Find elapsed time in javascript

Question

I'm new to JavaScript and I'm trying to write a code which calculates the time elapsed from the time a user logged in to the current time.

Here is my code:-

function markPresent() {
    window.markDate = new Date();
    $(document).ready(function() {
        $("div.absent").toggleClass("present");
    });
    updateClock();
}

function updateClock() {    
    var markMinutes = markDate.getMinutes();
    var markSeconds = markDate.getSeconds();

    var currDate = new Date();
    var currMinutes = currDate.getMinutes();
    var currSeconds = currDate.getSeconds();
    var minutes = currMinutes - markMinutes;
    if(minutes < 0) { minutes += 60; }
    var seconds = currSeconds - markSeconds;
    if(seconds < 0) { seconds += 60; }

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

    var hours = 0;
    if(minutes == 59 && seconds == 59) { hours++; }
    if(hours < 10) { hours = "0" + hours; }

    var timeElapsed = hours+':'+minutes+':'+seconds;
    document.getElementById("timer").innerHTML = timeElapsed;
    setTimeout(function() {updateClock()}, 1000);
}

The output is correct upto 00:59:59 but after that that O/P is:

00:59:59 01:59:59 01:59:00 01:59:01 . . . . 01:59:59 01:00:00

How can I solve this and is there a more efficient way I can do this? Thank you.

Answer 1

No offence, but this is massively over-enginered. Simply store the start time when the script first runs, then subtract that from the current time every time your timer fires.

There are plenty of tutorials on converting ms into a readable timestamp, so that doesn't need to be covered here.

    var start = Date.now();
    
    setInterval(function() {
      document.getElementById('difference').innerHTML = Date.now() - start;
    
      // the difference will be in ms
    }, 1000);

<div id="difference"></div>

Answer 2

There's too much going on here.

An easier way would just be to compare markDate to the current date each time and reformat.

See Demo: http://jsfiddle.net/7e4psrzu/

function markPresent() {
    window.markDate = new Date();
    $(document).ready(function() {
        $("div.absent").toggleClass("present");
    });
    updateClock();
}

function updateClock() {  
    var currDate = new Date();
    var diff = currDate - markDate;
    document.getElementById("timer").innerHTML = format(diff/1000);
    setTimeout(function() {updateClock()}, 1000);
}

function format(seconds)
{
var numhours = parseInt(Math.floor(((seconds % 31536000) % 86400) / 3600),10);
var numminutes = parseInt(Math.floor((((seconds % 31536000) % 86400) % 3600) / 60),10);
var numseconds = parseInt((((seconds % 31536000) % 86400) % 3600) % 60,10);
    return ((numhours<10) ? "0" + numhours : numhours)
    + ":" + ((numminutes<10) ? "0" + numminutes : numminutes)
    + ":" + ((numseconds<10) ? "0" + numseconds : numseconds);
}

markPresent();

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script>
<div id="timer"></div>