vm_script_cachedData.js

// -*- coding: utf-8, tab-width: 2 -*-

const vm = require('vm');

function consLog(...args) { console.log(...args); }

const initSandbox = {
  c: consLog,
  i: 42,
  f: null,
  g: null,
};
const initCode = [
  'i += 1;',
  'console.log("init i:", i);',
  'if (!f) { f = function f() { return i; } }',
  'c("f() inside:", f && f());',
  'c("g() inside:", g && g());',
].join('\n');


function makeSavedState() {
  const sandbox = {};
  const ctx = vm.createContext(initSandbox);
  const script = new vm.Script(initCode);

  script.runInContext(ctx)
  // f() inside: 43
  // g() inside: null

  console.log('initSandbox:', initSandbox);
  // { c: [Function: consLog], i: 43, f: [Function: f], g: null }

  console.log('f() outside:', initSandbox.f()); // 43
  const state = script.createCachedData();
  const encoded = state.toString('base64');
  return encoded;
}

const encodedState = makeSavedState();
console.log('got state:', encodedState); // twPew…

const loadCode = [
  'console.log("loaded i:", i);',
].join('\n');

function resumeFromState() {
  const state = Buffer.from(encodedState, 'base64');

  const loadScript = new vm.Script(loadCode, { cachedData: state });
  console.log('loadScript rejected?', loadScript.cachedDataRejected); // true

  const emptyScript = new vm.Script('', { cachedData: state });
  console.log('emptyScript rejected?', emptyScript.cachedDataRejected); // true

  const initScript = new vm.Script(initCode, { cachedData: state });
  console.log('initScript rejected?', initScript.cachedDataRejected); // true
  const otherSandbox = {
    c: consLog,
    i: 23,
    f: function hello() { return 'Hello World!'; },
    g: initSandbox.f,
  };

  initScript.runInNewContext(otherSandbox);
  // f() inside: Hello World!
  // g() inside: 43

  console.log('otherSandbox:', otherSandbox);
  // { c: [Function: consLog], i: 24, f: [Function: hello], g: [Function: f] }

  console.log('another f() outside says:', otherSandbox.f()); // Hello World!
}

resumeFromState();