Middlewares
Dispatcher provides basic middleware functionality. It is not as extensible as middlewares in frameworks likes Telegraf, and that is by design, since we already have filters and propagation using which you can achieve pretty much the same.
Middlewares are only called for parsed updates.
Middleware types
Dispatcher supports 2 middlewares: pre-update and post-update.
Pre-update
Pre-update middleware is called right before an update is going to be dispatched, and can be used to skip that update altogether.
dp.onPreUpdate((upd) => {
// randomly skip 10% of updates
if (Math.random() < 0.1)
return PropagationAction.Stop
})dp.onPreUpdate((upd) => {
// randomly skip 10% of updates
if (Math.random() < 0.1)
return PropagationAction.Stop
})Post-update
Post-update middleware is called after an update was processed by the dispatcher. Whether the update was handled is also provided here:
dp.onPostUpdate((handled, upd) => {
if (handled) {
console.log(`handled ${upd.name}`)
}
})dp.onPostUpdate((handled, upd) => {
if (handled) {
console.log(`handled ${upd.name}`)
}
})Additional context
You can add some additional context in the pre-update middleware, and that context will also be available in post-update middleware and error handler:
interface TimerContext {
start: number
}
dp.onPreUpdate<TimerContext>((upd) => {
upd.start = Date.now()
})
dp.onPostUpdate<TimerContext>((handled, upd) => {
if (handled) {
console.log(`handled ${upd.name} in ${Date.now() - upd.start} ms`)
}
})
dp.onError<TimerContext>((err, upd) => {
console.log(`error for ${upd.name} after ${Date.now() - upd.start} ms`)
})interface TimerContext {
start: number
}
dp.onPreUpdate<TimerContext>((upd) => {
upd.start = Date.now()
})
dp.onPostUpdate<TimerContext>((handled, upd) => {
if (handled) {
console.log(`handled ${upd.name} in ${Date.now() - upd.start} ms`)
}
})
dp.onError<TimerContext>((err, upd) => {
console.log(`error for ${upd.name} after ${Date.now() - upd.start} ms`)
})Note that currently you can't access that context from handlers or filters (see mtcute#4).