JSFiddle - React, Tailwind, and code Playground

HTML

<img id="main-img" src="" width="100px" height="100px"/>
<button type="button" id="next-btn">Next</button>

JavaScript

const realUrl = window.location.href;
const fakeUrl = "https://mysite.com/base/a.png";
const fakeUrlParts = fakeUrl.split("/");
const cloudinaryBasePath = "https://res.cloudinary.com/dq7jxbdhj/image/upload/v1576378663";
const imgDisp = document.getElementById('main-img');
imgDisp.src = cloudinaryBasePath + "/" + fakeUrlParts[3] + "/" + fakeUrlParts[4];

const nextBtn = document.getElementById('next-btn');
let showA = true;

nextBtn.addEventListener('click', () => {
	if (showA) {
  	showA = false;
    imgDisp.src = cloudinaryBasePath + "/" + fakeUrlParts[3] + "/" + 'b.png';
  } else {
  	imgDisp.src = cloudinaryBasePath + "/" + fakeUrlParts[3] + "/" + 'a.png';
  	showA = true;
  }
});