Converting milliseconds to a date (jQuery/JavaScript)

Deciphering the date object

To dissect a date object into its components:

let date = new Date(ms);
console.log(date.getFullYear());          // "2019" Hope I looked good in photos!
console.log(date.getMonth() + 1);         // "12" *Ahem* Remember, month starts at 0.
console.log(date.getDate());              // "9" On this day...
console.log(date.toDateString());         // "Mon Dec 09 2019" Weekday included for a party plan.
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Localizing the dates in your favor

Emphasizing locale and timezone, toLocaleString() is a lifesaver:

console.log(date.toLocaleString("en-US", { timeZone: "America/New_York" }));  // "12/9/2019, 5:30:15 AM" Quite early, in the "Big Apple".
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Adjust to suit locale formats:

console.log(date.toLocaleString("en-GB")); // "09/12/2019, 10:30:15" Brits like their dates reversed!
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Easy date formatting with third-party libraries

When basic functionality won't suffice, libraries like Moment.js or Day.js can help:

// With Moment.js
console.log(moment(ms).format("DD/MM/YYYY HH:mm:ss")); // "09/12/2019 10:30:15" In moments, we made it!
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Custom date formatting to your rescue

In need of custom formatting? Create your formatter:

function customFormat(date) {
    let dd = date.getDate();
    let mm = date.getMonth() + 1; // January is 0! *winks*
    let yyyy = date.getFullYear();
    
    // Single digit days and months feel left out. So, they get a 0 pal!
    dd = dd < 10 ? '0' + dd : dd;
    mm = mm < 10 ? '0' + mm : mm;
    
    return `${dd}/${mm}/${yyyy}`;
}

console.log(customFormat(new Date(ms))); // "09/12/2019"
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Formatting dates: Putting user first

Different users, different formats. Add options to keep everyone happy:

function userPreferredDateFormat(date, format) {
    // An example implementation with day.js
    return dayjs(date).format(format);
}

console.log(userPreferredDateFormat(new Date(ms), "YYYY-MM-DD")); // "2019-12-09" And they lived happily ever after!
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Advance moves: Time traveling

Ever wished to add or subtract time? Here you go:

let tomorrowMs = ms + (24 * 60 * 60 * 1000);
console.log(new Date(tomorrowMs).toLocaleDateString()); // "12/10/2019" Welcome, tomorrow!
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Tackling tricky edge cases

Sometimes, edge cases aren't so edgy. Be wary of leap seconds, time zone deviations, and browser quirks.

Displaying the date: All eyes on this

Finally, don't let your efforts go unnoticed:

document.body.textContent = new Date(ms).toString(); // "That's one small step for man, one giant leap for mankind."
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