preload.js

// Everything here is evaluated at build time and serialized into the snapshot.
// jsvm starts with it already on the heap: no parse, no compile, no allocation.
//
// Good candidates: polyfills, validation helpers, parsers, any pure-JS library
// your scripts always need.
//
// Will NOT survive snapshotting:
//   - anything holding a host object or external pointer not listed in
//     kExternalReferences
//   - open handles, timers, pending network state (none of which exist here)
//   - Date.now() / Math.random() results you expect to be fresh, since they
//     are frozen at build time

globalThis.jsvm = Object.freeze({
  version: '0.1.0',

  // Structured output for callers that parse stdout.
  emit(value) {
    print(JSON.stringify(value));
  },

  assert(condition, message) {
    if (!condition) throw new Error(message || 'assertion failed');
  },
});

// Deterministic deep clone that predates structuredClone in some builds.
globalThis.clone = function clone(value) {
  return JSON.parse(JSON.stringify(value));
};