Krzysztof Żuraw

Pomodoro timer - breaks & localStorage

  • #javascript
  • #pomodoro technique

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 = entries
      (entry) => `
        <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.