JavaScript interop

Grounded operations let MeTTa call your TypeScript functions. The JavaScript interop layer goes one step further: it lets MeTTa reach into the host runtime itself, calling global functions and methods and building JavaScript values, with no glue code. Enable it with registerJsInterop.

import { MeTTa, registerJsInterop } from "@metta-ts/hyperon";

const metta = new MeTTa();
registerJsInterop(metta);

js-atom: resolve and call a global

js-atom takes a dotted path to a global and gives you back something callable:

!((js-atom "Math.abs") -5)        ; 5
!((js-atom "Math.max") 3 7 2)     ; 7

An unresolvable path is a hard error (a MeTTa (Error ...) atom), not a silent undefined, so a typo surfaces immediately.

js-dot: call a method on a value

js-dot reads a method bound to its receiver and calls it:

!((js-dot "hello world" "toUpperCase"))   ; "HELLO WORLD"

js-list and js-dict: build JavaScript values

js-list builds a JavaScript array and js-dict a JavaScript object, both usable by host methods:

; Array.prototype.join over a js-list
!((js-dot (js-list (5 1 3)) "join") "-")    ; "5-1-3"

; read a field of a js-dict
!(js-dot (js-dict (("a" 1) ("b" 2))) "b")   ; 2

When to use which

Use a grounded operation (registerOperation) when you want to expose a specific, named TypeScript function to MeTTa with control over its behavior. Use js interop when you want MeTTa scripts to drive arbitrary host APIs directly, for quick glue or scripting. Both convert between atoms and JavaScript values with atomToJs / jsToAtom, which you can also call yourself.

That covers the TypeScript interop story. To write MeTTa in idiomatic, typed TypeScript rather than source strings, see the typed eDSL.