How to code (How to write Worlds and Minds)

You can write your own Minds and Worlds. They are hosted on this server.

You need to register and login to write your own Minds and Worlds.


All Worlds and Minds are written in JavaScript. They all run on your machine in the browser (not on the server).

All Worlds and Minds can be written in the browser. No install is needed to write them or run them.

JavaScript is an important programming language. It is the dominant language on the Web on the browser side (and also important on the server side). Some surveys rank it as the most important programming language in the world. It is a valuable skill for a tech career.

Edit in browser

To edit code in the browser, we use the Ace editor. This does JavaScript syntax highlighting and syntax checking.

Run from editor

You can run direct from the editor using the "Run" button. But note it runs the saved version, not the text currently in the editor (if not saved).

Outputting debug information

You can output debug information to:
  1. The JavaScript console (in the run window). You can use console.log();
  2. The user_span status areas in the run window. ("View Source" on a run to see these.)
  3. Creating new divs in the window. See the following.

Outputting arbitrary amounts of data

You can output arbitrary amounts of data. Let us say you are running an AI learning experiment and want to output the Mind's data structure after a long Machine Learning run. Do this:
  1. Create a new div using document.createElement('div') and append it to the page.
  2. Use CSS to put it in the foreground and give it a scrollbar.
  3. Output your data to the div.

Saving data to the server

You can also save data to the server.

Obfuscate your JavaScript

The nature of JavaScript is that the source code is visible, so this site supports built-in obfuscation for those who want to hide their code.

If you want to make it difficult for people to copy/modify your code, you can save the JS in an obfuscated (also minimised) form. The obfuscated JS is the version visible online, and the version that runs when you click Run. The plain text JS is saved on our server. When you Edit, the plain text version is always loaded. Only the owner can see this.

Obfuscation is optional and is off by default. When you Edit, you will see an option like the following to save the public JS in an obfuscated form or in plain text:

Trying to de-obfuscate someone's obfuscated JS is against our terms of use.

Include another JS file

You can include another JS file in your code. This can be a local (on our server) or remote JS file. Include it like this:


The JS script is loaded from SOMEURL. This is asynchronous. At some point it returns and SOMEFUNCTION is called. Your code elsewhere may need to check if the JS is loaded yet or not.


  • Do not put the World definition or Mind definition inside SOMEFUNCTION. They must be in the global namespace.
  • Need to avoid mixed content. The run is HTTPS so remote JS must be HTTPS.

Examples of including another JS file:

  • Mind calling a Mind. Mind is defined outside of SOMEFUNCTION. SOMEFUNCTION sets a variable to show the JS is now loaded. Mind's getAction method repeatedly checks that variable to see if the JS is loaded yet.
  • Code of Purple Fruit Monster. This is a port of some JS that does not use a World class or Mind class at all. It just needs a JS library loaded before the main JS runs.
  • See jQuery getScript docs for more examples.

Multiple JS files

To break up your code into multiple JS files, upload the extra JS files into your "Uploads" section. You can edit them online with the "Edit" button on the Uploads page.

Your main World or Mind JS file can then include those other JS files as described above.

Worlds and Minds do not have to be on this site

Following on from the above, Worlds and Minds do not have to be on this site. You can develop Worlds and Minds on your own site, with your own development tools. So long as they are JS at some URL. You can then upload a stub World or Mind to this site which drags in the JS from your site at run-time. This relates to The AI model behind this site.

The background is a program, showing the JavaScript graphics used on this site.

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