Status: refused by design
Math is not FunctionalScript. Math is valid JavaScript, and fjs compile refuses it by design: the demo below shows what it prints.
A FunctionalScript module has no free names: everything it reads it binds or imports. JavaScript's globals, Math, JSON, globalThis, Promise and the rest, are no exception, so a name no const, parameter or import binds is refused (const not found). The few built-ins the language admits, such as Number, String and Object.is, are recognized by name (built-ins).
The row name.unbound of refused constructs registers the refusal, and global names gives its reason.
export default Math.max(1, 2);
The demo on this page compiles sample.mjs, the module above, with this build's fjs compile, and shows the line it prints and the token it refuses. Below that it shows what JavaScript answers for the same module: 2.
Write the function, or import it from a module, as alternative.f.js does:
/** @type {(a: number, b: number) => number} */
const max = (a, b) => a < b ? b : a;
export default max(1, 2);
It answers 2.
Today fjs compile prints const not found at the refused token. The demo proposes what it should print instead: the reason at the same token, what JavaScript does there, and the allowed spelling, the line alternative.f.js writes, as help. The page compiles the alternative too, so the suggestion is one the compiler accepts.