A naive and basic implementation of the Diffie-Hellman key exchange to more easily understand how the math works

diffie-hellman.js

// Diffie-Hellman asymetric key exchange allows two
// parties to cooperatively create a shared secret
// key without ever exchanging the shared secret.
// This means that it will be nearly impossible for 
// a malicious party observing the creation of the 
// shared secret to determine the secret key.

// Randomly create a generator number and a number p
// These two numbers are shared between both parties 
// in the public space which means they're potentially
// accessible to a malicious party. I'm not following
// the Diffie-Hellman parameter requirements but the
// math still checks out.
let g = 10;
let p = 20;

// The two parties wanting to communicate should generate
// their own private keys. These keys are never exposed
// to the public space. These numbers can be generated
// randomly.
let privateAlice = 4;
let privateBob = 5;

// Each party computes it's own public key by taking the
// private key raised to the generator and applying modulo p.
let publicAlice = (privateAlice^g)%p;
let publicBob = (privateBob^g)%p;

// Each party exchanges public keys and then computes a
// shared key by raising the private key to the other
// party's public key and then applying modulu p. 
// Mathematically this produces the same number and now
// both parties have a shared secret that was exchanged
// without ever exposing the secret in the public space.
let sharedAlice = (privateAlice^publicBob)%p;
let sharedBob = (privateBob^publicAlice)%p;

console.log(sharedAlice, sharedBob);