js

JS-value interop for the nimony JavaScript backend.

The backend lays native Nim data out as byte offsets into one linear ArrayBuffer; a genuine JS value — a string, object, function or DOM node — can't live there. JsValue is an opaque handle into a runtime-side value table, so real JS values cross that boundary. It is the substrate aoughwl's client-side packages (web-state, and the DOM/web client runtime) sit on.

import jsffi

let math = global("Math")
echo math.call("max", toJs(3), toJs(7)).toInt      # 7

let o = newJsObject()
o.set("name", toJs("nimony"))
echo global("JSON").call("stringify", o)           # {"name":"nimony"}

What you get

• JsValue — an owning handle to a JS value. GC-integrated: =destroy releases its table slot, and a copy allocates a fresh slot to the same value, so handles copy and free without ceremony and never double-free.
• marshalling — toJs / toInt / toFloat / toBool / $(stringify) for int/float/bool/string (strings cross as UTF-8).
• access — global, get/set, call (0–3 args) and variadic apply, newJsObject, new-construction (newOf), JS arrays (newJsArray/add/[]).
• introspection — jsTypeof, hasProp, instanceOf.
• callbacks — a Nim proc {.nimcall.} as a JS function (toJs(JsProc0/1)), the shape of an event handler.
• unsafeHandle / unsafeFromHandle — the raw-handle seam a higher layer (web-state, a DOM binding) uses to marshal a JsValue across its own runtime boundary without re-implementing the ARC hooks.

Runtime

The Nim side is standard-library-only; the runtime bridges (the value table and the _jsGet/_jsCall/_strToJs/… functions the importc procs name) live in runtime/jsffi.js, linked into the JS bundle by the backend. Reading the raw FFI seam is kept on plain int32 handles, so no owning JsValue ever crosses into an importc.

Status

Prototype, tracking the nimony JS backend (nim-lang/nimony#2043). tffi exercises the surface end-to-end (./run.sh, with the backend toolchain on BIN). Once the backend lands std/jsffi, this becomes a thin shim over it.

License

MIT.