# React Chrono: Start/Pause & Stop

> Build a simple chronometer in React with two buttons: Start/Pause (toggle) and Stop (reset).

- Difficulty: beginner
- Tags: useState
- Estimated time: 45 minutes
- Tests: 5
- Requires subscription: no

## Overview

Build a simple chronometer in React with two buttons: Start/Pause (toggle) and Stop (reset).


## Requirements

- Display the timer starting at `00:00.0`.
- Toggle the timer with a **Start/Pause** button:
  - Start counting when pressed.
  - Pause counting when pressed again.
- Reset the timer to `00:00.0` with a **Stop** button.
- Update the timer display in tenths of a second while running.
- Ensure that multiple presses of Start/Pause behave correctly (do not create multiple intervals).
- Make the buttons accessible with proper `aria-label`s (Play, Pause, Stop)


## Notes

- Use `setInterval` and `clearInterval` to control the timer.
- Consider storing the interval ID in state or a ref to manage starting and stopping correctly.
- Formatting the timer into minutes, seconds, and tenths can be done with helper functions.
- Tests check the buttons’ aria-labels, so make sure to add them.


## Tests

01. renders the timer at 00:00.0 initially
02. starts counting when Play is pressed
03. pauses when Pause is pressed
04. can resume after pausing
05. resets to 00:00.0 when Stop is pressed