gbajs2 is a Game Boy Advance emulator written in Javascript from scratch using HTML5 technologies like Canvas and Web Audio. It is freely licensed and works in any modern browser without plugins.
How it's currently implemented is you would have to go to /debugger.html... though I'm not sure it works in gbajs2. I think some "renderers" support it and others do not.
What is the debugger and console? And how do you use it? Thank you!