decodeString(str) {
        let i = 0;
        // look up type
        const p = {
            type: Number(str.charAt(0)),
        };
        if (PacketType[p.type] === undefined) {
            throw new Error("unknown packet type " + p.type);
        }
        // look up attachments if type binary
        if (p.type === PacketType.BINARY_EVENT ||
            p.type === PacketType.BINARY_ACK) {
            const start = i + 1;
            while (str.charAt(++i) !== "-" && i != str.length) { }
            const buf = str.substring(start, i);
            if (buf != Number(buf) || str.charAt(i) !== "-") {
                throw new Error("Illegal attachments");
            }
            p.attachments = Number(buf);
        }
        // look up namespace (if any)
        if ("/" === str.charAt(i + 1)) {
            const start = i + 1;
            while (++i) {
                const c = str.charAt(i);
                if ("," === c)
                    break;
                if (i === str.length)
                    break;
            }
            p.nsp = str.substring(start, i);
        }
        else {
            p.nsp = "/";
        }
        // look up id
        const next = str.charAt(i + 1);
        if ("" !== next && Number(next) == next) {
            const start = i + 1;
            while (++i) {
                const c = str.charAt(i);
                if (null == c || Number(c) != c) {
                    --i;
                    break;
                }
                if (i === str.length)
                    break;
            }
            p.id = Number(str.substring(start, i + 1));
        }
        // look up json data
        if (str.charAt(++i)) {
            const payload = this.tryParse(str.substr(i));
            if (Decoder.isPayloadValid(p.type, payload)) {
                p.data = payload;
            }
            else {
                throw new Error("invalid payload");
            }
        }
        return p;
    }
Decode a packet String (JSON data)

@param {String} str
@return {Object} packet