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JavaScript JavaScript Basics Storing and Tracking Information with Variables Update the Value of a Variable

Gavin Lefleur
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Gavin Lefleur
Full Stack JavaScript Techdegree Student 742 Points
Posted by Gavin Lefleur
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Gavin Lefleur
Full Stack JavaScript Techdegree Student 742 Points

Help - TypeError for challenge 1 (Full stack Tech Degree - JS)

Hi Guys,

I am getting a 'Type error' using let command for one of the challenges in JS. Can anyone explain to me why?

app.js 
let points = 100;
let bonusPts = 50;

let points += bonusPts;
console.log(points);
Gavin Lefleur
seal-mask
.a{fill-rule:evenodd;}techdegree
Gavin Lefleur
Full Stack JavaScript Techdegree Student 742 Points
Gavin Lefleur
.a{fill-rule:evenodd;}techdegree
Gavin Lefleur
Full Stack JavaScript Techdegree Student 742 Points

The original code and question is below:

Evaluate the code in app.js. The code currently produces a TypeError. Adjust the code so that the points variable holds the expected value.

const points = 100; const bonusPts = 50;

points += bonusPts; console.log(points);

2 Answers

jb30
jb30
44,807 Points
jb30
jb30
44,807 Points

You can't redeclare values with let in Javascript. let points += bonusPts; should be points += bonusPts;.

jb30
jb30
44,807 Points

The line let points += bonusPts; gives a syntax error. It is the short form of let points = points + bonusPts;, which requires points to already have a value on the right side and using it to compute the value for points on the left side. Since let is used to declare a variable for the first time, I would expect there to be a syntax error when you try to declare it using its own value, since if it already has a value, you have already declared the variable.

While all of my browsers agree that using let with += is a syntax error, they disagree on whether let points = points + bonusPts; is also a syntax error. If you don't know what browser your code will be run in, relying on redeclaration of your variables using let could be an issue.