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JavaScript Introducing ES2015 ES2015 Basics Let and Const

Posted by Johnny Garces
Johnny Garces
Courses Plus Student 8,551 Points

Let variables and block scope

I have an example code that has two let variables- one on the outer function scope, and one inside a block-scope within the if-statement.

Why does createStudent('Ken') print "James"? Shouldn't it print "Ken"? 

(function (){
    let student = {name: 'James'};
    function createStudent(name){
        if(true){
         let student = {name: name};
        }
        return student;
    }
    console.log(createStudent('Ken'));
    console.log(student);
})();
Tray Denney
Tray Denney
Courses Plus Student 12,884 Points
Tray Denney
Tray Denney
Courses Plus Student 12,884 Points

In that case it is because you are returning the wrong student. Try:

(function (){
    let student = {name: 'James'};
    function createStudent(name){
        if(true){
         let student = {name: name};
         return student;
        }

    }
    console.log(createStudent('Ken'));
    console.log(student);
})();

2 Answers

Tray Denney
PLUS
Tray Denney
Courses Plus Student 12,884 Points
Tray Denney
Tray Denney
Courses Plus Student 12,884 Points

The problem seems to be that you are trying to create a second student variable. You can reassign the variable by removing the let in your if statement.

(function (){
    let student = {name: 'James'};
    function createStudent(name){
        if(true){
         student = {name: name};
        }
        return student;
    }
    console.log(createStudent('Ken'));
    console.log(student);
})();
Johnny Garces
Johnny Garces
Courses Plus Student 8,551 Points

Yes, I am trying to create a second student variable that's only scoped to the if-statement. Why then does it get assigned to "James"? thx for ur response btw- still confused with es6 variables. I'm surprised Guil from Treehouse didn't go over block-scope, an important concept in es6.

Johnny Garces
Johnny Garces
Courses Plus Student 8,551 Points

yup that did the trick :) is it because if you return a value outside of its block-scope, then it will look up its scope-chain and reference the outer-scope's value? (in this case, the outer-scope being the function scope...)?

thanks again!

ywang04
ywang04
6,762 Points
ywang04
ywang04
6,762 Points 
(function (){
    let student = {name: 'James'};
    function createStudent(name){
        if(true){
         let student = {name: name};    
        //this student variable with let keyword which has it's own block scope. 
        }
        return student;  
//this returned student variable is not the same as above one due to block scope, actually 
//it refers to {name: 'James'} using scope chain
   }
    console.log(createStudent('Ken'));
    console.log(student);
})();

To meet your requirement

(function (){
    let student = {name: 'James'};
    function createStudent(name){
        if(true){
         let student = {name: name};
         return student;     //put return statement in "if" block scope
        }
    }
    console.log(createStudent('Ken'));
    console.log(student);
})();