 1console.log(iterator1.next().value); // Output : undefined
22.lastIndexOf
返回给定元素的最后一个匹配项的索引。如果找到任何匹配项，则返回 -1。
const letters = ["a", "b", "b", "a"];/** Get last index of existing letter 'b' */console.log(letters.lastIndexOf("b")); // Output: 2/** Get index of non existing letter 'e' */console.log(letters.lastIndexOf("e")); // Output: -1
23. map
返回一个新数组，其中所有元素均由给定回调修改。
const numbers = [1, 2, 3];/** Double all numbers */const doubleNumebrs = numbers.map((number) => number * 2);console.log(doubleNumebrs);// Output : [2, 3, 6]/** Get number array info */const numberArrayInfo = numbers.map((element, index, array) =>`${element} at index ${index} in the array [${array.join(", ")}]`);console.log(numberArrayInfo);// Output : ["1 at index 0 in the array [1, 2, 3]", "2 at index 1 in the array [1, 2, 3]", "3 at index 2 in the array [1, 2, 3]"]
24. of
从给定的元素创建一个数组。
/** Create an array from values */const numbers = Array.of(1, 2, 3, 4);console.log(numbers);// Output: [1, 2, 3, 4]
25.pop
删除数组的最后一个元素并返回它。
/** Create an array from values */const numbers = [1, 2, 3, 4];console.log(numbers.pop()); // Output : 4console.log(numbers); // Output : [1, 2, 3]
26. push
将新元素添加到数组中。
/** add value or values to the end of array */const numbers = [1, 2, 3, 4];numbers.push(5);numbers.push(6, 7);console.log(numbers);// Output : [1, 2, 3, 4, 5, 6, 7]/** Create an array from values */
27. reduce
通过应用给定的回调将数组减少到一个值。给定的回调应在每次迭代中返回更新的值。
/** Reduce hello array to hello string */const letters = ["h", "e", "l", "l", "o"];const word = letters.reduce((accWord, letter) => `${accWord}${letter}`);console.log(word);// Output : hello
28. reduceRight
它类似于reduce方法，但从数组的最后一个元素开始迭代。
/** Reduce hello array to olleh string */const letters = ["h", "e", "l", "l", "o"];const word = letters.reduceRight((accWord, letter) => `${accWord}${letter}`);console.log(word);// Output : olleh
29. reverse
反转数组元素的顺序。
/** Reverse hello array to olleh array */const letters = ["h", "e", "l", "l", "o"];letters.reverse();console.log(letters);// Output : ["o", "l", "l", "e", "h"]
30.shift
删除数组的第一个元素并返回它。
/** Reverse number order of number array */const numbers = [1, 2, 3];numbers.reverse();console.log(numbers);// Output : [3, 2, 1];
31.slice
返回从给定开始到结束索引的子数组。
负索引表示从最后一个开始计数（例如：-1 是最后一个元素）。
const numbers = ["a", "b", "c", "d", "e"];/** Get numbers from index 1 to index 4 not included ("b", "c" and "d") */console.log(numbers.slice(1, 4));// Output : ["b", "c", "d"]/** Get numbers from index 1 to the end ("b", "c", "d" and "e") */console.log(numbers.slice(1));// Output : ["b", "c", "d", "e"]/** Get numbers from index -4 (equivalent to 1) to index -1 (equivalent to 4) not included ("b", "c" and "d") */console.log(numbers.slice(-4, -1));// Output : ["b", "c", "d"]
32. some
检查是否至少有一个元素验证给定条件。
const numbers = [10, 15, 20, 25, 30];const isAtLeastOneBelow20 = numbers.some((number) => number < 20);console.log(isAtLeastOneBelow20); // Output : trueconst isAtLeastOneBelow5 = numbers.some((number) => number < 5);console.log(isAtLeastOneBelow5); // Output : false
33. sort
通过给定的回调返回排序的数组。
如果回调返回正数，则将 a 排序在 b 之后。否则，将 b 排序在 a 之后。
let numbers = [];/** Sort number in ascendent order. Sort a after b. */numbers = [10, 100, 20, 25, 30];numbers.sort((a, b) => a - b);console.log(numbers); // Output : [10, 20, 25, 30, 100]/** Sort number in descendant order. Sort b after a */numbers = [10, 100, 20, 25, 30];numbers.sort((a, b) => b - a);console.log(numbers); // Output : [100, 30, 25, 20, 10]
34. splice
删除或替换从给定开始索引到给定结束索引的子数组。
负索引表示从最后一个开始计数（例如：-1 是最后一个元素）。
let numbers = [];/** Remove elements from index 1 to 3 elements further ([0, 0, 0]) */numbers = [1, 0, 0, 0, 1];numbers.splice(1, 3);console.log(numbers);// Output : [1, 1]/** Remove elements from index 1 to the end ([0, 0, 0, 1]) */numbers = [1, 0, 0, 0, 1];numbers.splice(1);console.log(numbers);// Output : [1]/** Remove elements from index -4 (equivalent to 1) to the end ([0, 0, 0, 1]) */numbers = [1, 0, 0, 0, 1];numbers.splice(-4);console.log(numbers);// Output : [1]/** Replace elements by 2, 2, 2 from index 1 to index 3 included ([0, 0, 0]) */numbers = [1, 0, 0, 0, 1];numbers.splice(1, 3, 2, 2, 2);console.log(numbers);// Output : [1, 2, 2, 2, 1]/** Replace elements by 2, 2, 2 from index -4 (equivalent to 1) to 3 elements further ([0, 0, 0]) */numbers = [1, 0, 0, 0, 1];numbers.splice(-4, 3, 2, 2, 2);console.log(numbers);// Output : [1, 2, 2, 2, 1]/** Add elements 2, 2, 2 at index 1 */numbers = [1, 0, 0, 0, 1];numbers.splice(1, 0, 2, 2, 2);console.log(numbers);// Output : [1, 2, 2, 2, 0, 0, 0, 1]
35. toLocaleString
将所有元素转换为语言环境字符串，将所有元素连接为字符串，同时用逗号分隔每个元素并返回字符串。
const date = [10.4, new Date("31 Aug 2022 22:00:00 UTC")];console.log(date.toLocaleString());// Output : 10.4,9/1/2022, 12:00:00 AMconsole.log(date.toLocaleString("en"));// Output : 10.4,9/1/2022, 12:00:00 AMconsole.log(date.toLocaleString("es"));// Output : 10,4,1/9/2022, 0:00:00
36. toReversed
创建一个新数组，其中，按相反顺序包含调用方数组的元素。
它类似于“reverse”方法，但它返回一个新数组而不修改调用者数组。
const numbers = [1, 2, 3];const reversedNumbers = numbers.toReversed();console.log(reversedNumbers); // Output : [3, 2, 1]console.log(numbers); // Output : [1, 2, 3]
37. toSorted
创建一个新数组，其中包含按给定回调排序的调用者数组的元素。
它类似于“sort”方法，但它返回一个新数组而不修改调用者数组。
const numbers = [10, 100, 20, 25, 30];/** Sort number in ascendent order. Sort a after b. */const numbersInAscOrder = numbers.toSorted((a, b) => a - b);console.log(numbersInAscOrder); // Output : [10, 20, 25, 30, 100]console.log(numbers); // Output : [10, 100, 20, 25, 30]/** Sort number in descendant order. Sort b after a */const numbersInDescOrder = numbers.toSorted((a, b) => b - a);console.log(numbersInDescOrder); // Output : [100, 30, 25, 20, 10]console.log(numbers); // Output : [10, 100, 20, 25, 30]
38. toSpliced
创建一个新数组，其中包含调用方数组的元素以及已替换或删除的元素。
它类似于“splice”方法，但它返回一个新数组而不修改调用者数组。
负索引表示从最后一个开始计数（例如：-1 是最后一个元素）。
let numbers = [1, 0, 0, 0, 1];/** Remove elements from index 1 to 3 elements further ([0, 0, 0]) */const splicedNumbers1 = numbers.toSpliced(1, 3);console.log(splicedNumbers1); // Output : [1, 1]console.log(numbers); // Output : [1, 0, 0, 0, 1]/** Replace elements by 2, 2, 2 from index 1 to index 3 included ([0, 0, 0]) */const splicedNumbers2 = numbers.toSpliced(1, 3, 2, 2, 2);console.log(splicedNumbers2); // Output : [1, 2, 2, 2, 1]console.log(numbers); // Output : [1, 0, 0, 0, 1]/** Add elements 2, 2, 2 at index 1 */const splicedNumbers3 = numbers.toSpliced(1, 0, 2, 2, 2);console.log(splicedNumbers3); // Output : [1, 2, 2, 2, 0, 0, 0, 1]console.log(numbers); // Output : [1, 0, 0, 0, 1]
39. toString
通过将所有元素连接到字符串，同时用逗号分隔每个元素并返回字符串，将所有元素转换为区域设置字符串。
const letters = ["a", "b", "c", "d"];/** Join all letters together with default separator comma */console.log(letters.toString());// Ouput : a,b,c,d
40. unshift
将元素添加到数组中第一个元素之前。
const numbers = [3, 4];numbers.unshift(0, 1, 2);console.log(numbers); // Output : [0, 1, 2, 3, 4]
41. values
返回一个迭代器，该迭代器迭代数组中每个项目的值。
const letters = ["a", "b"];const letterIterator = letters.values();console.log(letterIterator.next().value); // Output : aconsole.log(letterIterator.next().value); // Output : bconsole.log(letterIterator.next().value); // Output : undefined
42. with
创建一个新数组，其中包含调用方数组的元素以及给定索引处替换的给定值。
负索引表示从最后一个开始计数（例如：-1 是最后一个元素）。
const letters = ["a", "k", "c", "d"];/** replace k at index 1 with b */console.log(letters.with(1, "b"));// Output : ["a", "b", "c", "d"]/** replace k at index -3 (equivalent to 1) with b */console.log(letters.with(-3, "b"));// Output : ["a", "b", "c", "d"]
结论
以上就是42个数组的全部方法的分享，希望这期内容对你有所帮助。
另外，就是我们在编写任何处理数组的代码之前，请考虑可重用性并检查是否已经存在可以使用的现有方法。
我自己最常用的数组方法是：filter、map、reduce、some 和 every。
如果你也有自己最常用的数组方法，欢迎在留言区给我们大家一起来分享。
