Potential Bug in DigitalWatch Sample Project: Date Update Issue on Sundays

Original Created Mar 08, 2017 | Regeneration Apr 22, 2026

Question

The DigitalWatch sample project contains a date update function that behaves differently when the application starts on Sunday (day 0) compared to other days. Here's the problematic code:

function updateDate(prevDay) {
    var datetime = tizen.time.getCurrentDateTime(),
        nextInterval,
        strDay = document.getElementById("str-day"),
        strFullDate,
        getDay = datetime.getDay(),
        getDate = datetime.getDate(),
        getMonth = datetime.getMonth();

    if (prevDay !== null) {
        if (prevDay === getDay) {
            nextInterval = 1000;
        } else {
            nextInterval = (23 - datetime.getHours()) * 60 * 60 * 1000 +
                         (59 - datetime.getMinutes()) * 60 * 1000 +
                         (59 - datetime.getSeconds()) * 1000 +
                         (1000 - datetime.getMilliseconds()) + 1;
        }
    }

    if (getDate < 10) {
        getDate = "0" + getDate;
    }

    strFullDate = arrDay[getDay] + " " + getDate + " " + arrMonth[getMonth];
    strDay.innerHTML = strFullDate;

    if (timerUpdateDate) {
        clearTimeout(timerUpdateDate);
    }

    timerUpdateDate = setTimeout(function() {
        updateDate(getDay);
    }, nextInterval);
}

The issue occurs because:

When the method is first called with parameter 0 (Sunday), it sets a 1-second interval for updates
On other days (1-6), it correctly calculates the time until midnight
This causes the function to be called every second all day when started on Sunday

A temporary fix was found by changing the initial parameter to -1, but this doesn't seem like the intended behavior.

Answer

Problem Understanding

The issue stems from how JavaScript handles the prevDay parameter in the date update logic. When:

prevDay is 0 (Sunday) and getDay() returns 0, the function sets a 1-second interval
This differs from the intended behavior where it should calculate the time until midnight

Solution Methods

Parameter Check Modification:
- Change the initial parameter from 0 to null or undefined
- Modify the condition to handle falsy values properly
Code Restructuring:
- Move the date update logic into the main time update function
- Avoid separate setTimeout calls for date updates

Code Examples

Here's an improved version:

function updateDateTime() {
    var datetime = tizen.time.getCurrentDateTime();
    var currentDay = datetime.getDay();
    
    // Update time display
    // ... existing time update code ...
    
    // Update date display if day changed
    if (typeof lastDay === 'undefined' || lastDay !== currentDay) {
        var getDate = datetime.getDate();
        if (getDate < 10) getDate = "0" + getDate;
        
        var strFullDate = arrDay[currentDay] + " " + getDate + " " + arrMonth[datetime.getMonth()];
        document.getElementById("str-day").innerHTML = strFullDate;
        lastDay = currentDay;
    }
    
    // Schedule next update
    timerUpdate = setTimeout(updateDateTime, 1000);
}

Additional Tips

Consider using Date object methods directly instead of Tizen's time API for simpler date handling
For production code, implement proper error handling around time API calls
Test thoroughly across different time zones and daylight saving transitions