Realm Shim

This folder contains a shim implementation of the Realm API Proposal.

Limitations

The current implementation has 3 main limitations:

All code evaluated inside a Realm runs in strict mode.
Direct eval is not supported.
let, global function declarations and any other feature that relies on new bindings in global contour are not preserved between difference invocations of eval, instead we create a new contour everytime.

Building the Shim

git clone https://github.com/Agoric/realms-shim.git
cd realms-shim
npm install
npm run shim:build

This will install the necessary dependencies and build the shim locally.

Playground

To open the playground example in your default browser:

npm run shim:build
open examples/simple.html

Usage

To use the shim in a webpage, build the shim, then:

  <script src="../dist/realm-shim.min.js"></script>
  <script>
    const r = new Realm();
    [...]
  </script>

To use the shim with node:

  const Realm = require('./realm-shim.min.js');
  const r = new Realm();
  [...]

You can also use the ES6 module version of the Realms shim in Node.js via the package esm. To do that, launch node with esm via the "require" option:

npm install esm
node -r esm main.js

And import the realm module in your code:

  import Realm from './src/realm';
  const r = new Realm();
  [...]

Examples

Example 1: Root Realm

To create a root realm with a new global and a fresh set of intrinsics:

const r = new Realm(); // root realm
r.global === this; // false
r.global.JSON === JSON; // false

Example 2: Realm Compartment

To create a realm compartment with a new global and inherit the intrinsics from another realm:

const r1 = new Realm(); // root realm
const r2 = new r1.global.Realm({ intrinsics: 'inherit' }); // realm compartment
r1.global === r2.global; // false
r1.global.JSON === r2.global.JSON; // true

Example 3: Realm Compartment from current Realm

To create a realm compartment with a new global and inherit the intrinsics from the current execution context:

const r = new Realm({ intrinsics: 'inherit' }); // realm compartment
r.global === this; // false
r.global.JSON === JSON; // true

Bug Disclosure

Please help us practice coordinated security bug disclosure, by using the instructions in SECURITY.md to report security-sensitive bugs privately.

For non-security bugs, please use the regular Issues page.

AgoricBot/realms-shim