Handling Updates

You can handle updates by assigning update handlers to the client. A handler is a function that takes two arguments: ctx and next.

ctx is the received update with context-aware methods and shortcuts. See all types of updates here.

next is a function that passes the update to the next handlers.

Once an update reaches a handler, it won’t reach others unless it calls next. When next is called, the same thing goes on again: the update won’t reach the next handler until next is called, and so on.

There are four methods responsible for assigning handlers:

• use
• branch
• filter
• on

use

This is the main method to assign a handler, and all others depend on it. It assigns an unconditional handler, meaning that it will always get called unless it is blocked by a handler preceding it.

|
use———————handler
           |
           |
           |
         next
          /
         /
        /
       /
      /
     /
    /
   /
  /
 /
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The following are some usage examples.

/** Logging */
client.use(async (ctx, next) => {
  console.log("I always get logged before an update is handled.");
  console.log("Update", ctx.toJSON(), "received at", Date.now());
  await next(); // move to the next handlers
});

/** Error handling */
client.use(async (_ctx, next) => {
  try {
    await next(); // call the next handlers
  } catch (err) {
    console.error("Failed to handle an update:");
    console.trace(err);
  }
});

/** Ignoring updates */
client.use(async (ctx, next) => {
  const message = ctx.effectiveMessage;
  const date = message?.date;
  const isTooOld = date !== undefined && Date.now() - date.getTime() > 5 * 60 * 1_000;
  if (message !== undefined && isTooOld) {
    // message is older than 5 minutes, not interesting
    console.log(
      "Ignoring messsage", message.id,
      "in", message.chat.id,
      "because it is too old.",
    );
  } else {
    await next(); // handle it if newer than 5 minutes
  }
});

/** Performance monitoring */
client.use(async (_ctx, next) => {
  const then = performance.now();
  await next(); // call the next handlers
  const elapsed = performance.now() - then;
  console.log("Update handled in", ${Math.round(elapsed)}ms`);
});

branch

branch takes 3 functions:

1. One that checks for a specific condition.
2. A handler function that gets called when the specific condition is met, the true handler.
3. Another one that gets called when it is not met, the false handler.

|
branch————————
              |
          condition
              |
         ————————————
        |            |
      true         false
        |            |
     handler      handler
        |            |
      next         next
       /            /
      /            /
     /            /
    /            /
   /            /
  /            /
 /            /
|            /
|           /
|          /
|         /
|        /
|       /
|      /
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|    /
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| /
|/
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Here’s an example.

client.branch(
  /** condition: update is from a special user */
  (ctx) => ctx.effectiveUser?.username?.toLowerCase() == "onetimeusername",
  /** true handler */
  () => {
    console.log("Using more compute power: Update from someone special.");
  },
  /** false handler */
  () => {
    console.log("Handling postponed: Update from regular user.");
  },
);

filter

filter is almost the same as branch except that it does not have a false handler. It automatically moves to the next handlers if the condition is not met.

|
filter————————
              |
          condition
              |
         ————————————
        |            |
      true         false
        |           /
     handler       /
        |         /
      next       /
       /        /
      /        /
     /        /
    /        /
   /        /
  /        /
 /        /
|        /
|       /
|      /
|     /
|    /
|   /
|  /
| /
|/
|

Here’s an example.

client.filter(
  /** condition: update is from a forum chat */
  (ctx) => {
    return ctx.effectiveChat?.type == "supergroup" && ctx.effectiveChat.isForum;
  },
  (ctx) => {
    console.log("Received an update from a forum.");
  },
);

on

on works like filter but instead of providing a function that checks for a condition, you provide it a filter query. If the update matched the provided filter, the handler gets called.

|
on————————————
              |
            check
              |
         ————————————
        |            |
     passes      does not
        |           /
     handler       /
        |         /
      next       /
       /        /
      /        /
     /        /
    /        /
   /        /
  /        /
 /        /
|        /
|       /
|      /
|     /
|    /
|   /
|  /
| /
|/
|

Here are some examples.

/** When the client's connection state changes */
client.on("connectionState", ({ connectionState }) => {
  console.log("New connection state:", connectionState);
});

/** Handles text messages */
client.on("message:text", ({ message }) => {
  // do something with message.text
});

/** Handles callback queries */
client.on("callbackQuery", ({ callbackQuery }) => {
  // do something with callbackQuery
});