爲什麼我的變量未定義

我有這個功能爲什麼我的變量未定義

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"};  
      }

然後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>";

然而，當我嘗試去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該函數並將其分配給一個變量來定義它了？

來源

2017-02-28 Alicat

你忘記返回數組 –

其他人說什麼。另外，函數中的'var students = []'對外部世界沒有影響。該var僅存在於該函數中。 –

更改此代碼的功能。問題是你沒有返回變量學生，當你超出了變量不存在的範圍時。隨着返回，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;    
}

來源

2017-02-28 11:09:30 acostela

請不要發佈不完整的答案，然後編輯它們以使它們完整。首先發佈一個完整的答案。 –

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; 
}

來源

2017-02-28 11:09:46

您需要在該變量的函數的最後返回學生陣列從getStudents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();它只是做一個函數調用，而不是分配數組。

來源

2017-02-28 11:11:28 DibsyJr

-1

您不能請求在創建對象的函數調用中沒有返回的對象的長度。由於getStudents（）函數沒有返回值或對象，因此您得到的錯誤，因此您沒有爲學生變量賦值。上的jsfiddle

使用開發者控制檯下面來看看這個證明

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);

來源

2017-02-28 11:15:00

爲什麼我的變量未定義

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