CommandHandler

This page describes CommandHandler in zalo-bot-js, a handler used to capture commands with syntax like /start.

CommandHandler is of the handler-based style and is often used with Application.

How it works

This Handler:

1. read update.message?.text
2. separate the first word by space
3. compare with /${command}
4. if matched, call callback with CallbackContext

For example

import "dotenv/config";
import { ApplicationBuilder, CommandHandler } from "zalo-bot-js";

const app = new ApplicationBuilder()
  .token(process.env.ZALO_BOT_TOKEN!)
  .build();

app.addHandler(new CommandHandler("start", async (update, ctx) => {
  await update.message?.replyText(`Xin chào ${ctx.args[0] ?? "bạn"}!`);
}));

void app.runPolling();

CallbackContext

In the callback, ctx.args contains the parameters after command.

Example with text:

/start abc

then ctx.args would be:

["abc"]

When should you use it?

• you want to catch the command explicitly with the syntax /name
• you are using Application instead of bot.onText()

Next

• See MessageHandler for processing by filter.
• See CallbackContext to understand received callback data.

Last updated: April 5, 2026