This project started as a simple “shower thought”. Could I build jsFiddle inside jsFiddle?

After a few minutes of “fiddling”, it was clear that the answer was Yes! Below is the crude code of that first iteration. No idea for how long, but the original fiddle can be found HERE.

Prototype Code


<button id="run" onclick="runContent()">run</button>

<div class="box">
    <div class="col">
        <textarea id="html"></textarea>
        <textarea id="javascript"></textarea>
    <div class="col">
        <textarea id="css"></textarea>
        <iframe src="" id="frame"> </iframe>


var frame = document.getElementById("frame");
var mu = document.getElementById("html");
var js = document.getElementById("javascript");
var css = document.getElementById("css");

function runContent() {
    frame.src = "data:text/html;charset=utf-8," + getContent();

function getContent() {
    return `


textarea {
    height: 300px;
    width: 100%;

iframe {
    position: relative;
    margin: 0;
    padding: 0;
    height: 300px;
    width: 100%;

.box {
    display: grid;
    grid-column-gap: 8px;
    grid-template-columns: auto auto;

.col {
    display: grid;
    grid-row-gap: 8px;
    grid-template-rows: auto auto;


Now there are some obvious limitations with this implementation. For starters, there is no syntax highlighting. It is a very crude implementation. But more important that any of that is that it worked. I was able to effectively reverse engineer a concept used for many sandbox sites like jsFiddle and codepen. I have been a long time fan of jsFiddle and have utilized it to prototype many projects.


With this prototype proofed out, the obvious next step was for me to build my own prototyping/sandbox application. Using Vue.js, ace, highlight.js, and other libraries to build out the sandbox implementation.


With the sandbox implemented, it was easy enough to create an in-browser markdown editor and renderer.



To allow for persisting of sandbox code, I created a backend using Strapi is a fantastic headless-CRM for developing backend APIs very quickly.


I thought that it would be nice to extend's functionality to allow for code compilation and and execution right in the web browser. I built out a another backend service written in Golang to facilitate this.

Currently, it supports Golang, Ruby, Python, and Nodejs. As it is currently implemented, it should be very simple to add support for other languages in the future.


Last but not least, I thought it would be awesome to expose a full-fledged Linux terminal right in the browser. Similar to the codebox, I created a backend service that will spin up a docker container and expose the I/O to the frontend via WebSockets. I had never had a chance to utilize WebSockets before so this was a great learning experience for me.

Checkout and feel free to send me feedback at