import { type Middleware } from "https://deno.land/x/grammy@v1.29.0/mod.ts";
Middleware for grammY, either as a function or as a container for a function.
Simply put, middleware is just a fancy term for a listener. You can register middleware on a bot to listen for updates. Example:
bot.on('message', ctx => ctx.reply('I got your message!'))
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// ^
// |
// This is middleware!
Middleware receives one object that we call the context object. This is
another fancy term for a simple object that holds information about the
update you're processing. For instance, the context object gives you access
to the message that was sent to your bot (ctx.message
), including the text
(or photo or whatever message the user has sent). The context object is
commonly named ctx
.
It also provides you with the ctx.api
object that you also find on
bot.api
. As a result, you can call ctx.api.sendMessage
instead of
bot.api.sendMessage
. This prevents you from having to pass around your
bot
instance all over your code.
Most importantly, the context object gives you a handful of really useful
shortcuts, such as a reply
method (see above). This method is nothing else
than a wrapper around ctx.api.sendMessage
—but with some arguments
pre-filled for you. As you can see above, you no longer have to specify a
chat_id
or anything; the context object knows which chat it belongs to, so
when you call reply
, the context will call sendMessage
with the correct
chat_id
, namely the one for the same chat that the incoming message
originates from. This makes it very convenient to reply to a message.
Middleware is an extremely powerful concept and this short explanation only scratched the surface of what is possible with grammY. If you want to know more advanced things about middleware, check out the documentation on the website.