Question

我一直试图找到一种方法来正确定义数组作为构造函数值之一。假设我们有一个学生，我们需要有一个成绩阵列，然后使用我们需要的阵列来获得学生成绩的平均分。可悲的是，我只发现了一些用其他编程语言解决这个问题的线程。这是我认为可行的：

function student(name, surname, number, grades) {
this.name = name;
this.surname = surname;
this.number = number;
this.grades = [];
this.average = function(grades) {
 var sum = 0;
 for(var i = 0; i < grades.length; i++) {
  sum + = grades[i];}
  var average = sum / grades.length;
  return average;
 }
}

然后

var student1 = new student("Peter","Cat",14444,[2,3,4]);
console.log(student1);

不幸的是，它显示我的成绩数组为空白，我无法查看我的平均功能是否正常工作。我应该更改哪些部分，以便在grade数组中实际有一些值？

谢谢。

Answer 1

您可以通过使用ES6解决相同的问题，在您的代码中，您正在使用函数内部的空数组初始化this.grade=[]，因此仅对空数组进行平均值的进一步处理。为了良好作法，应为函数参数分配一个默认值，这样，如果我们错误地不将数组作为参数传递，则函数参数将使用默认值。附加代码段，以便在ES6中轻松理解。

class std{
constructor(name, surname, number, grades = []) {
    this.name = name;
    this.surname = surname;
    this.number = number;
    this.grades = grades;
}  

average() {
  if(this.grades.length !== 0){
    return this.grades.reduce((previous, current) => previous + current, 0) / 
    this.grades.length
  } else { return "no grades mentioned"; }
 }
}

var student1 = new std("Peter", "Cat", 14444, [1, 3, 4]);
console.log("Average: ", student1.average());
//add new student
var student2 = new std("Prasanna", "sasne", 14444);
console.log(student2); 

//student2.grades.push(7)
//console.log("New Average: ", student2.average() )

Answer 2

你有几件事搞砸了。如果您要将等级数组作为参数传递，那么您需要使用以下内容设置成绩：

this.grades = grades;

同样在平均功能中，你需要引用this.grades成绩而不仅仅是成绩。这将允许您稍后添加更多成绩并仍然获得正确的平均值。您还可以考虑通过使用以下内容定义构造函数来使成绩可选：

function student(name, surname, number, grades =[])

然后，如果你没有传入一个值，那么一个空数组将等着你。

最后你可能会有：

＆＃13;

function student(name, surname, number, grades = []) {
  this.name = name;
  this.surname = surname;
  this.number = number;
  this.grades = grades;
  this.average = function() {
    return this.grades.reduce((a, c) => a + c, 0) / this.grades.length
  }
}

var student1 = new student("Peter", "Cat", 14444, [2, 3, 4]);
console.log("Average: ", student1.average())

// add another grade:
student1.grades.push(6)
console.log("New Average: ", student1.average() )

＆＃13;

Answer 3

您已将grades传递到student()函数，因此您无需将其传递给student.average函数（因为内部函数将会已经可以访问外部函数参数）。因此，您也不需要设置this.grades = []。

此外，sum + = grades[i]应为sum += grades[i]。

简单地修复此错误，然后省略将grades传递到内部函数中将正确显示平均值，如下所示：

＆＃13;

function student(name, surname, number, grades) {
  this.name = name;
  this.surname = surname;
  this.number = number;
  this.average = function() {
    var sum = 0;
    for (var i = 0; i < grades.length; i++) {
      sum += grades[i];
    }
    var average = sum / grades.length;
    return average;
  }
}

var student1 = new student("Peter", "Cat", 14444, [2, 3, 4]);
console.log(student1.average());

＆＃13;

Answer 4

您对变量的初始化是一个空数组。

this.grades = [];

应该是

this.grades = grades;

但是，我建议你学习一些javascript ES6 / ECMAScript 2015并使用类。 this source

class Student {
  constructor(grades) {
    //... Other code
    this.grades = grades;
  }
}

Answer 5

你可以使用这一行：

<块引用>

function student(name, surname, number, grades){ }

而不是这个：

<块引用>

function student(name, surname, number, grades = [ ]){ }

function student(name, surname, number, grades) {
  this.name = name;
  this.surname = surname;
  this.number = number;
  this.grades = grades;
  this.average = function() {
    return this.grades.reduce((a, c) => a + c, 0) / this.grades.length
  }
}

var student1 = new student("Peter", "Cat", 14444, [2, 3, 4]);
console.log("Average: ", student1.average())

// add another grade:
student1.grades.push(6)
console.log("New Average: ", student1.average() )

Answer 6

我们可以使用对象方法来存储平均值：

function Student(name, surname, number, grades = [])
{
    this.name = name;
    this.surname = surname;
    this.number = number;
    this.grades = grades;

    //Method to calculate the Average
    this.average = function()
    {
        if(this.grades.length !==0)
        {
            //Return the Average Calculation
            return this.grades.reduce((previous, current) => previous + current, 0) / this.grades.length
        }
        else
        {
            //This will return if grades not provided
            return "No Grades Mentioned"
        }
    }

}

//With Grades
var student1 = new Student("Srinivasan", "Raja", 1635, [22,43,67,89,90]);
console.log(student1, "Average: "+ student1.average());

//Without Grades
var student1 = new Student("Denny", "Lawrence", 1635);
console.log(student1, "Average: "+ student1.average());

使用Javascript在构造函数中使用数组

6 个答案: