Krzysztof Żuraw blog

Pomodoro timer - breaks & localStorage

March 05, 2017

Hello! In today blog post I will write what I learn during this week of pomodoro timer development - breaks and localStorage.

Breaks for pomodoro timer

The whole idea of pomodoro is that after every 25 minutes of work you have 5 minutes of break to get up from computer and rest. I wanted to implement the same in my timer.

As I already have function timer to which I pass number of seconds to countdown, all I need to do is to figure out when to call timer(300) for 5 minutes break.

I did this by passing flag to timer called hasBreakAfter - if timer has break after call timer with 300 seconds if not go on with the flow.

function timer(seconds, hasBreakAfter = true){
  // function body
  if (secondsLeft < 0){

function makeBreak(hasBreak) {
  if (hasBreak) {
    timer(300, false);

I also have to adjust notifications text:

// inside if in timer function
displayNotification(hasBreakAfter ? 'Time to rest dude!' : 'Time to work dude!');

Displaying & storing breaks and pomodoros

I have my breaks and pomodoros but it will be awesome to present it to the user so he can see how much time he works today.

After notification is displayed I use saveTimeEntryToLocalStorage:

const entries = JSON.parse(localStorage.getItem('entries')) || [];

function extractHoursMinutes(date) {
  return date.split(' ').splice(4, 1)[0].slice(0, 5);

function saveTimeEntryToLocalStorage(startSeconds, endSeconds, type) {
  const startTime = extractHoursMinutes(Date(startSeconds));
  const endTime = extractHoursMinutes(Date(endSeconds));

  const entry = {
  localStorage.setItem('entries', JSON.stringify(entries));

To this function I pass: when given entry starts, end and what type it was. First thing is to extract hours:minutes from JavaScript Date. I do this in extractHoursMinutes by some play with arrays and strings.

JavaScript Date returns full date:"Sun Mar 05 2017 11:59:19 GMT+0100 (CET)". I split this string by whitespace then I take the fourth element which is hours:minutes:seconds and returns only hours:minutes.

I have my start and end time ready I can create entry object which then I add to entries. entries are JavaScript list of objects from localStorage. If nothing is currently in localStorage list is empty. At the end I store updated entries in localStorage by localStorage.setItem().

The last thing is to get these entries and render them to the end user:

function retrieveTimeEntryFromLocalStorage() {
  tableBody.innerHTML = => `
        <td class="mdl-data-table__cell--non-numeric">${entry.startTime}</td>
        <td class="mdl-data-table__cell--non-numeric">${entry.endTime}</td>
        <td class="mdl-data-table__cell--non-numeric">${entry.type}</td>

Here is iterate over entries and take every one of them add to respective td and save to HTML. Be sure that you spell HTML in innerHTML capitalised as I was debugging this error for quite a time.

One more thing is to reset and clear localStorage:

resetLocalStorageBtn.addEventListener('click', () => {

I also reload page without cache by window.location.reload(true).

Entries look as follows:


That’s all for today! Feel free to comment - I really appreciate that. In the next week, I will try to implement good and bad pomodoros.

Repo with this code is available on github.

Want to get blog posts via email?

Powered by Buttondown.

Krzysztof Żuraw

Written by Krzysztof Żuraw who lives and works in Wrocław. You can find more on about page and subscribe to rss feed.