很多时候，我们在操作数组的时候往往就是一个for循环干到底，对数组提供的其它方法视而不见。看完本文，希望你可以换种思路处理数组，然后可以写出更加漂亮、简洁、函数式的代码。
reduce 数组里所有值的和 var sum = [0, 1, 2, 3].reduce(function (a, b) { return a + b; }, 0); // sum is 6 将二维数组转化为一维数组 var flattened = [[0, 1], [2, 3], [4, 5]].reduce( function (a, b) { return a.concat(b); }, [] ); // flattened is [0, 1, 2, 3, 4, 5] 计算数组中每个元素出现的次数 var names = ['Alice', 'Bob', 'Tiff', 'Bruce', 'Alice']; var countedNames = names.reduce(function (allNames, name) { if (name in allNames) { allNames[name]++; } else { allNames[name] = 1; } return allNames; }, {}); // countedNames is: // { 'Alice': 2, 'Bob': 1, 'Tiff': 1, 'Bruce': 1 } 使用扩展运算符和initialValue绑定包含在对象数组中的数组 // friends - an array of objects // where object field "books" - list of favorite books var friends = [{ name: 'Anna', books: ['Bible', 'Harry Potter'], age: 21 }, { name: 'Bob', books: ['War and peace', 'Romeo and Juliet'], age: 26 }, { name: 'Alice', books: ['The Lord of the Rings', 'The Shining'], age: 18 }]; // allbooks - list which will contain all friends' books + // additional list contained in initialValue var allbooks = friends.reduce(function (prev, curr) { return [...prev, ...curr.books]; }, ['Alphabet']); // allbooks = [ // 'Alphabet', 'Bible', 'Harry Potter', 'War and peace', // 'Romeo and Juliet', 'The Lord of the Rings', // 'The Shining' // ] 数组去重 var arr = [1, 2, 1, 2, 3, 5, 4, 5, 3, 4, 4, 4, 4]; var result = arr.sort().reduce( function (init, current) { if (init.length === 0 || init[init.length - 1] !== current) { init.push(current); } return init; }, [] ); console.log(result); //[1,2,3,4,5] 数组变整数 var arr = [1, 3, 5, 7, 9]; arr.reduce(function (x, y) { return x * 10 + y; }); // 13579 map 求数组中每个元素的平方根 var numbers = [1, 4, 9]; var roots = numbers.map(Math.sqrt); // roots的值为[1, 2, 3], numbers的值仍为[1, 4, 9] 格式化数组中的对象 var kvArray = [{key: 1, value: 10}, {key: 2, value: 20}, {key: 3, value: 30}]; var reformattedArray = kvArray.map(function (obj) { var rObj = {}; rObj[obj.key] = obj.value; return rObj; }); // reformattedArray 数组为： [{1: 10}, {2: 20}, {3: 30}], // kvArray 数组未被修改: // [{key: 1, value: 10}, // {key: 2, value: 20}, // {key: 3, value: 30}] 用一个仅有一个参数的函数来mapping一个数字数组 var numbers = [1, 4, 9]; var doubles = numbers.map(function(num) { return num * 2; }); // doubles数组的值为： [2, 8, 18] // numbers数组未被修改： [1, 4, 9] 反转字符串 var str = '12345'; Array.prototype.map.call(str, function(x) { return x; }).reverse().join(''); // 输出: '54321' // Bonus: use '===' to test if original string was a palindrome every 检测所有数组元素的大小 function isBigEnough(element, index, array) { return (element >= 10); } var passed = [12, 5, 8, 130, 44].every(isBigEnough); // passed is false passed = [12, 54, 18, 130, 44].every(isBigEnough); // passed is true filter 筛选排除掉所有的小值 function isBigEnough(element) { return element >= 10; } var filtered = [12, 5, 8, 130, 44].filter(isBigEnough); // filtered is [12, 130, 44] find 用对象的属性查找数组里的对象 var inventory = [ {name: 'apples', quantity: 2}, {name: 'bananas', quantity: 0}, {name: 'cherries', quantity: 5} ]; function findCherries(fruit) { return fruit.name === 'cherries'; } console.log(inventory.find(findCherries)); // { name: 'cherries', quantity: 5 } 寻找数组中的质数 function isPrime(element, index, array) { var start = 2; while (start <= Math.sqrt(element)) { if (element % start++ < 1) { return false; } } return element > 1; } console.log([4, 6, 8, 12].find(isPrime)); // undefined, not found console.log([4, 5, 8, 12].find(isPrime)); // 5 some 测试数组元素的值 function isBigEnough(element, index, array) { return (element >= 10); } var passed = [2, 5, 8, 1, 4].some(isBigEnough); // passed is false passed = [12, 5, 8, 1, 4].some(isBigEnough); // passed is true sort 升序排序 var list = [1, 3, 7, 6]; list.sort(function(a, b) { return a-b; }); 降序排序 var list = [1, 3, 7, 6]; list.sort(function(a, b) { return b-a; }); 使用映射改善排序 // 需要被排序的数组 var list = ['Delta', 'alpha', 'CHARLIE', 'bravo']; // 对需要排序的数字和位置的临时存储 var mapped = list.map(function (el, i) { return {index: i, value: el.toLowerCase()}; }) // 按照多个值排序数组 mapped.sort(function (a, b) { return +(a.value > b.value) || +(a.value === b.value) - 1; }); // 根据索引得到排序的结果 var result = mapped.map(function (el) { return list[el.index]; });