Short guide explaining how to send data from iframe p5 sketches to a host webpage

This examples doesn't utilize a web bundler, check out branch complex-vite+pnpm for a variation using vite.js and pnpm.

To try this example, spin up a local webserver, e.g. using npx

• index.html is the main web page which includes a sketch via iframe
• index.js is the main JavaScript file handling Window.postMessage from the iframe and switching the background color via CSS variables
• index.css is the stylesheet of the main pages. Defines the CSS variable --color-background which is changed when receiving messages from the iframe
• extern/ holds the external p5 sketch files. This is basically the webpage which will be linked via iframe