How to use the @xviz/io.isEnvelope function in @xviz/io

processMessage(parsed) {
    if (isEnvelope(parsed)) {
      const unpacked = unpackEnvelope(parsed);

      if (unpacked.namespace === 'xviz') {
        this.callMiddleware(unpacked.type, unpacked.data);
      } else if (!this.unknownMessageTypes.has(parsed.type)) {
        // Report each unknown type just once
        this.unknownMessageTypes.add(parsed.type);
        console.log(`Unknown message namespace: "${unpacked.namespace}" type: "${unpacked.type}"`);
      }
    } else {
      console.log('Unknown message format', parsed);
    }
  }
  sendMessage(msgType, data) {