為什么我的變量未定義

Question

我有這個功能

    function getStudents() {
                    var students = [];
                    students[0] = {name: "Anna", mark: 65, sex: "female"};
                    students[1] = {name: "James", mark:33, sex: "male"};
                    students[2] = {name: "William", mark: 87, sex: "male"};
                    students[3] = {name: "Jane", mark: 72, sex: "female"};
                    students[4] = {name: "Rikki", mark: 60, sex: "male"};
                    students[5] = {name: "Angela", mark: 58, sex: "female"};    
            }

然后在身體我嘗試這樣做：

        var students = getStudents();

        var referrals = ["James", "Angela"];
                for(var i = 0; i < students.length; i++){
        var pTag ="<p>";

但是，一旦我嘗試通過循環，它告訴我它不能做一個未定義變量的.length，但我想我已經通過調用函數並將其賦值給變量來定義它？

Answer 1

更改此代碼的功能。 問題是你沒有返回變量學生，當你超出范圍時，變量不再存在。 返回時，您將在調用函數時將其分配給變量。

function getStudents() {
                var students = [];
                students[0] = {name: "Anna", mark: 65, sex: "female"};
                students[1] = {name: "James", mark:33, sex: "male"};
                students[2] = {name: "William", mark: 87, sex: "male"};
                students[3] = {name: "Jane", mark: 72, sex: "female"};
                students[4] = {name: "Rikki", mark: 60, sex: "male"};
                students[5] = {name: "Angela", mark: 58, sex: "female"};    
                return students;            
}

Answer 2

你應該return變量

function getStudents() {
    var students = [];
    students[0] = {name: "Anna", mark: 65, sex: "female"};
    students[1] = {name: "James", mark:33, sex: "male"};
    students[2] = {name: "William", mark: 87, sex: "male"};
    students[3] = {name: "Jane", mark: 72, sex: "female"};
    students[4] = {name: "Rikki", mark: 60, sex: "male"};
    students[5] = {name: "Angela", mark: 58, sex: "female"};    
    return students;
}

Answer 3

您需要在函數末尾返回students數組，以便從getStudents為變量分配數組：

function getStudents() {
     var students = [];
     students[0] = {name: "Anna", mark: 65, sex: "female"};
     students[1] = {name: "James", mark:33, sex: "male"};
     students[2] = {name: "William", mark: 87, sex: "male"};
     students[3] = {name: "Jane", mark: 72, sex: "female"};
     students[4] = {name: "Rikki", mark: 60, sex: "male"};
     students[5] = {name: "Angela", mark: 58, sex: "female"}; 
     return students;   
}

否則你說var students = getStudents(); 它只是在進行函數調用而不是分配數組。

Answer 4

您不能在創建對象的函數調用中請求未返回的對象的長度。 您沒有為學生變量分配任何內容，因為getStudents（）函數不會返回值或對象，從而導致您獲得錯誤。

在下面的jsfiddle上使用開發者控制台來查看此演示

的jsfiddle

function getStudents() {
    var students = [];
  students[0] = {name: "Anna", mark: 65, sex: "female"};
  students[1] = {name: "James", mark:33, sex: "male"};
  students[2] = {name: "William", mark: 87, sex: "male"};
  students[3] = {name: "Jane", mark: 72, sex: "female"};
  students[4] = {name: "Rikki", mark: 60, sex: "male"};
  students[5] = {name: "Angela", mark: 58, sex: "female"};  

  return students;
}

var students = getStudents();
//var referrals = ["James", "Angela"];
console.log(students);