归并方法

    1. const arr = [1, 2, 3, 4, 5];
    2. /**
    3.  * reduce/reduceRight
    4.  * v1: 归并函数
    5.  *    v1: 归并值
    6.  *    v2: 当前项
    7.  *    v3: 当前项索引
    8.  *    v4: 数组本身
    9.  * v2: 归并起点
    10.  */
    11. const red = arr.reduce(function (x, y, i, arr) {
    12.   console.log("i :>> ", i);
    13.   return x * y;
    14. });
    15. console.log(red);
    16. const redR = arr.reduceRight((x, y, i, arr) => x * y);
    17. console.log(redR);

    案例: 将班级中同学的名字全部提取出来

    1. const classes = [
    2.   {
    3.     class: "一班",
    4.     students: [
    5.       {
    6.         name: "小王",
    7.         age: 18,
    8.       },
    9.       {
    10.         name: "小李",
    11.         age: 21,
    12.       },
    13.     ],
    14.   },
    15.   {
    16.     class: "二班",
    17.     students: [
    18.       {
    19.         name: "小孙",
    20.         age: 16,
    21.       },
    22.       {
    23.         name: "小赵",
    24.         age: 28,
    25.       },
    26.     ],
    27.   },
    28. ];
    30. const studentsName = classes.reduce(function (pre, cur, index, array) {
    31.   let stus = pre.students.reduce(function (pre, cur, index, array) {
    32.     return pre.name.concat(cur.name);
    33.   });
    34.   return stus.concat(
    35.     cur.students.reduce(function (pre, cur, index, array) {
    36.       return pre.name.concat(cur.name);
    37.     })
    38.   );
    39. });
    40. console.log(studentsName);

    案例: 统计

    1. const fruits = ["苹果", "橘子", "梨", "苹果"];
    2. const fruitsCount = fruits.reduce(function (pre, next) {
    3.   pre[next] = pre[next] + 1 || 1;
    4.   return pre;
    5. }, {});
    6. console.log(fruitsCount);

    案例: 去重

    1. const fruitsOnly = fruits.reduce(function (pre, cur, index, array) {
    2.   if (pre.indexOf(cur) == -1) {
    3.     pre.push(cur);
    4.   }
    5.   return pre;
    6. }, []);
    7. console.log(fruitsOnly);