Develop Reference

Store Hours: Display Current Time and Holidays

So, I'm working to add store hours to a particular site. I found this great bit of JS that displays the current time when the page loads and identifies whether or not the store is closed. However, I would like to change the time captured at time of page loading to an active clock. I'm hoping someone can assist.
When the page loads, it displays the time at which the page loads. i.e. Visit site at 12:30PM, timeDiv displays 12:30PM. At 12:31PM, it still displays 12:30PM.
What I would like instead is an active clock, so that at 12:31PM it displays 12:31PM and displays the current time at each interval after that.
Here's the link to the original Pen: https://codepen.io/zeinab92/pen/xwWGWM
var now = new Date();
var weekday = new Array(7);
weekday[0] = "Sunday";
weekday[1] = "Monday";
weekday[2] = "Tuesday";
weekday[3] = "Wednesday";
weekday[4] = "Thursday";
weekday[5] = "Friday";
weekday[6] = "Saturday";
var checkTime = function() {
var today = weekday[now.getDay()];
var timeDiv = document.getElementById('timeDiv');
var dayOfWeek = now.getDay();
var hour = now.getHours();
var minutes = now.getMinutes();
//add AM or PM
var suffix = hour >= 12 ? "PM" : "AM";
// add 0 to one digit minutes
if (minutes < 10) {
minutes = "0" + minutes; }
if ((dayOfWeek === 1 || dayOfWeek === 2 || dayOfWeek === 3 || dayOfWeek === 4 || dayOfWeek === 5) && hour >= 9 && hour === 17 && minutes <=29) {
hour = ((hour + 11) % 12 + 1); //i.e. show 1:15 instead of 13:15
timeDiv.innerHTML = 'it\'s ' + today + ' ' + hour + ':' + minutes + suffix + ' - we\'re open!';
timeDiv.className = 'open';
}
else if ((dayOfWeek === 6) && hour >= 8 && hour === 15 && minutes <= 59) {
hour = ((hour + 11) % 12 + 1);
timeDiv.innerHTML = '<p id="hour">it\'s ' + today + ' ' + hour + ':' + minutes + suffix + '</p> <p id="stat">we\'re open!</p>';
timeDiv.className = 'open';
}
else {
if (hour === 0 || hour > 12) {
hour = ((hour + 11) % 12 + 1); //i.e. show 1:15 instead of 13:15
}
timeDiv.innerHTML = '<p id="hour">It\'s ' + today + ' ' + hour + ':' + minutes + suffix + '</p><p id="stat">we\'re closed!</>';
timeDiv.className = 'closed';
}
};
var currentDay = weekday[now.getDay()];
var currentDayID = "#" + currentDay; //gets todays weekday and turns it into id
$(currentDayID).toggleClass("today"); /hightlights today in the view hours modal popup
setInterval(checkTime, 1000);
checkTime();

There is a very popular library for JavaScript called momentjs and it handles a lot of date/time logic nicely. I'd recommend you start there.
This code extends momentjs in much the same way you'd need to put into your holidays:
https://gist.github.com/jrhames/5200024
The basic logic is to track your holidays in a separate custom array then create a function that takes a date as a parameter and does a lookup into your array of holidays.

How to set Am and Pm for Clock [duplicate]

I have buttons with the names of big cities.
Clicking them, I want to get local time in them.
$('#btnToronto').click(function () {
var hours = new Date().getHours();
var hours = hours-2; //this is the distance from my local time
alert ('Toronto time: ' + hours + ' h'); //this works correctly
});
But how can I get AM or PM ?

You should just be able to check if hours is greater than 12.
var ampm = (hours >= 12) ? "PM" : "AM";
But have you considered the case where the hour is less than 2 before you subtract 2? You'd end up with a negative number for your hour.

Try below code:
$('#btnToronto').click(function () {
var hours = new Date().getHours();
var hours = (hours+24-2)%24;
var mid='am';
if(hours==0){ //At 00 hours we need to show 12 am
hours=12;
}
else if(hours>12)
{
hours=hours%12;
mid='pm';
}
alert ('Toronto time: ' + hours + mid);
});

You can use like this,
var dt = new Date();
var h = dt.getHours(), m = dt.getMinutes();
var _time = (h > 12) ? (h-12 + ':' + m +' PM') : (h + ':' + m +' AM');
Hopes this will be better with minutes too.

const now = new Date()
.toLocaleTimeString([], { hour: '2-digit', minute: '2-digit', hour12: true })
.toLowerCase();
Basically you just need to put {hour12: true} and it's done.
result => now = "21:00 pm";

If hours is less than 12, it's the a.m..
var hours = new Date().getHours(), // this is local hours, may want getUTCHours()
am;
// adjust for timezone
hours = (hours + 24 - 2) % 24;
// get am/pm
am = hours < 12 ? 'a.m.' : 'p.m.';
// convert to 12-hour style
hours = (hours % 12) || 12;
Now, for me as you didn't use getUTCHours, it is currently 2 hours after
hours + ' ' + am; // "6 p.m."

very interesting post. in a function that take a date in parameter it can appear like that :
function hourwithAMPM(dateInput) {
var d = new Date(dateInput);
var ampm = (d.getHours() >= 12) ? "PM" : "AM";
var hours = (d.getHours() >= 12) ? d.getHours()-12 : d.getHours();
return hours+' : '+d.getMinutes()+' '+ampm;
}

with date.js
<script type="text/javascript" src="http://www.datejs.com/build/date.js"></script>
you can write like this
new Date().toString("hh:mm tt")
cheet sheet is here format specifiers
tt is for AM/PM

Try this:
h = h > 12 ? h-12 +'PM' : h +'AM';

The best way without extensions and complex coding:
date.toLocaleString([], { hour12: true});
How do you display javascript datetime in 12 hour AM/PM format?

here is get time i use in my code
let current = new Date();
let cDate = current.getDate() + '-' + (current.getMonth() + 1) + '-' + current.getFullYear();
let hours = current.getHours();
let am_pm = (hours >= 12) ? "PM" : "AM";
if(hours >= 12){
hours -=12;
}
let cTime = hours + ":" + current.getMinutes() + ":" + current.getSeconds() +" "+ am_pm;
let dateTime = cDate + ' ' + cTime;
console.log(dateTime); // 1-3-2021 2:28:14 PM

var now = new Date();
var hours = now.getHours();
var minutes = now.getMinutes();
var ampm = hours >= 12 ? 'pm' : 'am';
hours = hours % 12;
hours = hours ? hours : 12;
minutes = minutes < 10 ? '0' + minutes : minutes;
var timewithampm = hours + ':' + minutes + ' ' + ampm;
return timewithampm;

var dt = new Date();
var h = dt.getHours(),
m = dt.getMinutes();
var time;
if (h == 12) {
time = h + ":" + m + " PM";
} else {
time = h > 12 ? h - 12 + ":" + m + " PM" : h + ":" + m + " AM";
}
//var time = h > 12 ? h - 12 + ":" + m + " PM" : h + ":" + m + " AM";
console.log(`CURRENT TIME IS ${time}`);
This will work for everytime,

function Timer() {
var dt = new Date()
if (dt.getHours() >= 12){
ampm = "PM";
} else {
ampm = "AM";
}
if (dt.getHours() < 10) {
hour = "0" + dt.getHours();
} else {
hour = dt.getHours();
}
if (dt.getMinutes() < 10) {
minute = "0" + dt.getMinutes();
} else {
minute = dt.getMinutes();
}
if (dt.getSeconds() < 10) {
second = "0" + dt.getSeconds();
} else {
second = dt.getSeconds();
}
if (dt.getHours() > 12) {
hour = dt.getHours() - 12;
} else {
hour = dt.getHours();
}
if (hour < 10) {
hour = "0" + hour;
} else {
hour = hour;
}
document.getElementById('time').innerHTML = hour + ":" + minute + ":" + second + " " + ampm;
setTimeout("Timer()", 1000);
}
Timer()
<div id="time"></div>

Jquery function to Increment one hours based on time input string

I have string value in this format.
9:00 am
i want it to be like this.
9:00 am - 10:00 am
second hour must be 1 greater then first one. for example if time is
7:00 am then it should be 7:00 am - 8:00 am
how can i do that using jquery?
i tried this but its not working as it works now.
var time= "9:00 am"
var nexttime=time.setHours(time.getHours()+1)
alert(nexttime);
getting error of
time.getHours is not a function

You can try this :
function increaseTimeByOne(timeStr) {
var splitedTimeStr = timeStr.split(':');
var hours = parseInt(splitedTimeStr[0]);
var meridiem = splitedTimeStr[1].split(" ")[1];
var minutes = splitedTimeStr[1].split(" ")[0];
var nextHours = (hours + 1);
var nextMeridiem;
if (hours >= 11) {
if (meridiem.toLowerCase() == "am") {
nextMeridiem = "pm";
} else if (meridiem.toLowerCase() == "pm") {
nextMeridiem = "am";
}
if (nextHours > 12) {
nextHours = nextHours - 12;
}
} else {
nextMeridiem = meridiem;
}
return nextHours + ":" + minutes + " " + nextMeridiem;
}
and using above function as
var timestr="9:00 am";
var next_hour = increaseTimeByOne(timeStr);
alert(next_hour);

refer this
var time=new Date();
time.setHours(9, 00, 00);
var nexttime=(time.getHours()+1);
alert(nexttime);
// to get hrs mins and seconds
var nexttime=(time.getHours()+1) +":"+time.getMinutes()+":"+time.getSeconds();

YOu can make your time string like:
function increaseTimeByOne(t) {
var s = t.split(':');
var n = parseInt(s[0], 10);
var nt = (n + 1) + ":00 ";
var ampm = n >= 11 ? "pm" : "am";
return t + " - " + nt + ampm;
}
console.log(increaseTimeByOne('9:00 am'));
console.log(increaseTimeByOne('11:00 am'));
console.log(increaseTimeByOne('12:00 pm'));

convert time 12 hour format to 24 hour format and vice-versa

I want a js script that converts inputted time to 24 hour format or 12 hour format.
Example,
time is entered as 10_10_am result should be:-
10:10 AM (12 hr format) and 10:10 (24 hr format)
time is entered as 10_10_pm result should be:-
10:10 PM (12 hr format) and 22:10 (24 hr format)

HTML
<input type="text" id="textbox1"/>
<input type="button" id="b1" value="convert 12 hr"/>
<input type="button" id="b2" value="convert 24 hr"/>
<div id="result"></div>
JS
$(document).ready(function () {
function am_pm_to_hours(time) {
console.log(time);
var hours = Number(time.match(/^(\d+)/)[1]);
var minutes = Number(time.match(/:(\d+)/)[1]);
var AMPM = time.match(/\s(.*)$/)[1];
if (AMPM == "pm" && hours < 12) hours = hours + 12;
if (AMPM == "am" && hours == 12) hours = hours - 12;
var sHours = hours.toString();
var sMinutes = minutes.toString();
if (hours < 10) sHours = "0" + sHours;
if (minutes < 10) sMinutes = "0" + sMinutes;
return (sHours +':'+sMinutes);
}
function hours_am_pm(time) {
var hours = time[0] + time[1];
var min = time[2] + time[3];
if (hours < 12) {
return hours + ':' + min + ' AM';
} else {
hours=hours - 12;
hours=(hours.length < 10) ? '0'+hours:hours;
return hours+ ':' + min + ' PM';
}
}
$('#b1').click(function(){
var n = $('#textbox1').val();
var n1 =n.split('_');
var time = hours_am_pm(n1[0]+n1[1]);
$('#result').text(time);
});
$('#b2').click(function(){
var n = $('#textbox1').val();
var n1 =n.split('_');
var time = am_pm_to_hours(n1[0]+':'+n1[1]+' '+n1[2]);
$('#result').text(time);
});
});
Working Demo http://jsfiddle.net/cse_tushar/xEuUR/
updated after Adrian P 's comment
Working Demo http://jsfiddle.net/cse_tushar/xEuUR/4
function hours_am_pm(time) {
var hours = Number(time.match(/^(\d+)/)[1]);
var min = Number(time.match(/:(\d+)/)[1]);
if (min < 10) min = "0" + min;
if (hours < 12) {
return hours + ':' + min + ' AM';
} else {
hours=hours - 12;
hours=(hours < 10) ? '0'+hours:hours;
return hours+ ':' + min + ' PM';
}
}

I am not sure if there is any specific function that already exists, but this is fairly easy to write.
Considering your input is always ##_##_pm or ##_##_am you can split this string on every _ and grab first value as hours, second as minutes and compare the third
and
if it's pm add 12 hours to the hours variable for 24 hr format.
You need a function that takes 2 parameters (format and string)
It will look something like this:
function timeFormat(format, str){
var timeParts=str.split("_");
if(format==12){
return timeParts[0] + ":" + timeParts[1] + " " + timeParts[2];
}else if(format == 24){
var hours = timeParts[0];
if(timeParts[2] == "pm")
hours += 12;
return hours + ":" + timeParts[1]
}
}

convert 12-hour hh:mm AM/PM to 24-hour hh:mm

Is there any simple way to convert 12-hour hh:mm AM/PM to 24-hour hh:mm using jquery?
Note: not using any other libraries.
I have a var time = $("#starttime").val() that returns a hh:mm AM/PM.

Try this
var time = $("#starttime").val();
var hours = Number(time.match(/^(\d+)/)[1]);
var minutes = Number(time.match(/:(\d+)/)[1]);
var AMPM = time.match(/\s(.*)$/)[1];
if(AMPM == "PM" && hours<12) hours = hours+12;
if(AMPM == "AM" && hours==12) hours = hours-12;
var sHours = hours.toString();
var sMinutes = minutes.toString();
if(hours<10) sHours = "0" + sHours;
if(minutes<10) sMinutes = "0" + sMinutes;
alert(sHours + ":" + sMinutes);

This question needs a newer answer :)
const convertTime12to24 = (time12h) => {
const [time, modifier] = time12h.split(' ');
let [hours, minutes] = time.split(':');
if (hours === '12') {
hours = '00';
}
if (modifier === 'PM') {
hours = parseInt(hours, 10) + 12;
}
return `${hours}:${minutes}`;
}
console.log(convertTime12to24('01:02 PM'));
console.log(convertTime12to24('05:06 PM'));
console.log(convertTime12to24('12:00 PM'));
console.log(convertTime12to24('12:00 AM'));

This will help :
function getTwentyFourHourTime(amPmString) {
var d = new Date("1/1/2013 " + amPmString);
return d.getHours() + ':' + d.getMinutes();
}
Example :
getTwentyFourHourTime("8:45 PM"); // "20:45"
getTwentyFourHourTime("8:45 AM"); // "8:45"
Update :
Note : There should be a space for timestring between "Time" and "am/pm".

I had to do something similar but I was generating a Date object so I ended up making a function like this:
function convertTo24Hour(time) {
var hours = parseInt(time.substr(0, 2));
if(time.indexOf('am') != -1 && hours == 12) {
time = time.replace('12', '0');
}
if(time.indexOf('pm') != -1 && hours < 12) {
time = time.replace(hours, (hours + 12));
}
return time.replace(/(am|pm)/, '');
}
I think this reads a little easier. You feed a string in the format h:mm am/pm.
var time = convertTo24Hour($("#starttime").val().toLowerCase());
var date = new Date($("#startday").val() + ' ' + time);
Examples:
$("#startday").val('7/10/2013');
$("#starttime").val('12:00am');
new Date($("#startday").val() + ' ' + convertTo24Hour($("#starttime").val().toLowerCase()));
Wed Jul 10 2013 00:00:00 GMT-0700 (PDT)
$("#starttime").val('12:00pm');
new Date($("#startday").val() + ' ' + convertTo24Hour($("#starttime").val().toLowerCase()));
Wed Jul 10 2013 12:00:00 GMT-0700 (PDT)
$("#starttime").val('1:00am');
new Date($("#startday").val() + ' ' + convertTo24Hour($("#starttime").val().toLowerCase()));
Wed Jul 10 2013 01:00:00 GMT-0700 (PDT)
$("#starttime").val('12:12am');
new Date($("#startday").val() + ' ' + convertTo24Hour($("#starttime").val().toLowerCase()));
Wed Jul 10 2013 00:12:00 GMT-0700 (PDT)
$("#starttime").val('3:12am');
new Date($("#startday").val() + ' ' + convertTo24Hour($("#starttime").val().toLowerCase()));
Wed Jul 10 2013 03:12:00 GMT-0700 (PDT)
$("#starttime").val('9:12pm');
new Date($("#startday").val() + ' ' + convertTo24Hour($("#starttime").val().toLowerCase()));
Wed Jul 10 2013 21:12:00 GMT-0700 (PDT)

Here my solution including seconds:
function convert_to_24h(time_str) {
// Convert a string like 10:05:23 PM to 24h format, returns like [22,5,23]
var time = time_str.match(/(\d+):(\d+):(\d+) (\w)/);
var hours = Number(time[1]);
var minutes = Number(time[2]);
var seconds = Number(time[3]);
var meridian = time[4].toLowerCase();
if (meridian == 'p' && hours < 12) {
hours += 12;
}
else if (meridian == 'a' && hours == 12) {
hours -= 12;
}
return [hours, minutes, seconds];
};

function timeConversion(s) {
var time = s.toLowerCase().split(':');
var hours = parseInt(time[0]);
var _ampm = time[2];
if (_ampm.indexOf('am') != -1 && hours == 12) {
time[0] = '00';
}
if (_ampm.indexOf('pm') != -1 && hours < 12) {
time[0] = hours + 12;
}
return time.join(':').replace(/(am|pm)/, '');
}
Call the function with string params:
timeConversion('17:05:45AM')
or
timeConversion('07:05:45PM')

i must recommend a library: Moment
code:
var target12 = '2016-12-08 9:32:45 PM';
console.log(moment(target12, 'YYYY-MM-DD h:m:s A').format('YYYY-MM-DD HH:mm:ss'));

For anybody reading this in the future, here is a simpler answer:
var s = "11:41:02PM";
var time = s.match(/\d{2}/g);
if (time[0] === "12") time[0] = "00";
if (s.indexOf("PM") > -1) time[0] = parseInt(time[0])+12;
return time.join(":");

Single line code for calc time 12 hours to 24 hours
Any format of the input working fine
const convertTime12to24 = (time12h) => moment(time12h, 'hh:mm A').format('HH:mm');
console.log(convertTime12to24('06:30 pm'));
console.log(convertTime12to24('06:00 am'));
console.log(convertTime12to24('9:00 am'));
console.log(convertTime12to24('9pm'));
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.29.1/moment.min.js"></script>

In case you're looking for a solution that converts ANY FORMAT to 24 hours HH:MM correctly.
function get24hTime(str) {
str = String(str).toLowerCase().replace(/\s/g, '');
var has_am = str.indexOf('am') >= 0;
var has_pm = str.indexOf('pm') >= 0;
// first strip off the am/pm, leave it either hour or hour:minute
str = str.replace('am', '').replace('pm', '');
// if hour, convert to hour:00
if (str.indexOf(':') < 0) str = str + ':00';
// now it's hour:minute
// we add am/pm back if striped out before
if (has_am) str += ' am';
if (has_pm) str += ' pm';
// now its either hour:minute, or hour:minute am/pm
// put it in a date object, it will convert to 24 hours format for us
var d = new Date("1/1/2011 " + str);
// make hours and minutes double digits
var doubleDigits = function(n) {
return (parseInt(n) < 10) ? "0" + n : String(n);
};
return doubleDigits(d.getHours()) + ':' + doubleDigits(d.getMinutes());
}
console.log(get24hTime('6')); // 06:00
console.log(get24hTime('6am')); // 06:00
console.log(get24hTime('6pm')); // 18:00
console.log(get24hTime('6:11pm')); // 18:11
console.log(get24hTime('6:11')); // 06:11
console.log(get24hTime('18')); // 18:00
console.log(get24hTime('18:11')); // 18:11

I needed this function for a project. I tried devnull69's but I was having some trouble, mostly because the string input is very specific for the am/pm section and I would've needed to change my validation. I messed around with Adrian P.'s jsfiddle and ended up with a version that seems to work better for a larger variety of date formats. Here is the fiddle: http://jsfiddle.net/u91q8kmt/2/.
Here is the function:
function ConvertTimeformat(format, str) {
var hours = Number(str.match(/^(\d+)/)[1]);
var minutes = Number(str.match(/:(\d+)/)[1]);
var AMPM = str.match(/\s?([AaPp][Mm]?)$/)[1];
var pm = ['P', 'p', 'PM', 'pM', 'pm', 'Pm'];
var am = ['A', 'a', 'AM', 'aM', 'am', 'Am'];
if (pm.indexOf(AMPM) >= 0 && hours < 12) hours = hours + 12;
if (am.indexOf(AMPM) >= 0 && hours == 12) hours = hours - 12;
var sHours = hours.toString();
var sMinutes = minutes.toString();
if (hours < 10) sHours = "0" + sHours;
if (minutes < 10) sMinutes = "0" + sMinutes;
if (format == '0000') {
return (sHours + sMinutes);
} else if (format == '00:00') {
return (sHours + ":" + sMinutes);
} else {
return false;
}
}

With this you can have the following:
Sample Input: 07:05:45PM
Sample Output: 19:05:45
function timeConversion(s) {
let output = '';
const timeSeparator = ':'
const timeTokenType = s.substr(s.length - 2 , 2).toLowerCase();
const timeArr = s.split(timeSeparator).map((timeToken) => {
const isTimeTokenType =
timeToken.toLowerCase().indexOf('am') > 0 ||
timeToken.toLowerCase().indexOf('pm');
if(isTimeTokenType){
return timeToken.substr(0, 2);
} else {
return timeToken;
}
});
const hour = timeArr[0];
const minutes = timeArr[1];
const seconds = timeArr[2];
const hourIn24 = (timeTokenType === 'am') ? parseInt(hour) - 12 :
parseInt(hour) + 12;
return hourIn24.toString()+ timeSeparator + minutes + timeSeparator + seconds;
}
Hope you like it !

Because all the answers so far seem to be verbose, here's a simple minimalist solution:
/* Convert h:mm a/p to H:mm
* i.e. 12 hour time to 24 hour time
* #param {string} time - h:mm a/p format
* #returns {string} time in H:mm format
*/
function to24HrTime(time) {
let [hr, min, ap] = time.toLowerCase().match(/\d+|[a-z]+/g) || [];
return `${(hr % 12) + (ap == 'am'? 0 : 12)}:${min}`;
}
['9:02 am',
'9:02 pm',
'9:02am',
'9:02pm',
'12:15 AM',
'12:01 PM',
].forEach(time => console.log(`${time} -> ${to24HrTime(time)}`));
That assumes the input string has a suitable format and values. A more robust version is:
/* Given 12 hr time, return24 hr time
* #param {string} time - time in format h:mm am/pm
* h must be in range 1 to 12
* mm must be in range 00 to 59
* am/pm is not case sensitive
* #returns {string} time in 24 hr format H:mm
* H in range 0 to 23
* mm in range 00 to 59
*
*/
function to24HrTime(time = new Date().toLocaleString('en',{hour:'numeric', minute:'2-digit', hour12:true})) {
let [hr, min, ap] = String(time).toLowerCase().match(/\d+|[a-z]+/g) || [];
// If time is valid, return reformatted time
// Otherwise return undefined
return /^([1-9]|1[0-2]):[0-5]\d\s?(am|pm)/i.test(time)? `${(hr%12)+(ap=='am'?0:12)}:${min}` : void 0;
}
// Examples
// Without arguments
console.log(`No args -> ${to24HrTime()}`);
// Valid input
['9:02 am',
'9:02 pm',
'9:02am',
'9:02pm',
'12:15 AM',
'12:01 PM',
// Invalid input
'12', // Missing mins & ap
'99:05 am', // hrs out of range
'0:05 am', // hrs out of range
'9:60 am', // mins out of range
'9:09 pp', // ap out of range
{}, // Random object
].forEach(time => console.log(`${time} -> ${to24HrTime(time)}`));

An extended version of #krzysztof answer with the ability to work on time that has space or not between time and modifier.
const convertTime12to24 = (time12h) => {
const [fullMatch, time, modifier] = time12h.match(/(\d?\d:\d\d)\s*(\w{2})/i);
let [hours, minutes] = time.split(':');
if (hours === '12') {
hours = '00';
}
if (modifier === 'PM') {
hours = parseInt(hours, 10) + 12;
}
return `${hours}:${minutes}`;
}
console.log(convertTime12to24('01:02 PM'));
console.log(convertTime12to24('05:06 PM'));
console.log(convertTime12to24('12:00 PM'));
console.log(convertTime12to24('12:00 AM'));

based on meeting CodeSkill #1
validation of format should be another function :)
function convertTimeFrom12To24(timeStr) {
var colon = timeStr.indexOf(':');
var hours = timeStr.substr(0, colon),
minutes = timeStr.substr(colon+1, 2),
meridian = timeStr.substr(colon+4, 2).toUpperCase();
var hoursInt = parseInt(hours, 10),
offset = meridian == 'PM' ? 12 : 0;
if (hoursInt === 12) {
hoursInt = offset;
} else {
hoursInt += offset;
}
return hoursInt + ":" + minutes;
}
console.log(convertTimeFrom12To24("12:00 AM"));
console.log(convertTimeFrom12To24("12:00 PM"));
console.log(convertTimeFrom12To24("11:00 AM"));
console.log(convertTimeFrom12To24("01:00 AM"));
console.log(convertTimeFrom12To24("01:00 PM"));

Converting AM/PM Time string to 24 Hours Format.
Example 9:30 PM to 21:30
function get24HrsFrmAMPM(timeStr) {
if (timeStr && timeStr.indexOf(' ') !== -1 && timeStr.indexOf(':') !== -1) {
var hrs = 0;
var tempAry = timeStr.split(' ');
var hrsMinAry = tempAry[0].split(':');
hrs = parseInt(hrsMinAry[0], 10);
if ((tempAry[1] == 'AM' || tempAry[1] == 'am') && hrs == 12) {
hrs = 0;
} else if ((tempAry[1] == 'PM' || tempAry[1] == 'pm') && hrs != 12) {
hrs += 12;
}
return ('0' + hrs).slice(-2) + ':' + ('0' + parseInt(hrsMinAry[1], 10)).slice(-2);
} else {
return null;
}
}

//here is my solution.
function timeConversion(s) {
// Write your code here
let amPM = s.indexOf('AM') !== -1 ? 'AM' : 'PM';
let tString = s.toString().replace(/AM|PM/gi,'');
let splitTime = tString.split(':');
let h = splitTime[0];
let m = splitTime[1];
let sec = splitTime[2];
let twntyfr = amPM === 'PM' && parseInt(h) !== 12 ? parseInt(h)+12 : h;
if(parseInt(twntyfr) === 12 && amPM === 'AM') twntyfr = '00';
return twntyfr+':'+m+':'+sec;
}

HackerRank TimeConversion Solution
12-hour AM/PM format, to military (24-hour) time
function timeConversion(s) {
let time = 0
let hour = s.slice(0, 2)
let toD = s.slice(-2)
if (toD === 'AM' && hour == 12) {
time = `00${s.slice(2, s.length -2)}`
} else {
if (toD === 'PM' && hour < 12) {
time = `${Number(12 + parseInt(hour))}${s.slice(2, s.length - 2)}`
} else {
time = s.slice(0, s.length - 2)
}
}
return console.log(time)
}
timeConversion('12:00:17AM') // 00:00:17
timeConversion('09:21:33PM') // 21:21:33
timeConversion('12:43:53PM') // 12:43:53

function getDisplayDatetime() {
var d = new Date("February 04, 2011 19:00"),
hh = d.getHours(), mm = d.getMinutes(), dd = "AM", h = hh;
mm=(mm.toString().length == 1)? mm = "0" + mm:mm;
h=(h>=12)?hh-12:h;
dd=(hh>=12)?"PM":"AM";
h=(h == 0)?12:h;
var textvalue=document.getElementById("txt");
textvalue.value=h + ":" + mm + " " + dd;
}
</script>
</head>
<body>
<input type="button" value="click" onclick="getDisplayDatetime()">
<input type="text" id="txt"/>

dateFormat.masks.armyTime= 'HH:MM';
now.format("armyTime");

function convertTo24Hour(time) {
time = time.toUpperCase();
var hours = parseInt(time.substr(0, 2));
if(time.indexOf('AM') != -1 && hours == 12) {
time = time.replace('12', '0');
}
if(time.indexOf('PM') != -1 && hours < 12) {
time = time.replace(hours, (hours + 12));
}
return time.replace(/(AM|PM)/, '');
}

date --date="2:00:01 PM" +%T
14:00:01
date --date="2:00 PM" +%T | cut -d':' -f1-2
14:00
var="2:00:02 PM"
date --date="$var" +%T
14:00:02

You could try this more generic function:
function from12to24(hours, minutes, meridian) {
let h = parseInt(hours, 10);
const m = parseInt(minutes, 10);
if (meridian.toUpperCase() === 'PM') {
h = (h !== 12) ? h + 12 : h;
} else {
h = (h === 12) ? 0 : h;
}
return new Date((new Date()).setHours(h,m,0,0));
}
Note it uses some ES6 functionality.

I've created a bit of an adaptation of script #devnull69 submitted. I felt for my application it would be more useful as a function that returned the value that I could, then use as a variable.
HTML
<input type="text" id="time_field" />
<button>Submit</submit>
jQuery
$(document).ready(function() {
function convertTime(time) {
var hours = Number(time.match(/^(\d\d?)/)[1]);
var minutes = Number(time.match(/:(\d\d?)/)[1]);
var AMPM = time.match(/\s(AM|PM)$/i)[1];
if((AMPM == 'PM' || AMPM == 'pm') && hours < 12) {
hours = hours + 12;
}
else if((AMPM == 'AM' || AMPM == "am") && hours == 12) {
hours = hours - 12;
}
var sHours = hours.toString();
var sMinutes = minutes.toString();
if(hours < 10) {
sHours = "0" + sHours;
}
else if(minutes < 10) {
sMinutes = "0" + sMinutes;
}
return sHours + ":" + sMinutes;
}
$('button').click(function() {
alert(convertTime($('#time_field').val()));
});
});

single and easy js function for calc time meridian in real time
JS
function convertTime24to12(time24h) {
var timex = time24h.split(':');
if(timex[0] !== undefined && timex [1] !== undefined)
{
var hor = parseInt(timex[0]) > 12 ? (parseInt(timex[0])-12) : timex[0] ;
var minu = timex[1];
var merid = parseInt(timex[0]) < 12 ? 'AM' : 'PM';
var res = hor+':'+minu+' '+merid;
document.getElementById('timeMeridian').innerHTML=res.toString();
}
}
Html
<label for="end-time">Hour <i id="timeMeridian"></i> </label>
<input type="time" name="hora" placeholder="Hora" id="end-time" class="form-control" onkeyup="convertTime24to12(this.value)">

Typescript solution based off of #krzysztof-dąbrowski 's answer
export interface HoursMinutes {
hours: number;
minutes: number;
}
export function convert12to24(time12h: string): HoursMinutes {
const [time, modifier] = time12h.split(' ');
let [hours, minutes] = time.split(':');
if (hours === '12') {
hours = '00';
}
if (minutes.length === 1) {
minutes = `0${minutes}`;
}
if (modifier.toUpperCase() === 'PM') {
hours = parseInt(hours, 10) + 12 + '';
}
return {
hours: parseInt(hours, 10),
minutes: parseInt(minutes, 10)
};
}

Tested for all the use cases
function timeConversion(s) {
let h24;
let m24;
let sec24;
const splittedDate = s.split(":");
const h = parseInt(splittedDate[0], 10);
const m = parseInt(splittedDate[1], 10);
const sec = parseInt(splittedDate[2][0] + splittedDate[2][1], 10);
const meridiem = splittedDate[2][2] + splittedDate[2][3];
if (meridiem === "AM") {
if (h === 12) {
h24 = '00';
} else {
h24 = h;
if (h24 < 10) {
h24 = '0' + h24;
}
}
m24 = m;
sec24 = sec;
} else if (meridiem === "PM") {
if (h === 12) {
h24 = h
} else {
h24 = h + 12;
if (h24 < 10) {
h24 = '0' + h24;
}
}
m24 = m;
sec24 = sec;
}
if (m24 < 10) {
m24 = '0' + m24;
}
if (sec24 < 10) {
sec24 = '0' + sec24;
}
return h24 + ":" + m24 + ":" + sec24;
}
Here is the jsfiddle working example

Short ES6 code
const convertFrom12To24Format = (time12) => {
const [sHours, minutes, period] = time12.match(/([0-9]{1,2}):([0-9]{2}) (AM|PM)/).slice(1);
const PM = period === 'PM';
const hours = (+sHours % 12) + (PM ? 12 : 0);
return `${('0' + hours).slice(-2)}:${minutes}`;
}
const convertFrom24To12Format = (time24) => {
const [sHours, minutes] = time24.match(/([0-9]{1,2}):([0-9]{2})/).slice(1);
const period = +sHours < 12 ? 'AM' : 'PM';
const hours = +sHours % 12 || 12;
return `${hours}:${minutes} ${period}`;
}

I just solved this issue on HackerRank, so I'm here to share my result
function timeConversion(s) {
const isPM = s.indexOf('PM') !== -1;
let [hours, minutes, seconds] = s.replace(isPM ? 'PM':'AM', '').split(':');
if (isPM) {
hours = parseInt(hours, 10) + 12;
hours = hours === 24 ? 12 : hours;
} else {
hours = parseInt(hours, 10);
hours = hours === 12 ? 0 : hours;
if (String(hours).length === 1) hours = '0' + hours;
}
const time = [hours, minutes, seconds].join(':');
return time;
}
This works for inputs like 06:40:03AM.

function formatto24(date) {
let ampm = date.split(" ")[1];
let time = date.split(" ")[0];
if (ampm == "PM") {
let hours = time.split(":")[0];
let minutes = time.split(":")[1];
let seconds = time.split(":")[2];
let hours24 = JSON.parse(hours) + 12;
return hours24 + ":" + minutes + ":" + seconds;
} else {
return time;
}
}