[alphabetter]

I've contributed quite a lot to Paul's simulator, including doing the port so it runs natively in the browser.

The photoresistor is just controlled by the slider in the side-bar. It doesn't respond to lights in the circuit. There is an "optocoupler" under "active building blocks" that does connect optically.

I've seen a few requests to add feedback that occurs outside the electrical domain - light is one, but also for mechanical movement (motors that turn generators). But, I pesonally think it's hard to know how to model all these non-electrical interactions in a way that is visually clear and effective.

[Kiboneu]

Thanks for your contributions. I played circuit.js obsessively during high school (as well as some of the other simulators). It was just way more intuitive than spice. I picked up Art of Electronics around that time.

Ten years later, just the other day I was using it to prototype some filter and resonator circuits.