💠Back Button

A component responsible for the Telegram Mini Apps back button. The button is supported since Mini Apps v6.1.

Checking Support

To check if the back button can be used, call the isSupported function. It returns true if the SDK is initialized and the Telegram client supports the back button.

import { backButton } from '@tma.js/sdk';

backButton.isSupported(); // boolean

Mounting

Before using the component, mount it with the mount method. If the page was reloaded, the component restores the state saved before the reload. The isMounted computed value reflects the current mount status.

backButton.mount();
backButton.isMounted(); // true

mount throws NotInitializedError if the SDK is not initialized, and MethodUnsupportedError if the back button is unsupported.

To unmount the component, use the unmount method:

backButton.unmount();
backButton.isMounted(); // false

Showing and Hiding

To change the button visibility, use the show and hide methods. They update the isVisible computed value.

backButton.show();
backButton.isVisible(); // true

backButton.hide();
backButton.isVisible(); // false

Both methods throw:

• NotInitializedError if the SDK is not initialized;
• MethodUnsupportedError if the back button is unsupported;
• NotMountedError if the component is not mounted.

Tracking Clicks

To add a click listener, use the onClick method. It returns a function removing the listener. Alternatively, use the offClick method.

function listener() {
  console.log('Clicked!');
}

const offClick = backButton.onClick(listener);
offClick();
// or
backButton.onClick(listener);
backButton.offClick(listener);

The second argument is an optional object with the following properties:

• once?: boolean: remove the listener after the first call;
• signal?: AbortSignal: remove the listener when the signal is aborted.

const controller = new AbortController();

backButton.onClick(listener, { once: true, signal: controller.signal });
controller.abort();

onClick and offClick never throw, and they don't require the component to be mounted.

State

The component state is available via the state computed value. Like other computed values, it can be subscribed to.

backButton.state(); // { isVisible: false }

const unsubscribe = backButton.isVisible.subscribe((next, prev) => {
  console.log('isVisible changed:', prev, '->', next);
});
unsubscribe();