Does chrome extension internally use JSON.stiringify to postMessage over to background page?

Question

A message can contain any valid JSON object (null, boolean, number, string, array, or object)

The chrome extension specification indicat

Answer 1

The messages are automatically JSON-serialized (literally using JSON.stringify) in Chrome's JavaScript shim layer that interacts with an extension as can be seen in the source code of messaging.js:

  PortImpl.prototype.postMessage = function(msg) {
    if (!$Object.hasOwnProperty(ports, this.portId_))
      throw new Error(kPortClosedError);

    // JSON.stringify doesn't support a root object which is undefined.
    if (msg === undefined)
      msg = null;
    msg = $JSON.stringify(msg);
    if (msg === undefined) {
      // JSON.stringify can fail with unserializable objects. Log an error and
      // drop the message.
      //
      // TODO(kalman/mpcomplete): it would be better to do the same validation
      // here that we do for runtime.sendMessage (and variants), i.e. throw an
      // schema validation Error, but just maintain the old behaviour until
      // there's a good reason not to (http://crbug.com/263077).
      console.error('Illegal argument to Port.postMessage');
      return;
    }
    messagingNatives.PostMessage(this.portId_, msg);
  };

Ditto for JSON.parse:

  // Called by native code when a message has been sent to the given port.
  function dispatchOnMessage(msg, portId) {
    var port = ports[portId];
    if (port) {
      if (msg)
        msg = $JSON.parse(msg);
      port.onMessage.dispatch(msg, port);
    }
  };

N.B. chrome.runtime.postMessage/sendMessage is just a wrapper over PortImpl shown above.