Mador

The minified runtime weighs 855 bytes. mador.js adds reactive state to DOM that already exists on the page. Calling mador() hands back a read function and a write function, and only the bindings that read a changed value run again, batched per write. No components, no templates and no virtual DOM: it loads as an ES module from npm or a CDN with no build step, and a binding is dropped once its elements leave the page.