Categories

# How to the Number of Seconds to a Time String in the hh:mm:ss Format with JavaScript?

Sometimes, we may want to convert the number of seconds elapsed to a time string in the hh:mm:ss format in our JavaScript app.

In this article, we’ll look at how to convert the number of seconds to a time string in hh:mm:ss format.

### Create Our Own Function

We can create our own function to convert the number of seconds elapsed to a time string in hh:mm:ss format.

For instance, we can write:

const toHHMMSS = (numSecs) => {
let secNum = parseInt(numSecs, 10);
let hours = Math.floor(secNum / 3600).toString().padStart(2, '0');
let minutes = Math.floor((secNum - (hours * 3600)) / 60).toString().padStart(2, '0');;
let seconds = secNum - (hours * 3600) - (minutes * 60).toString().padStart(2, '0');;
return `\${hours}:\${minutes}:\${seconds}`;
}

console.log(toHHMMSS(1234))

In the toHHMMSS function, we parse the numSecs parameter into a number.

Then we compute the hours by dividing secNum by 3600.

Then we round it down to the nearest integer with Math.floor .

Then we call toString on it to convert it into a string.

And then we call padStart to pad the number string to 2 digits with a leading zero if necessary.

To compute the minutes , we subtract secNum by the hours multiplied by 3600 and divide the whole thing by 60.

We get the minutes after subtracting the hours.

And we round the number down to the nearest integer with Math.floor .

Then we pad it into a 2 digit string with padStart also.

Next, we compute the seconds by subtracting the hours and minutes converted to seconds from secNum .

Then we convert it to a string and call padStart on it to pad the string to 2 digits with a leading zero if necessary.

And finally, we return the hours , minutes , and seconds in a string.

Therefore, the console log should log:

'00:20:34'

### Date.prototype.toISOString

We can call toISOString on the JavaScript date object to get a date string with the hours, minutes, and seconds.

To get the elapsed time, we just create a date with timestamp 0, then call setSeconds to set the timestamp to the elapsed seconds.

And then we can all toISOString to get the date string and extract the hours, minutes, and seconds part of the returned date string.

For instance, we can write:

const date = new Date(0);
date.setSeconds(1234);
const timeString = date.toISOString().substr(11, 8);
console.log(timeString)

We create a Date instance with timestamp 0.

Then we call setSeconds to set the seconds of the time.

And then we call toISOString to get a date string.

Then we call substr to extract the hours, minutes, and seconds substring.

Therefore, timeString is:

'00:20:34'

### Conclusion

We can use math, date, and string methods to get the elapsed seconds into hh:mm:ss format easily with JavaScript.

## By John Au-Yeung

Web developer specializing in React, Vue, and front end development.