This app lets you adjust the length of the pomodoro (work timer) and break timer, and an alarm will sound when the time has elapsed.
To show the elapsed time visually, a blue circle will be drawn inside of the black circle as the pomodoro counts down, and once completed, the blue circle will be erased as the break timer counts down. This was done using the html canvas element to draw a percentage of the circle based on how much time had elapsed relative to the initial time.
Check it out on codepen here.