RegExp converting military time JavaScript

Question

I am trying to convert military time from a string with regex... what I have so far is

var a = "[18:37:56]";
var b = a.replace(/(\[|\])/g,'');
var c = b.match(/^[0-9][0-9]/);
var d = Number(c[0]) > 12 ? Number(c[0]) - 12 : Number(c[0]);
b.replace(/^[0-9][0-9]/,d);

The first replace is to get rid of the square brackets. Then we match the first two numbers, then after this we will see if that number is greater than 12, if so subtract 12 if not leave it alone. Then replace those numbers with the corresponding number.

Problem is for one, what if the for c there is no second number, meaning it's only at 12:01am or 9:59am in standard time. I'm seeing a lot of flaws that can come up with this, does anyone have any better solutions than what I've done?

Can you explain modulo is that with Vanilla JS? and what is the % for in terms of here. — EasyBB
– EasyBB, Commented Feb 18, 2014 at 23:58
change var c = b.match(/^[0-9]{1,2}/); to handle the single number issue — Will P.
– Will P., Commented Feb 19, 2014 at 0:00
The modulo operator gives you the remainder of a division. It's useful for many things, like figuring out if a number is odd or even, do something every nth iteration, etc... — elclanrs
– elclanrs, Commented Feb 19, 2014 at 0:05

Niet the Dark Absol · Accepted Answer · 2014-02-19 00:01:30Z

3

One-liner:

alert("[18:37:56]".substr(1,8).replace(/^\d\d?/,function(m) {return (m%12)||12;}));

If you want to append am or pm:

"[18:37:56]".replace(/\[(\d\d?)(:\d\d:\d\d)\]/,function(_,h,ms) {return ((h%12)||12)+ms+(h>=12?"p":"a")+"m";});

answered Feb 19, 2014 at 0:01

Niet the Dark Absol

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7 Comments

EasyBB Over a year ago

This looks nice and simple, though the issue arrises again with the substring as it won't always have 8 characters ;)

Niet the Dark Absol Over a year ago

See edit - the second code does everything at once and allows for the single-digit case (although usually military time has a leading zero anyway)

EasyBB Over a year ago

Ok let me see how this chat works, I'm going to change my time on my computer (if that is what it's going by) and see if their is a leading zero) if not whatever ;)

EasyBB Over a year ago

I took it off. Realized just now that I clicked it when reading.

EasyBB Over a year ago

@NiettheDarkAbsol why is your regex looking through the minutes and seconds? Just curious mate

|

Bart · Accepted Answer · 2014-02-19 00:05:01Z

0

You should probably just use dates...

var time = "[18:37:56]";
var date = new Date("1 january 2014 " + time.substring(1, time.length - 1));

date.getHours() % 12 == 6
date.getMinutes() == 37
date.getSeconds() == 56

By the way, dates do need day/month/year, but since every day has the same number of hours, you can enter any date you want. It's the hours, minutes and seconds that matter.

answered Feb 19, 2014 at 0:05

Bart

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5 Comments

EasyBB Over a year ago

This is for a chat functionality that is already implemented on our forum sites. We don't have access to the php so I do these little JS 'hacks'. I don't think this would be very useful in the long run.

Bart Over a year ago

This is javascript... Javascript has a Date type.

EasyBB Over a year ago

HAHA I know this, I'm saying the implementation of this isn't very plausible unless it's going off my time or PHP time frame.

Bart Over a year ago

I... don't see what php time has to do with this. You just take the time string "[18:37:56]" as you got it in your original post, and you extract the hours, minutes and seconds from it?

EasyBB Over a year ago

Oh ok I see what your doing. Your using the string as the input of the new date then modular it for the hours. ;) I thought you were using the gethours for the hours. That's a big Simpson D'oh :D lol my bad

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