Hi and welcome to the art of programming!

I started writing a longer answer but saw that @mindriot already answered. Like @mindriot I also think you got the looping right but were confused by the decision logic inside of it.

Programming can be quite abstract and it can sometimes help to try to reframe the problem into something more tangible. Maybe this helps or gives inspiration to future problems:

Say that you have a group of people in a large room and you want to give them each a clothing item depending on their color preferences. A red t-shirt with the logo Fizz if they like red, a blue hat with the logo Buzz if they like blue and both the t-shirt and the hat if they like both colors.

You put them in a line (the for loop) and start with the first person who happens to only like red. When asked “Do you like red?” and answer “Yes!”, the person is given a red t-shirt.

You then move to the next person and ask the same question:

“Do you like red?”
“No, I really don’t”
“Do you like blue?”
“I do!”

At this point a blue hat is given out and you move on to the next person again. The third person in line happens to like both red and blue and is looking forward to be given both a t-shirt and a hat. But when asked:

“Do you like red?”
“I do…”

Imagine the dissapointment when you hand out a red t-shirt and move on.

“If only they had asked the questions in a different order”, the third person mutters and reluctantly puts on the t-shirt.

Similarly, to apply the same metafor to the authors implementation. In this scenario instead of handing over the merchandise directly upon an affirmative response, the item is put in a bag (output) where multiple items can be put before handing it over.

Ie. something along the lines of:

1. The questioner prepares an empty bag (let output = "").
2. “Do you like red?”, “Yes!”. A red t-shirt is put in the bag. (output += "Fizz")
3. “Do you like blue?”, “Yes!”. A blue hat is put in the bag. (output += "Buzz")
4. The bag is handed over containing a red t-shirt and a blue hat.
   (console.log(output)).

(BASHES HEAD AGAINST DESK.)

I know this… Why didn’t I notice… UGH. I guess I should have just stepped away and came back to it. Ugh… Now I feel REALLY dumb. The author doesn’t mention it in his book but, I remember it from other books I’ve read.

What if I need to increment more than 1 at a time? Do I just add more + symbols? Or I just need to do the long form like n = n + 2?

I know about the arithmetic use and the concatenation use. But… The others…

output = output + “Fizz” to me makes perfect sense…

output += “Fizz”… That makes sense now that you’ve explained it. Wish the author explained it before using it. Lol.

What? You lost me.

I think I remember him mentioning this in the chapter I read.

The example I think he gave was something like this…

“dog” === “cat”
and it evaluates to false since the strings aren’t identical and it’s looking for an exact match.

“dog” !== “cat”
and it evaluates to true since they are the inverse of the previous example.

Did I remember that correctly?

0 is true and false? You lost me again.

The author mentioned this in the first chapter. So far it seems the info in the book is great it’s just the author’s examples that are causing confusion.

Yes! ok! That is much easier to understand and read. Kinda wish the author gave me that instead Lol.

Omg yes. COMMENTS! Why the author didn’t provide his example like that is beyond me.

Ok so anytime I am going to invoke a for loop I need to follow the following syntax…

for ( declare variable and assign a value ; ( Don’t really know what you would call this part ); Index Counter Increment. )

In the author’s example there are no if’s, did he use some sort of shorthand method or something?

Good to know I am not the only one. Lol. After I typed up my question I went to the ECMA’s website and downloaded the latest ECMAScript Language Specification and started reading the section on for loops. Lol.

Unfortunately, it seems they also have an issue with describing things in such a way that a non-engineer can actually understand what was written. Lol. I tried to read the syntax it provided but, it wasn’t very clear and they do not provide any examples so it’s difficult to understand what they are trying to say. I am sure if I read the spec from start to finish it would make sense but, right now, I just don’t have the time for that.

You shouldn’t beat yourself up about it, it is very easy to overly focus on one part and completely miss what is really happening. Taking a break to clear your head is usually really helpful in this case. All of us have spent many hours b like this in the past, personally probably amounts to hundreds of hours.

You can use the arithmetic use of += for this, n += 2 or you can write the longer form if you prefer.

I probably shouldn’t have attempted to dive into this and try explain how it works… since we are in that hole now, I’ll give it another shot, if it still doesn’t make sense then don’t worry about it too much for now.

So what I’m talking about here is that there are true and false values which are explicitly true and explicitly false. There are also other values like 1 and "hello" which are neither true or false but can be treated as if they are in some cases, this is often known as “truthyness”. Looking at the slightly clearer if based version of printing the output or n, the use of output as a condition of the if here is depending on the fact that an empty string will be treated as false and conversely a non-empty string will be treated as if it is true.

 if (output) { // <-- when the output here is empty then it behaves as if output is false, if it is not empty it behaves as though it is true
    console.log(output);
} else {
    console.log(n);
}

You can even see this in a simple comparison, "" == false will evaluate to true, "hello" == true will also evaluate to true. The === and !=== versions I mentioned before don’t do this, "hello" === true is false. The version the original author had with output || n is depending in the same way on this implicit way that some values will treated as if they are true and others will treated as if they are false.

You did remember it correctly. These comparisons have 2 versions, these (which have 3 symbols) do a strict comparison that avoids mangling the types of the values and don’t let values pretend to be true/false. They have (generally best avoided) versions with 2 symbols, == and != which are less strict and do mangle types of values.

Sorry for adding to the confusion here. So in this situation that we are discussing where there is a number that is being used in place where a boolean value is expected and it is not a strict comparison (using === / !==) then 0 will be treated as false, other numbers will be treated as true. Here are a couple of examples:

let n = 5;
if (n) {
    console.log("n is not zero");
} else {
    console.log("n is zero");
}

prints “n is not zero”

where as

let n = 0;
if (n) {
    console.log("n is not zero");
} else {
    console.log("n is zero");
}

prints “n is zero”.

The middle part is the stop condition. It should answer the question “should this loop run for the current value of the index counting variable?” with a true or false answer.

We might not be talking about the same code or it might be the way it is formatted. In that part I was meaning about the way the if constructs are used in this code at the start of the commented lines.

for (let n = 1; n <= 100; n++) { 
  let output = "";
  if (n % 3 == 0) output += "Fizz"; // if is at the start of this line
  if (n % 5 == 0) output += "Buzz"; // if is at the start of this line
  console.log(output || n); 
}  

Here is the same code formatted slightly differently that might make the if construct more obvious.

for (let n = 1; n <= 100; n++) { 
    let output = "";
    
    if (n % 3 == 0)
        output += "Fizz";

    if (n % 5 == 0)
        output += "Buzz";
    
    console.log(output || n); 
}  

The main point was that early in the reply I made some comments about how if, else and else if behave in relation to what was going wrong with your solution. I wanted to clarify that those points were not applicable to the authors solution because these are two completely separate if constructs not linked with else or else if. Does that make more sense?

Language specs generally aren’t aimed at beginners, they are mainly a technical reference for people who already have a pretty good grasp on programming and usually are needing to double check a fine detail or are trying to implement a compiler/interpreter for the language.