JavaScript: Getting undefined value

Question

I have written a function that takes an array of objects( students3 ) and prints the name of the student and their average test score.

 var students3 = [ { name : "Anthony", id : 0, grades : [{ id : 0, score : 84},{ id : 1, score : 20},{ id : 2, score : 80}] }, { name : "Winnie", id : 1, grades : [{ id : 0, score : 62},{ id : 1, score : 56},{ id : 2, score : 100}] }, { name : "Pawandeep", id : 2, grades : [{ id : 0, score : 79},{ id : 1, score : 92},{ id : 2, score : 49}] } ]; 

My solution:

 function getAverageScore(student) { var sum = 0; var grades = student.grades; for(var i = 0; i < grades.length; i++) { var grade = grades[i]; sum += grade.score; } var avg = sum/grades.length; return avg; } function printAverageGrade(students) { for(var i = 0; i < students.length; i++) { var student = students[i]; var averageScore = getAverageScore(student); console.log(student.name, averageScore); } } 

Expected result after running console.log(printAverageGrade(students3)); is:

Anthony 61.333333333333336

Winnie 72.66666666666666

Pawandeep 73.33333333333333

My result:

Anthony 61.333333333333336

Winnie 72.66666666666666

Pawandeep 73.33333333333333

undefined

Anyone can tell me why I am getting an undefined value in my result? Thank you.

Answer 1

The printAverageGrade function itself itself logs messages to the console. It doesn't have a return statement, so it returns undefined .

If you log printAverageGrade(students3) to the console, you will log undefined .

Solution: don't log printAverageGrade(students3) :

console.log(printAverageGrade(students3)) → printAverageGrade(students3)

Answer 2

That last line is the return value of the function. If you look at the getAverageScore(student) function, you can see that you return avg; , which is what gives that value.

printAverageGrades doesn't return anything, so its return value is undefined . The console logging works though, so as long as you don't try to use it to set any variables, this code is fine.

Answer 3

If you are running from your browser's JavaScript console, are you sure you're not seeing the return value of printAverageGrade ? See this simple example:

> function foo() { console.log("hello"); }
<- undefined
> foo()
  hello
<- undefined

The two undefined are from the console trying to print the return value of the immediate command, and if we try this instead:

> function foo() { console.log("hello"); return "defined"; }
<- undefined
> foo()
  hello
<- "defined"

---

Specifically, your sample code uses:

console.log(printAverageGrade(students3));

Since printAverageGrade() returns nothing, the console logs undefined .