更新JavaScript ForEach中的迭代数组

Question

  

替换年龄较大的员工＆gt;与年轻员工50岁。

我正在尝试更新我forEach()数组中的项目。分配current失败，同时注意index并在forEach()阻止工作后替换项目。请解释一下这种行为？

var youngerEmployee = {
  name: {
    first: 'B',
    last: 'C'
  },
  age: 25
}

var employees = [
  {
    name: {
      first: 'X',
      last: 'Y'
    },
    age: 45
  },
  {
    name: {
      first: 'A',
      last: 'B'
    },
    age: 54
  }
];

/* --- Failed approach --- */

employees.forEach(

  (employee) => {

    if(employee.age > 50) {

      employee = youngerEmployee;

    }

  }

);

console.log(employees);

/* --- Successful approach --- */

var i = -1;

employees.forEach(

  (employee, index) => {

    if(employee.age > 50) {

      i = index;

    }

  }

);

employees[i] = youngerEmployee;

console.log(employees);

JSBin

Answer 1

在“失败的方法”中，employees数组未更改，因为employee引用了数组中的当前员工。通过分配employee = youngerEmployee，您可以更改引用，否则employees数组不会受到影响。

Answer 2

使用map代替forEach它不会操纵原始数组

var youngerEmployee = {
  name: {
    first: 'B',
    last: 'C'
  },
  age: 25
}

var employees = [{
    name: {
      first: 'X',
      last: 'Y'
    },
    age: 45
  },
  {
    name: {
      first: 'A',
      last: 'B'
    },
    age: 54
  }
];
var x = employees.map(function(item) {
  if (item.age > 50) {
    item = youngerEmployee
  }
  return item

});
console.log(x)

Answer 3

当您需要修改某些数组项时，可以使用数组map()代替forEach()：

＆＃13;

＆＃13;

var youngerEmployee = {
  name: {
    first: 'B',
    last: 'C'
  },
  age: 25
}

var employees = [
  {
    name: {
      first: 'X',
      last: 'Y'
    },
    age: 45
  },
  {
    name: {
      first: 'A',
      last: 'B'
    },
    age: 54
  }
];

employees = employees.map(
  (employee) => {
    if(employee.age > 50) {
      employee = youngerEmployee;
    }
    return employee;
  }
);

console.log(employees);

＆＃13;

＆＃13;

＆＃13;