My solution to a challenge was very different from the instructor's solution. What is the disadvantage in my version?

Congratulations on passing the challenge! That's totally worth some cred up front. It definitely takes time basking in JavaScript to appreciate different advantages of one approach over another. In fact, that's one of the hardest, and most rewarding things about JavaScript: there are many, many ways to accomplish the same results.

In general, these are some good-making features of any solution:

1. It's easier for a human to understand what the code does when they read it.
2. It's shorter (as long as (1) is respected).
3. It produces the desired result faster.
4. It requires less memory.

There are many other things to strive for when writing good code, but these are probably the most pressing. Up for debate, but the above conditions are probably also in order of importance. The number one most important thing about your code (besides making it produce the effect you want) is that it is clear how it works to a HUMAN reader. Usually that will be YOU in the future, trying to decipher what you did in the past.

Employing these criteria, here are some reasons to prefer the instructor's code over the code you wrote.

• The instructor's is easier to read. For example:

Your code:

var totalPoints = 0; 
var question1Point = 0; 
var question2Point = 0; 
var question3Point = 0; 
var question4Point = 0; 
var question5Point = 0;

What are all of these variables for? Their names are not clearly legible, they have numbers in the middle, there are a whole bunch of them in a row, they all have the same value. What are they all for? Compare that to the instructor's code:

// quiz begins, no answers correct
var correct = 0;

// ask questions
var answer1 = prompt("Name a programming language that's also a gem");
if ( answer1.toUpperCase() === 'RUBY' ) {
 correct += 1; 
}
var answer2 = prompt("Name a programming language that's also a snake");
if ( answer2.toUpperCase() === 'PYTHON' ) {
 correct += 1; 
}

Ok, here we see that there's one variable saving the number of correct answers, and it gets bigger for each correct answer. Crystal clear!

• The instructor's is shorter, without sacrificing legibility. For example:

Your code:

var totalPoints = 0; 
var question1Point = 0; 
var question2Point = 0; 
var question3Point = 0; 
var question4Point = 0; 
var question5Point = 0;

Don't all of these variables really just describe how many points you have? Why not just have one master points variable that gets bigger when certain conditions are met? Compare that again:

// quiz begins, no answers correct
var correct = 0;

6 lines > 2 lines.

• The instructor's code requires less memory. In this case it's not noticeable at all, because the script is so small. But every one of these variable assignments requires a chunk of RAM for its own safekeeping. If you see var, that's eating memory. In general, it's good to use less memory if some alternative is equally legible, and performs as well.

• The instructor's code is faster. It's a big topic about why, but to begin with: his code is short, so there's less code to run, so it's faster. That's not a universal truth, but it's a good rule of thumb for your beginning scripts.

Sometimes programmers refer to "DRY" code. It's an acronym that stands for "Don't Repeat Yourself". DRY code typically respects the four conditions of good code that I described above. You can see that your solution - while it works - isn't very DRY. There are lots of variables being created, when you could get by with many fewer.

The solution you've written is also not easily updated. Suppose you wanted to add other questions to the series. Your solution requires that you add new variables to the code for all of the possible answers and scores. That would be annoying, and it's not easily scalable (it doesn't get infinitely bigger easily). The instructor's code is much easier to append new questions to. It requires fewer changes in the code for any one change in the series. That means less work for you later. That's better.

Does that answer your question? If so, please up-vote my answer as "Best Answer"! It helps me reach my career path goals quickly. If not, feel free to write more!