Cross your first boundary.

1. Install and import

npm install js-message

import Message from 'js-message';

Version 3.1.1 keeps one native JavaScript implementation. Node 22.13+ can load it through import or synchronous require(), with no runtime dependency or compile step.

Native browser ESM

<script type="importmap">
{
  "imports": {
    "js-message": "./node_modules/js-message/index.js",
    "js-message/": "./node_modules/js-message/"
  }
}
</script>
<script type="module">
  import Message from 'js-message';

  console.log(new Message({ type: 'page.ready' }).JSON);
</script>

The map is complete because js-message has zero runtime dependencies, so no dependency or scope entries are needed. Its paths are relative to the HTML document. Serve the app over HTTP(S), and configure the server to expose these node_modules files; file:// is not supported.

2. Create and serialize

const message = new Message();

message.type = 'order.created';
message.data = {
    id: 'ord_481',
    total: 27.50
};

transport.send(message.JSON);

message.JSON is a string containing only type and data. Other properties you add to the instance stay local.

3. Load and branch

const incoming = new Message();
incoming.load(receivedValue);

if (incoming.type === 'error') {
    console.error(incoming.data.err);
} else {
    route(incoming.type, incoming.data);
}

load() accepts a JSON string or an existing object and copies the fields that are available. Malformed or uncoercible input becomes a recoverable type: 'error' message instead of escaping from load().