function shouldIncludeBinaryHeader(packet, encoded) {
    // 48 === "0".charCodeAt(0) (OPEN packet type)
    // 54 === "6".charCodeAt(0) (NOOP packet type)
    return packet.type === "message" && typeof packet.data !== "string" && encoded[0] >= 48 && encoded[0] <= 54;
  }
Feature detection for WebSocket.

@return {Boolean} whether this transport is available.
@private