node_modules/engine.io-parser/build/esm/commons.js

const PACKET_TYPES = Object.create(null); // no Map = no polyfill
PACKET_TYPES["open"] = "0";
PACKET_TYPES["close"] = "1";
PACKET_TYPES["ping"] = "2";
PACKET_TYPES["pong"] = "3";
PACKET_TYPES["message"] = "4";
PACKET_TYPES["upgrade"] = "5";
PACKET_TYPES["noop"] = "6";
const PACKET_TYPES_REVERSE = Object.create(null);
Object.keys(PACKET_TYPES).forEach(key => {
    PACKET_TYPES_REVERSE[PACKET_TYPES[key]] = key;
});
const ERROR_PACKET = { type: "error", data: "parser error" };
export { PACKET_TYPES, PACKET_TYPES_REVERSE, ERROR_PACKET };