A function for reactive web UI.

dom, reactive, metaprogramming, proxy, template
npm install s2-engine@1.0.11


test status

s2 is a function for reactive web UI.

See the documentation page for usage details.


See js-framework-benchmark results table.


  • s2.shouldUnmountRoot: enabled by default, but can be disabled. This will automatically call unmount when the DOM nodes mapped to an object are removed. This should only be disabled if you need to keep updating nodes that may be removed and appended later.
  • s2.isDeferred (experimental): this will defer setting proxy values as a microtask. This might be preferable if there is significant blocking in between updates. However, it can break functionality in case there are updates that depend on a previous update in the same tick.
  • s2.window: set a different global object for server-side rendering.
  • s2.debug: turn on messages in the console. Warning: has a performance impact.


s2 is written in the Parenscript subset of Common Lisp.

Need to build the psbuild binary from parenscript-builder and put it here to compile with make. I couldn't figure out how to automate including this dependency yet.


Run automated tests with Deno:

make && deno test test/

Manual testing pages

Run a web server like http-server . and then navigate to the /test/ directory. HTTP is required for loading modules.


s2 is short for simulacra 2. Prior art: I wrote a similar library that is limited to ES5, so no proxies.


BSD 3-Clause