Either array iteration or string conversion problem

@Steven Parker can you explain why moving lightLevel outside the loop worked? I am not sure what I did but nothing would work for me until I set the initial value of lightLevel and lightItem to 0.0.

It seem that if you don't set lightLevel equal to 0 to start it will return NaN. I have been looking though MDN and cannot figure out why.

Steven,

javascript does not have block level scope. It only has global and function level scope.

So even if the variable is declared inside the loop, the declaration is hoisted to the top of either the global code or the top of the function if this code is within a function. It's a best practice to declare variables at the top but doing it inside the loop wouldn't cause any issues.

The following code runs perfectly fine but not a good practice since you're relying on the hoisting instead of being explicit about it.

lightLevel = 0;

for (var i = 0; i < 10; i++) {
  var lightLevel;

  lightLevel += 5;
}

console.log(lightLevel); // 50

I think the only issue was the uninitialized variable.

Shawn,

lightLevel is undefined the first time lightLevel += itemLight; is reached. It's been declared but hasn't been given a value yet.

You're trying to do something like lightLevel = undefined + 5.0; the first time through the loop. This results in NaN being assigned to lightLevel

Next time through the loop you have something like lightLevel = NaN + 3.0 Any calculations with NaN continue to result in NaN. lightLevel is therefore stuck at NaN for the rest of the loop.

Awesome! Thanks Jason!

As I understand it, "hoisting" is only applied to function declarations, not to variable declarations.

Hey Steven,

Are you getting to some old notifications here? :)

I'm pretty sure that you do have variable hoisting with the var keyword at least. This doesn't apply anymore with let and const

I don't know if you had a chance to try the code in my comment but I don't think it would be able to log 50 if there was block level scope. In my example, if you replace the var keyword with let then you'd have 2 lightLevel variables. A global one and one local to the loop.

In that case, it logs 0.

The same thing happens with the index variable even though I used the var keyword in the for statement. You could log the value of i after the loop and it would be 10. What's happening behind the scenes is more like how you and Bryan wrote it, with var i; at the very top.

It's certainly better to write the code the way you did in your answer and not how I have in my previous comment but they would both work the same way.

After looking it up I see that "JavaScript only hoists declarations, not initializations." I wasn't previously aware of that, partly because I very rarely declare without initializing, and as matter of practice never assign before declaring.

I love how contributing to the forum leads to learning things I might never know otherwise.

Yes, I've certainly learned a lot from your answers as well as others.

I'd say this variable hoisting is probably one of the quirks of javascript that can lead to a lot of confusion with beginners.

I think it's a good thing that we'll be moving on to using let and const and at least in this respect it will work more like what we're used to with C-like languages.