The Scripted FizzBuzz Kata
Structure

I'm not quite sure why you chose to write your program the way you did. It seems to add complexity to the naive approach of using a normal function, without adding any benefits:

function fizzBuzzer(number) {
    var isBuzz = (number % 5) === 0;
    var isFizz = (number % 3) === 0;

    if (isFizz &amp;&amp; isBuzz) { return "FizzBuzz"; }
    if (isBuzz) { return "Buzz"; }
    if (isFizz) { return "Fizz"; }

    return number;
}


Misc


parentheses: sometimes you have too many (for example ((isFizz) &amp;&amp; (isBuzz)) would be more readable as (isFizz &amp;&amp; isBuzz)), and sometimes you could use a bit more (for example, to understand var isBuzz = number % 5 === 0;, you need to remember the precedent of 3 things; I would probably change it to var isBuzz = (number % 5) === 0;).
spaces: I wouldn't put a space before ). But I would put one after { and before } to make the code more readable. So if (isBuzz ) {return "Buzz";} for example would become if (isBuzz) { return "Buzz"; }.
I like that you wrote unit tests for JavaScript code. You could also include a test for 0, and maybe negative numbers (as they are allowed as input to your function).