cannot read property startswith of undefined
Your issue is, that you mix discord.js with discord.io
discord.js is object oriented where discord.io is not, so in discord.io your message is already a string!
Example discord.io message event.
bot.on('message', function(user, userID, channelID, message, event) {
if (message === "ping") {
bot.sendMessage({
to: channelID,
message: "pong"
});
}
});