QBasic in the Browser

A QBasic 1.1 compiler and virtual machine for the web.

QBasic was where many of us wrote our first lines of code. I wanted to bring that familiar blue screen back, so I rebuilt QBasic 1.1 from scratch to run in the browser. Open a .BAS file from 1994 and it just works, from VGA graphics and PLAY music to the original execution speed. I tested it against thousands of real programs running in DOSBox to get the behavior as close to the original as possible. No installation or sign-up required.

To make that possible, I built a compiler and virtual machine entirely in TypeScript. The compiler parses QBasic source code into bytecode, which the VM executes while tracking CPU cycles to approximate the speed of a 486. It also reproduces VGA graphics, PC speaker sound, and DOS-style keyboard and timer behavior. The runtime is independent of the editor, so it can be integrated into other projects too.