on

This page describes the on() function in zalo-bot-js, used to register listeners for SDK-normalized event types.

This is one of the main ways to write a bot with the event-listener API.

Function signature

on(event: BotEvent, callback: BotEventCallback): this

Supported events

• message
• text
• photo
• sticker
• command

Callback shape

The callback receives:

• message: Message
• metadata: { update: Update }

Example

bot.on("message", async (message, metadata) => {
  console.log("[message]", {
    updateId: metadata.update.updateId,
    chatId: message.chat.id,
    messageId: message.messageId,
    fromUserId: message.fromUser?.id,
    messageType: message.messageType,
    eventTypes: metadata.update.eventTypes,
    text: message.text ?? null,
    sticker: message.sticker ?? null,
    photoUrl: message.photoUrl ?? null,
  });
});

Practical notes

• on("message") is the broadest listener
• on("text") runs only when the message has text
• if you need regex matching, use onText

Next

• See onText for regex-based matching.
• See processUpdate to understand how SDK events are emitted.

Last updated: April 5, 2026