Develop Reference

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>

Page last modified using Javascript with 12 hour clock showing am or pm

I'm trying to create a script in Javascript that shows when a page was last modified, which returns the date, time, in am or pm format, of modification.
Clearly I am doing something wrong. I can't get the script to run, and it will be in my function AmPm. Can someone please help?
// Javascript code for page modification
// Shows the date, time, am or pm, of modification.
// This section sets the date of modification
function lastModified() {
var modiDate = new Date(document.lastModified);
var showAs = modiDate.getDate() + "." + (modiDate.getMonth() + 1) + "." + modiDate.getFullYear();
return showAs
}
// This section sets the time of modification
function GetTime() {
var modiDate = new Date();
var Seconds
if (modiDate.getSeconds() < 10) {
Seconds = "0" + modiDate.getSeconds();
} else {
Seconds = modiDate.getSeconds();
}
// This section writes the above in the document
var modiDate = new Date();
var CurTime = modiDate.getHours() + ":" + modiDate.getMinutes() + ":" + Seconds
return CurTime
}
// This section decides if its am or pm
function AmPm() {
var hours = new Date().getHours();
var hours = (hours + 24 - 2) % 24;
var mid = 'AM';
if (hours == 0) { // At 00 hours (midnight) we need to display 12 am
hours = 12;
} else if (hours > 12) // At 12pm (Midday) we need to display 12 pm
{
hours = hours % 12;
mid = 'PM';
}
}
var mid = //This is where I am stuck!!
return AmPm
document.write("This webpage was last edited on: ");
document.write(lastModified() + " at " + GetTime() + AmPm());
document.write("");
document.write(" NZ Daylight Savings Time.");
document.write("");

function formatAMPM(date) {
var hours = date.getHours();
var minutes = date.getMinutes();
var ampm = hours >= 12 ? 'pm' : 'am';
hours = hours % 12;
hours = hours ? hours : 12; // the hour '0' should be '12'
minutes = minutes < 10 ? '0'+minutes : minutes;
var strTime = hours + ':' + minutes + ' ' + ampm;
return strTime;
}

JQuery Datepicker - setting MinDate based on current time

I'm using JQuery Datepicker for customers to choose a delivery date. I want to be able to check if the customer is ordering before noon and if so next day delivery is available. If they are ordering after noon, next day delivery is unavailable and so that day is unselectable.
I've got some code to check against the current time but how to I add this value into MinDate in the settings at the top?
Thank you!
<div class="delivery-date">
<p>
<label for="date">Select a date for delivery below:</label>
<input id="date" type="text" name="properties[delivery-date]" readonly="readonly" style="background:white; width:30%" class="required" data-error="Please choose a delivery date." />
</p>
</div>
<script>
jQuery(function() {
jQuery("#date").datepicker( {
// minDate: new Date(((new Date).getTime() + 49 * 60 * 60 * 1000) ),
minDate: checkBeforeNoon,
maxDate: "+2M", // show up to 2 months
dateFormat: 'dd/mm/yy',
beforeShowDay: available_delivery_dates
} );
});
/*========== check time ==========*/
// if time before 12pm, offer next day delivery
function checkBeforeNoon(nextDayDelivery){
var startTime = '12:00 AM';
var endTime = '12:00 PM';
var curr_time = getval();
if (get24Hr(curr_time) > get24Hr(startTime) && get24Hr(curr_time) < get24Hr(endTime)) {
// before 12pm - next day delivery available
var nextDayDelivery = '+1d';
} else {
// after 12pm - next day delivery unavailable
var nextDayDelivery = '+2d';
}
function get24Hr(time){
var hours = 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 minutes = Number(time.match(/:(\d+)/)[1]);
hours = hours*100+minutes;
console.log(time +" - "+hours);
return hours;
}
function getval() {
var currentTime = new Date()
var hours = currentTime.getHours()
var minutes = currentTime.getMinutes()
if (minutes < 10) minutes = "0" + minutes;
var suffix = "AM";
if (hours >= 12) {
suffix = "PM";
hours = hours - 12;
}
if (hours == 0) {
hours = 12;
}
var current_time = hours + ":" + minutes + " " + suffix;
return current_time;
}
}
/*========== Make sundays always unavailable ==========*/
function available_delivery_dates(date) {
var sunday = 0; // unavailable for delivery
var mon = 1
var tue = 2;
var wed = 3;
var thu = 4;
var fri = 5;
var sat = 6;
var day_of_week = date.getDay();
var not_sun = day_of_week > 0;
if(not_sun){
var day = date.getDate();
return [true, ''];
}
else{
// all else - do not allow
return [false, ' ', 'Delivery is unavailable on this day'];
}
}
</script>

You already accomplished it. You simply need to add a return to the function that is checking if it is noon. If you want to advise the client that one day shipping is available now, you can do so by adding a log in your function. Here is your code modified:
http://jsfiddle.net/graphicfreedom/L3tz8243/1/
function checkBeforeNoon(nextDayDelivery){
var startTime = '12:00 AM';
var endTime = '12:00 PM';
var curr_time = getval();
if (get24Hr(curr_time) > get24Hr(startTime) && get24Hr(curr_time) < get24Hr(endTime)) {
// before 12pm - next day delivery available
var nextDayDelivery = '+1d';
$("#log").html('Next day delivery available! Order before noon!'); //show response to user
} else {
// after 12pm - next day delivery unavailable
var nextDayDelivery = '+2d';
$("#log").html('Next day delivery NOT available! It is already past noon :('); //show response to user
}
return nextDayDelivery;
}
Also, you can easily separate the functions. It is easier to read, and you can always call a function from a function. Hope this helps!

Remove the var before nextDayDelivery in the if-else block as you would be redeclaring it. Then return nextDayDelivery. Also, a good idea to fix the missing semi-colons in the getVal() method.
function checkBeforeNoon(nextDayDelivery) {
var startTime = '12:00 AM';
var endTime = '12:00 PM';
var curr_time = getval();
if (get24Hr(curr_time) > get24Hr(startTime) && get24Hr(curr_time) < get24Hr(endTime)) {
// before 12pm - next day delivery available
nextDayDelivery = '+1d'; // REMOVE var FROM HERE
} else {
// after 12pm - next day delivery unavailable
nextDayDelivery = '+2d'; // REMOVE var FROM HERE
}
function get24Hr(time) {
var hours = 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 minutes = Number(time.match(/:(\d+)/)[1]);
hours = hours * 100 + minutes;
console.log(time + " - " + hours);
return hours;
}
function getval() {
// ADD MISSING SEMI-COLONS ON THE FOLLOWING 3 LINES
var currentTime = new Date();
var hours = currentTime.getHours();
var minutes = currentTime.getMinutes();
if (minutes < 10) minutes = "0" + minutes;
var suffix = "AM";
if (hours >= 12) {
suffix = "PM";
hours = hours - 12;
}
if (hours == 0) {
hours = 12;
}
var current_time = hours + ":" + minutes + " " + suffix;
return current_time;
}
return nextDayDelivery; // ADD RETURN STATEMENT
}

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;
}
}

javascript date conversion

I want to take an existing javascript string and convert it javascript timestamp object,
then store as format YYYYMMDDHHMMSS
mystring = "Mon Nov 07 2011 09:20:58 GMT-0500 (Eastern Standard Time)";
var timeObject = new Date(mystring);

// pass in javascript date object, return variations of YYYY-MM-DD HH:MM:SS
function fnFormatDateTime(timeObject)
{
// construct day/month/year
var month = timeObject.getMonth() + 1;
if (month < 10){
month = "0" + month;
}
var day = timeObject.getDate();
if (day < 10){
day = "0" + day;
}
var year = timeObject.getFullYear();
var currentDate = (" " + year + month + day).trim();
var currentDateFormatted = ( year +"-"+ month +"-"+ day);
// construct current time
var hours = timeObject.getHours();
if (hours < 10){
hours = "0" + hours;
}
var minutes = timeObject.getMinutes();
if (minutes < 10){
minutes = "0" + minutes;
}
var seconds = timeObject.getSeconds();
if (seconds < 10){
seconds = "0" + seconds;
}
var currentTime = (hours + minutes + seconds + " ").trim();
var currentTimeFormatted = (hours +":"+ minutes +":"+ seconds);
var retArray = new Array();
retArray[0] = (currentDateFormatted + " " + currentTimeFormatted);
retArray[1] = (currentDate+ " " + currentTime);
retArray[2] = currentDate;
retArray[3] = currentTime;
return retArray;
}