If you prefer to resolve timestamps and dates conversions from and to UTC and local time without libraries like moment.js, take a look at the option below.
For applications that use UTC timestamps, you may need to show the date in the browser considering the local timezone and daylight savings when applicable. Editing a date that is in a different daylight savings time even though in the same timezone can be tricky.
The Number and Date extensions below allow you to show and get dates in the timezone of the timestamps. For example, lets say you are in Vancouver, if you are editing a date in July or in December, it can mean you are editing a date in PST or PDT.
I recommend you to check the Code Snippet down below to test this solution.
Conversions from milliseconds
Number.prototype.toLocalDate = function () {
var value = new Date(this);
value.setHours(value.getHours() + (value.getTimezoneOffset() / 60));
return value;
};
Number.prototype.toUTCDate = function () {
var value = new Date(this);
value.setHours(value.getHours() - (value.getTimezoneOffset() / 60));
return value;
};
Conversions from dates
Date.prototype.getUTCTime = function () {
return this.getTime() - (this.getTimezoneOffset() * 60000);
};
Usage
// Adds the timezone and daylight savings if applicable
(1499670000000).toLocalDate();
// Eliminates the timezone and daylight savings if applicable
new Date(2017, 6, 10).getUTCTime();
See it for yourself
// Extending Number
Number.prototype.toLocalDate = function () {
var value = new Date(this);
value.setHours(value.getHours() + (value.getTimezoneOffset() / 60));
return value;
};
Number.prototype.toUTCDate = function () {
var value = new Date(this);
value.setHours(value.getHours() - (value.getTimezoneOffset() / 60));
return value;
};
// Extending Date
Date.prototype.getUTCTime = function () {
return this.getTime() - (this.getTimezoneOffset() * 60000);
};
// Getting the demo to work
document.getElementById('m-to-local-button').addEventListener('click', function () {
var displayElement = document.getElementById('m-to-local-display'),
value = document.getElementById('m-to-local').value,
milliseconds = parseInt(value);
if (typeof milliseconds === 'number')
displayElement.innerText = (milliseconds).toLocalDate().toISOString();
else
displayElement.innerText = 'Set a value';
}, false);
document.getElementById('m-to-utc-button').addEventListener('click', function () {
var displayElement = document.getElementById('m-to-utc-display'),
value = document.getElementById('m-to-utc').value,
milliseconds = parseInt(value);
if (typeof milliseconds === 'number')
displayElement.innerText = (milliseconds).toUTCDate().toISOString();
else
displayElement.innerText = 'Set a value';
}, false);
document.getElementById('date-to-utc-button').addEventListener('click', function () {
var displayElement = document.getElementById('date-to-utc-display'),
yearValue = document.getElementById('date-to-utc-year').value || '1970',
monthValue = document.getElementById('date-to-utc-month').value || '0',
dayValue = document.getElementById('date-to-utc-day').value || '1',
hourValue = document.getElementById('date-to-utc-hour').value || '0',
minuteValue = document.getElementById('date-to-utc-minute').value || '0',
secondValue = document.getElementById('date-to-utc-second').value || '0',
year = parseInt(yearValue),
month = parseInt(monthValue),
day = parseInt(dayValue),
hour = parseInt(hourValue),
minute = parseInt(minuteValue),
second = parseInt(secondValue);
displayElement.innerText = new Date(year, month, day, hour, minute, second).getUTCTime();
}, false);
<link href="https://cdnjs.cloudflare.com/ajax/libs/semantic-ui/2.2.11/semantic.css" rel="stylesheet"/>
<div class="ui container">
<p></p>
<h3>Milliseconds to local date</h3>
<input id="m-to-local" placeholder="Timestamp" value="0" /> <button id="m-to-local-button">Convert</button>
<em id="m-to-local-display">Set a value</em>
<h3>Milliseconds to UTC date</h3>
<input id="m-to-utc" placeholder="Timestamp" value="0" /> <button id="m-to-utc-button">Convert</button>
<em id="m-to-utc-display">Set a value</em>
<h3>Date to milliseconds in UTC</h3>
<input id="date-to-utc-year" placeholder="Year" style="width: 4em;" />
<input id="date-to-utc-month" placeholder="Month" style="width: 4em;" />
<input id="date-to-utc-day" placeholder="Day" style="width: 4em;" />
<input id="date-to-utc-hour" placeholder="Hour" style="width: 4em;" />
<input id="date-to-utc-minute" placeholder="Minute" style="width: 4em;" />
<input id="date-to-utc-second" placeholder="Second" style="width: 4em;" />
<button id="date-to-utc-button">Convert</button>
<em id="date-to-utc-display">Set the values</em>
</div>
