Listing Prime Numbers in JavaScript for Kids

Randomness of Prime Numbers | Maths Explanation for JavaScript Kids

Prime numbers are natural numbers greater than 1 with no positive divisors other than 1 and itself. Prime numbers, in ascending order, are:

2, 3, 5, 7, 11, 13, 17, 19, 23, ...

Because prime numbers are so random in their progression, they are very difficult to predict as they get larger.
For the reason of their unpredictability, prime number are applied in

Cryptography: RSA encryption relies on large prime numbers.
Hashing: Prime numbers help reduce collisions in hash functions.
Data structures: Primes are used in sizing hash tables and optimizing algorithms.

In this beginner-friendly Maths JavaScript tutorial for kids, we'll show how to list prime numbers in a fun and interactive way for STEM students.
Writing a JavaScript code to list prime numbers will involve checking every number in a range of interest and gathering those that are without factors.

Logic for Determining Prime Numbers | Detailed Explanation for JavaScript Kids

Say we want to implement a JavaScript algorithm to list all prime numbers between 2 and 100 inclusive, we would start from 2; check to see whether it has any factors; keep it as a prime number if it has no factors; otherwise discard it.
We would then go to 3, and repeat the same process.
Repeat same for 4, 5, 6, 7, ..., 98, 99, 100.

But we can always use a few tricks for the JavaScript algorithm...

We will take the following steps:

Step 1:

First, we'll start our range from 9 (keeping 2, 3, 5, and 7 as prime numbers).

Step 2:

Next, we'll only check through odd numbers.

Step 3:

Next, we'll check against the factors 2, 3, and 5.

Step 4:

Lastly, we'll check with a subset of smaller prime numbers that we'll gather as our check progresses.

Create 2 new files; On Notepad++: File, New.
Call them PrimeNumbers.html and PrimeNumbers.js.
Type out the adjoining JavaScript code that lists prime numbers.

So! JavaScript Fun Practice Exercise - List Prime Numbers

As a fun practice exercise, feel free to try out your own boundary values, and see how the JavaScript code lists the prime numbers between those boundary values.

JavaScript Code for PrimeNumbers.html

<!DOCTYPE html>

<html lang="en">
    <head>
        <meta charset="utf-8" />
        <title>Listing Prime Numbers</title>
        <script src="PrimeNumbers.js"></script>
    </head>
    <body>
        <h4>
            Prime numbers are numbers that can only be divided by themselves and 1
            without remainder.<br />Here is a list of them (between 1 and 99 inclusive).
        </h4>

        <div id="my_primes"></div>

        <script>
            /*
            * The array variable prime_numbers has our prime numbers.
            * Use the array method 'join' to display the values.
            */
            document.getElementById("my_primes").innerHTML = prime_numbers.join(", ");
        </script>
    </body>
</html>

JavaScript Code for PrimeNumbers.js

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