do...while scoping issue when initializing variables inside of body

Question

Was having some fun with prompt, parseInt and do...while and just stumbled upon the following:

do {
    let length = prompt('Enter a number between 8 and 128 (inclusive) for your length.');
    length = parseInt(length, 10);
} while (length < 8 || length > 128);

Every time I would use the Chrome Developer tools to inspect the value of length during the while execution, I would see a value of 0. I thought there was something up with the radix I had chosen for parseInt but that was not the case.

I noticed that VS Code was complaining that the let length was not being used anywhere. That was odd. Once I removed the variables outside of the loop and declared as separate string and number fields instead, (i.e., let lengthPrompt and let length), everything worked out:

let lengthPrompt;
let length;

do {
  lengthPrompt = prompt('Length?');
  length = parseInt(lengthPrompt, 10);
} while (length < 8 || length > 128);

Is this an issue with scope or some other weird JS specific thing I am unaware of.

`let` has block scope, so in your first code, `let` does not exist after the `}` of the `do` — CertainPerformance, Mar 16 '20 at 01:49
yet `let` in `for(let x` is before `{` but is in scope only inside the body (not after the for loop) :p javascript inconsistent as ever — Jaromanda X, Mar 16 '20 at 02:08

do...while scoping issue when initializing variables inside of body

0 Answers0