One of the problems is that the case where you check `i % 15`  (i.e. `i` is a multiple of 3 and 5) is unnecessary. You have the concept of 3 and 5 repeated, and the concept of Fizz and Buzz repeated.

This is not currently much of a problem but suppose someone asks you to extend your program to print "Jazz" when `i` is a multiple of 7. Using your current strategy we now need a case where `i` is a multiple of:

 1. 3
 2. 5
 3. 7
 4. 3 and 5
 5. 3 and 7
 6. 5 and 7
 7. 3 and 5 and 7

It would look something like this:

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

    for(var i = 1;i <= 100; i++) {
        var output = "";
    
        if(i % 105 == 0) {output = "FizzBuzzJazz"}
        else if(i % 15 == 0) {output = "FizzBuzz"}
        else if(i % 35 == 0) {output = "BuzzJazz"}
        else if(i % 21 == 0) {output = "FizzJazz"}
        else if(i % 3 == 0) {output = "Fizz"}
        else if(i % 5 == 0) {output = "Buzz"}
        else if(i % 7 == 0) {output = "Jazz"}
        else { output = i; }
    
        console.log(output);
    }

<!-- end snippet -->

See how quickly that got out of hand? If we add a fourth word it becomes even worse.

If we use a different strategy by *appending* text to the `output` variable, we can get away with having as few conditions as we have words.

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

    for(var i = 1; i <= 100; i++) {
        var output = "";
        if (i % 3 == 0) {output += "Fizz"}
        if (i % 5 == 0) {output += "Buzz"}
        if (i % 7 == 0) {output += "Jazz"}

        console.log(output == "" ? i : output);
    }

<!-- end snippet -->

On thing that might be new to you here, if you're a beginner, is that the expression used as the argument for `console.log` or called the [*conditional or ternary operator*][1]. Ours says that if the output is blank (i.e. not a multiple of 3, 5 or 7) then print `i`, else print the string that we've compounded.

The ternary operator can always be replaced by an if-statement if you're not yet comfortable with it.


  [1]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_Operator