Intro to JS - Prime Numbers Example

HTML

<section>
    <!-- We bind to the element's ID using JavaScript --> 
    <button id="myButton">Next Prime Number</button>
    <div id="message-output">2</div>
</section>
<div id="prime-blocks"></div>

CSS

section {
    position: absolute;
    width: 200px;
    height: 200px;
    border-radius: 5px;
    background: rgba(0,20,0,.1);
    text-align:center;
    padding: 15px;
    z-index: 1;
}

section button {
    background: black;
    color: white;
    font-size: 18px;
    outline: none;
}

#message-output {
    display: relative;
    margin: 0 auto;
    font-family: arial;
    font-size: 20px;
    line-height: 100px;
    color: gray;
    text-align: center;
    background: lightgreen;
    width: 100px;
    height: 100px;
    border-radius: 50%;
    margin-top: 15%;
}
#prime-blocks {
    position: absolute;
    top: 0;
    left: 0;
    z-index: 0;
    width: 150%;
    overflow: hidden;
}
#prime-blocks div {
    float: left;
}

JavaScript

//this is a single line comment

/* 
this is a multi-line comment

"the craft of programming is the factoring of a set of requirements into a set of functions and data structures."

Crockford, Douglas (2008-05-08). JavaScript: The Good Parts
*/

//this is a variable to hold prime numbers
//we start with the first prime number, 2
var primeNumber = 2;

/*
What is prime?
A prime number is an integer greater than one whose positive divisors (factors) are one and itself. i.e. 2,3,5,7,11,...
*/

//this a function definition

var getNextPrimeNumber = function() {
    
    /*
    variable values can be passed to other variables
    variables inside a function block within that function's scope
    variables defined outside the function can still be accessed
    */
    
    //other functions can be defined within functions
    
    var calculatePrime = function() {
    
        //increment the prime number by 1
        primeNumber = primeNumber + 1;
        
        //store the value from primeNumber as the dividend
        var dividend = primeNumber;
        
        //use one less than the value stored within the dividend for divisor
        var divisor  = dividend - 1;
     
       //the modulo "%" operator returns the remainder of a division
        
       while(dividend % divisor !== 0) { //loops while condition is met
           
           divisor--; //subtract 1 from divisor and try again
           
           //note* another way to decrement a value by one is to write "val--"
       }
        
       if(divisor !== 1) {
           /*
           If the number is not equal to 1, then we call this function again,
           which increments the primeNumber variable by 1, and tests to see
           if it is prime. This is called "recursion"
           */
           
           //alert('doing recursion');
           calculatePrime();
       }
    }
    
    calculatePrime();
    
    return primeNumber;
}


var myButton =...