Where a value was written — the file and line of its declaration, or null for one that has no source: a value typed at this prompt, or anything that is not a function.

V8 knows this for functions and for nothing else, so that is the honest limit of it.

The file:line header .doc and .view print, the path .open <value> hands the editor, and what .copy attributes a copied function to — four callers, all asking the same question a reader asks first: where is this written?

import type { ReplSession } from './session.ts';

// Defined, not invoked: a real session owns a browser and a bound port.
async function whereWritten(session: ReplSession) {
  await session.declaredAt('double'); // { file: 'test/fixtures/repl-helpers.ts', line: 15 }

  return await session.declaredAt('GREETING'); // null — a string was never written anywhere
}