A little experiement with seeing how complex of an app I can store entirely within a url.

The basic idea revolves around the fact that a data urls can define their encoding as text/html.

i.e data:text/html;charset=utf-8,hello%20world is a valid url (try pasting it in your url bar).

So is data:text/html;charset=utf-8,%3Cstyle%3E%20*%20%7B%20color%3A%20red%3B%20%7D%3C%2Fstyle%3EHello%20world!.

Aditionally, so is data:text/html;charset=utf-8,%3Cstyle%3E%20*%20%7B%20color%3A%20red%3B%20%7D%3C%2Fstyle%3EHello%20world!%3Cscript%3Ealert(%22hello%20again!%22)%3B%3C%2Fscript%3E.

So, if we can put html, css and js in a url and have that render a valid html page, how much of a page could we create?

I've come up with a 1033 852 799 713 byte solution that is a fully playable game of snake.

let e=document.body,t="Space: start/reset. Arrows: Move<div><canvas id=a><style>#a{border:solid}*{background:tan}</style>",r=40,n=400,o,d=[[4,3]],s=d[0],c="#000",p=(e="red",t=n,a=0,l=a)=>{C[f="fillStyle"]=e,C.fillRect(a*r,l*r,t,t)},h=(e,t=n/2,a=t,l="center")=>{C[f]=c,C.textAlign=l,C.fillText(e,t,a)};e.innerHTML=t,C=a.getContext`2d`,a.height=a.width=n,C.font="30px f",e.onkeyup=({which:e})=>{36<e&&e<41?H=e-38:32!=e||o||(o=1,d=[[4,3]],H=2,S=0)},setInterval(i=>{if(o){let[e,t]=d[0],a=e+H%2,l=t+(H-1)%2,n=([e,t])=>e==a&&t==l;if(d.pop(),a<0||9<a||l<0||9<l||d.some(n))return o=0,p(),h`:(`;d=[[a,l],...d],n(s)&&(d[++S]=d[S-1],s=[(D=new Date)%10,D*S%10]),p`tan`,d.map(e=>p(c,r,...e)),p(i,r,...s),h(S,9,30,"left")}},n);

Encoded as a url it is 1152 bytes long:

data:text/html;charset=utf-8,%3Cbody%3E%3Cscript%3Eeval(atob(%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%22))%3C%2Fscript%3E

You can paste that url into your browsers address bar, or checkout the minified html running here (or here for a mobile compatible version)

I'm super happy with some of the code golfing techniques I've used in this code and have tried to leave comments explaining most of them. I'm especially proud of:

//...
headings = {37:1,38:1,39:1,40:1},
// ...
update = () => {
  if (!alive) return;
  let [headX, headY] = snake[0],
    nextX = headX + (heading)%2,
    nextY = headY + (heading-1)%2,
    collides = ([x,y])=> (x ==nextX&&y==nextY);
//...
d.onkeyup = ({ which: w }) => {
  headings[w] ? (heading=w-38) : w==32 && !alive && reset();
};

If you want to just see the annotated golf'd code, take a look at golf/dev.html

This repo contains two sets of code, one for a mobile compatible version and one just for maximum code golfing

/
  run.js         - node script that generates minified files and outputs data urls
  dev.html       - dev file for mobile snake
  index.html     - minified version of mobile snake
  /golf
    dev.html     - dev file for code golf'd snake
    index.html   - minified version of golf'd snake

To develop on either one you can run the yarn install to install the dev dependencies and then yarn build to build both versions. This will output a dist directory like so

/dist
  index.html    - minified version of compatible snake
  golf.html  - minified version of golf'd snake

and also update both index.html files.

If developing on a single file, use the run.js script directly from whichever dir you are working on.

$ node run.js
data:text/html;charset=utf-8,%3Cbody%3E%3Cscript%3Eeval(atob(%22bGV0IGU9ZG9jdW1lbnQsdD1lLmJvZHksbD1NYXRoLHI9IlNwYWNlOiBzdGFydC9yZXNldC4gQXJyb3dzOiB...

$ cd golf
$ node ../run.js
data:text/html;charset=utf-8,%3Cbody%3E%3Cscript%3Eeval(atob(%22bGV0IGU9ZG9jdW1lbnQsdD1lLmJvZHksbD1NYXRoLHI9IlNwYWNlOiBzdGFydC9yZXNldC4gQXJyb3dzOiB...

To get more debug information, add the DEBUG flag

$DEBUG=1 node run.js
{
  js: 'let e=document,t=e.body,l=Math,r="Space: start/reset. Arrows: Move<div><canvas id=a><style>#a{border:solid}*{background:tan}</style>",n=40,o=400,i,d,f=[[3,3]],s= ...',
  jsLength: 852,
  minifiedLength: 852,
  encodedLength: 1136,
  minifySaved: 0,
  urlLength: 1220
}
data:text/html;charset=utf-8,%3Cbody%3E%3Cscript%3Eeval(atob(%22bGV0IGU9ZG9jdW1lbnQsdD1lLmJvZHksbD1NYXRoLHI9IlNwYWNlOiBzdGFydC9yZXNldC4gQXJyb3dzOiBNb3ZlPGRpdj48Y2FudmFz ...

To automatically open the data url in chrome, you can use xargs:

$ node run.js | xargs open -a "Google Chrome"