数组在编程中扮演着重要的角色，它们允许我们存储和操作一系列的元素。以下是对数组操作方法的全面介绍：
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Array.concat()
concat()方法用于合并两个或多个数组。此方法不会更改现有数组，而是返回一个新数组。const array1 = ['a', 'b', 'c']; const array2 = ['d', 'e', 'f']; const array3 = array1.concat(array2); console.log(array3);
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Array.copyWithin()
copyWithin()方法浅复制数组的一部分到同一数组中的另一个位置，并返回它，不会改变原数组的长度。const array1 = ['a', 'b', 'c', 'd', 'e']; // Copy to index 0 the element at index 3 console.log(array1.copyWithin(0, 3, 4)); // Expected output: Array ["d", "b", "c", "d", "e"] // Copy to index 1 all elements from index 3 to the end console.log(array1.copyWithin(1, 3)); // Expected output: Array ["d", "d", "e", "d", "e"]
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Array.entries()
entries()方法返回一个新的数组迭代器对象，该对象包含数组中每个索引的键/值对。const array1 = ['a', 'b', 'c']; const iterator1 = array1.entries(); console.log(iterator1.next().value); // Expected output: Array [0, "a"] console.log(iterator1.next().value); // Expected output: Array [1, "b"]
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Array.every()
every()方法测试一个数组内的所有元素是否都能通过指定函数的测试。它返回一个布尔值。const isBelowThreshold = (currentValue) => currentValue < 40; const array1 = [1, 30, 39, 29, 10, 13]; console.log(array1.every(isBelowThreshold)); // Expected output: true
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Array.fill()
fill()方法用一个固定值填充一个数组中从起始索引（默认为0）到终止索引（默认为array.length）内的全部元素。它返回修改后的数组。const array1 = [1, 2, 3, 4]; // Fill with 0 from position 2 until position 4 console.log(array1.fill(0, 2, 4)); // Expected output: Array [1, 2, 0, 0] // Fill with 5 from position 1 console.log(array1.fill(5, 1)); // Expected output: Array [1, 5, 5, 5] console.log(array1.fill(6)); // Expected output: Array [6, 6, 6, 6]
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Array.filter()
filter()方法创建给定数组一部分的浅拷贝，其包含通过所提供函数实现的测试的所有元素。const words = ['spray', 'elite', 'exuberant', 'destruction', 'present']; const result = words.filter((word) => word.length > 6); console.log(result); // Expected output: Array ["exuberant", "destruction", "present"]
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Array.find()
find()方法返回数组中满足提供的测试函数的第一个元素的值。否则返回 undefined。const array1 = [5, 12, 8, 130, 44]; const found = array1.find((element) => element > 10); console.log(found); // Expected output: 12
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Array.findIndex()
findIndex()方法返回数组中满足提供的测试函数的第一个元素的索引。若没有找到对应元素则返回 -1。const array1 = [5, 12, 8, 130, 44]; const isLargeNumber = (element) => element > 13; console.log(array1.findIndex(isLargeNumber));
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Array.flat()
flat()方法创建一个新的数组，并根据指定深度递归地将所有子数组元素拼接到新的数组中。const arr1 = [0, 1, 2, [3, 4]]; console.log(arr1.flat()); // expected output: Array [0, 1, 2, 3, 4] const arr2 = [0, 1, [2, [3, [4, 5]]]]; console.log(arr2.flat()); // expected output: Array [0, 1, 2, Array [3, Array [4, 5]]] console.log(arr2.flat(2)); // expected output: Array [0, 1, 2, 3, Array [4, 5]] console.log(arr2.flat(Infinity)); // expected output: Array [0, 1, 2, 3, 4, 5]
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Array.flatMap()
flatMap()方法对数组中的每个元素应用给定的回调函数，然后将结果展开一级，返回一个新数组。const arr1 = [1, 2, 1]; const result = arr1.flatMap((num) => (num === 2 ? [2, 2] : 1)); console.log(result); // Expected output: Array [1, 2, 2, 1]
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Array.forEach()
forEach()方法对数组的每个元素执行一次给定的函数。const array1 = ['a', 'b', 'c']; array1.forEach((element) => console.log(element));
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Array.includes()
includes()方法用来判断一个数组是否包含一个指定的值，根据情况，如果包含则返回true，否则返回false。
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const array1 = [1, 2, 3]; console.log(array1.includes(2)); // Expected output: true const pets = ['cat', 'dog', 'bat']; console.log(pets.includes('cat')); // Expected output: true console.log(pets.includes('at')); // Expected output: falseArray.indexOf()
indexOf()方法返回数组中第一次出现给定元素的下标，如果不存在则返回 -1。const beasts = ['ant', 'bison', 'camel', 'duck', 'bison']; console.log(beasts.indexOf('bison')); // Expected output: 1 // Start from index 2 console.log(beasts.indexOf('bison', 2)); // Expected output: 4 console.log(beasts.indexOf('giraffe')); // Expected output: -1
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Array.join()
join()方法将一个数组的所有元素连接成一个字符串并返回这个字符串，用逗号或指定的分隔符字符串分隔。如果数组只有一个元素，那么将返回该元素而不使用分隔符。const elements = ['Fire', 'Air', 'Water']; console.log(elements.join()); // Expected output: "Fire,Air,Water" console.log(elements.join('')); // Expected output: "FireAirWater" console.log(elements.join('-')); // Expected output: "Fire-Air-Water"
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Array.keys()
keys()方法返回一个新的数组迭代器对象，其中包含数组中每个索引的键。for (const key of iterator) { console.log(key); } // Expected output: 0 // Expected output: 1 // Expected output: 2
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Array.lastIndexOf()
lastIndexOf()方法返回数组中给定元素最后一次出现的索引，如果不存在则返回 -1。该方法从fromIndex开始向前搜索数组。const animals = ['Dodo', 'Tiger', 'Penguin', 'Dodo']; console.log(animals.lastIndexOf('Dodo')); // Expected output: 3 console.log(animals.lastIndexOf('Tiger')); // Expected output: 1
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Array.map()
map()方法创建一个新数组，这个新数组由原数组中的每个元素都调用一次提供的函数后的返回值组成。const array1 = [1, 4, 9, 16]; // Pass a function to map const map1 = array1.map((x) => x * 2); console.log(map1); // Expected output: Array [2, 8, 18, 32]
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Array.pop()
pop()方法从数组中删除最后一个元素，并返回该元素的值。此方法会更改数组的长度。const plants = ['broccoli', 'cauliflower', 'cabbage', 'kale', 'tomato']; console.log(plants.pop()); // Expected output: "tomato" console.log(plants); // Expected output: Array ["broccoli", "cauliflower", "cabbage", "kale"] plants.pop(); console.log(plants); // Expected output: Array ["broccoli", "cauliflower", "cabbage"]
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Array.push()
push()方法将指定的元素添加到数组的末尾，并返回新的数组长度。const animals = ['pigs', 'goats', 'sheep']; const count = animals.push('cows'); console.log(count); // Expected output: 4 console.log(animals); // Expected output: Array ["pigs", "goats", "sheep", "cows"] animals.push('chickens', 'cats', 'dogs'); console.log(animals); // Expected output: Array ["pigs", "goats", "sheep", "cows", "chickens", "cats", "dogs"]
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Array.reduce()
reduce()方法对数组中的每个元素按序执行一个提供的 reducer 函数，每一次运行 reducer 会将先前元素的计算结果作为参数传入，最后将其结果汇总为单个返回值。- 第一次执行回调函数时，不存在“上一次的计算结果”。如果需要回调函数从数组索引为 0 的元素开始执行，则需要传递初始值。否则，数组索引为 0 的元素将被用作初始值，迭代器将从第二个元素开始执行（即从索引为 1 而不是 0 的位置开始）。
const array1 = [1, 2, 3, 4]; // 0 + 1 + 2 + 3 + 4 const initialValue = 0; const sumWithInitial = array1.reduce( (accumulator, currentValue) => accumulator + currentValue, initialValue, ); console.log(sumWithInitial); // Expected output: 10
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Array.reduceRight()
reduceRight()方法对累加器（accumulator）和数组的每个值（按从右到左的顺序）应用一个函数，并使其成为单个值。const array1 = [ [0, 1], [2, 3], [4, 5], ]; const result = array1.reduceRight((accumulator, currentValue) => accumulator.concat(currentValue), ); console.log(result); // Expected output: Array [4, 5, 2, 3, 0, 1]
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Array.reverse()
reverse()方法就地反转数组中的元素，并返回同一数组的引用。数组的第一个元素会变成最后一个，数组的最后一个元素变成第一个。换句话说，数组中的元素顺序将被翻转，变为与之前相反的方向。const array1 = ['one', 'two', 'three']; console.log('array1:', array1); // Expected output: "array1:" Array ["one", "two", "three"] const reversed = array1.reverse(); console.log('reversed:', reversed); // Expected output: "reversed:" Array ["three", "two", "one"] // Careful: reverse is destructive -- it changes the original array. console.log('array1:', array1); // Expected output: "array1:" Array ["three", "two", "one"]
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Array.shift()
shift()方法从数组中删除第一个元素，并返回该元素的值。此方法更改数组的长度。const array1 = [1, 2, 3]; const firstElement = array1.shift(); console.log(array1); // Expected output: Array [2, 3] console.log(firstElement); // Expected output: 1
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Array.slice()
slice()方法返回一个新的数组对象，这一对象是一个由start和end决定的原数组的浅拷贝（包括start，不包括end），其中start和end代表了数组元素的索引。原始数组不会被改变。const animals = ['ant', 'bison', 'camel', 'duck', 'elephant']; console.log(animals.slice(2)); // Expected output: Array ["camel", "duck", "elephant"] console.log(animals.slice(2, 4)); // Expected output: Array ["camel", "duck"] console.log(animals.slice(1, 5)); // Expected output: Array ["bison", "camel", "duck", "elephant"] console.log(animals.slice(-2)); // Expected output: Array ["duck", "elephant"] console.log(animals.slice(2, -1)); // Expected output: Array ["camel", "duck"] console.log(animals.slice()); // Expected output: Array ["ant", "bison", "camel", "duck", "elephant"]
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Array.some()
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const array = [1, 2, 3, 4, 5]; // Checks whether an element is even const even = (element) => element % 2 === 0; console.log(array.some(even)); // Expected output: true
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Array.sort()
sort()方法就地对数组的元素进行排序，并返回对相同数组的引用。默认排序是将元素转换为字符串，然后按照它们的 UTF-16 码元值升序排序。- 由于它取决于具体实现，因此无法保证排序的时间和空间复杂度。
const months = ['March', 'Jan', 'Feb', 'Dec']; months.sort(); console.log(months); // Expected output: Array ["Dec", "Feb", "Jan", "March"] const array1 = [1, 30, 4, 21, 100000]; array1.sort(); console.log(array1); // Expected output: Array [1, 100000, 21, 30, 4]
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Array.splice()
splice()方法就地移除或者替换已存在的元素和/或添加新的元素。const months = ['Jan', 'March', 'April', 'June']; months.splice(1, 0, 'Feb'); // Inserts at index 1 console.log(months); // Expected output: Array ["Jan", "Feb", "March", "April", "June"] months.splice(4, 1, 'May'); // Replaces 1 element at index 4 console.log(months); // Expected output: Array ["Jan", "Feb", "March", "April", "May"]
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Array.toLocaleString()
toLocaleString()方法返回一个字符串，表示数组中的所有元素。每个元素通过调用它们自己的toLocaleString方法转换为字符串，并且使用特定于语言环境的字符串（例如逗号“,”）分隔开。const array1 = [1, 'a', new Date('21 Dec 1997 14:12:00 UTC')]; const localeString = array1.toLocaleString('en', { timeZone: 'UTC' }); console.log(localeString); // Expected output: "1,a,12/21/1997, 2:12:00 PM", // This assumes "en" locale and UTC timezone - your results may vary
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Array.toString()
toString()方法返回一个字符串，表示指定的数组及其元素。const array1 = [1, 2, 'a', '1a']; console.log(array1.toString()); // Expected output: "1,2,a,1a"
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Array.unshift()
unshift()方法将指定元素添加到数组的开头，并返回数组的新长度。const array1 = [1, 2, 3]; console.log(array1.unshift(4, 5)); // Expected output: 5 console.log(array1); // Expected output: Array [4, 5, 1, 2, 3]
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Array.values()
values()方法返回一个新的数组迭代器对象，该对象迭代数组中每个元素的值。const array1 = ['a', 'b', 'c']; const iterator = array1.values(); for (const value of iterator) { console.log(value); } // Expected output: "a" // Expected output: "b" // Expected output: "c"