class ShadowRealm | globals module | Bun

ShadowRealms are a distinct global environment, with its own global object containing its own intrinsics and built-ins (standard objects that are not bound to global variables, like the initial value of Object.prototype).

const red = new ShadowRealm();

// realms can import modules that will execute within it's own environment.
// When the module is resolved, it captured the binding value, or creates a new
// wrapped function that is connected to the callable binding.
const redAdd = await red.importValue('./inside-code.js', 'add');

// redAdd is a wrapped function exotic object that chains it's call to the
// respective imported binding.
let result = redAdd(2, 3);

console.assert(result === 5); // yields true

// The evaluate method can provide quick code evaluation within the constructed
// shadowRealm without requiring any module loading, while it still requires CSP
// relaxing.
globalThis.someValue = 1;
red.evaluate('globalThis.someValue = 2'); // Affects only the ShadowRealm's global
console.assert(globalThis.someValue === 1);

// The wrapped functions can also wrap other functions the other way around.
const setUniqueValue =
await red.importValue('./inside-code.js', 'setUniqueValue');

// setUniqueValue = (cb) => (cb(globalThis.someValue) * 2);

result = setUniqueValue((x) => x ** 3);

console.assert(result === 16); // yields true

Creates a new ShadowRealm

const red = new ShadowRealm();

// realms can import modules that will execute within it's own environment.
// When the module is resolved, it captured the binding value, or creates a new
// wrapped function that is connected to the callable binding.
const redAdd = await red.importValue('./inside-code.js', 'add');

// redAdd is a wrapped function exotic object that chains it's call to the
// respective imported binding.
let result = redAdd(2, 3);

console.assert(result === 5); // yields true

// The evaluate method can provide quick code evaluation within the constructed
// shadowRealm without requiring any module loading, while it still requires CSP
// relaxing.
globalThis.someValue = 1;
red.evaluate('globalThis.someValue = 2'); // Affects only the ShadowRealm's global
console.assert(globalThis.someValue === 1);

// The wrapped functions can also wrap other functions the other way around.
const setUniqueValue =
await red.importValue('./inside-code.js', 'setUniqueValue');

// setUniqueValue = (cb) => (cb(globalThis.someValue) * 2);

result = setUniqueValue((x) => x ** 3);

console.assert(result === 16); // yields true