Infinite Unixtime

Online Demo

Quick Start

npm install infinite-unixtime

CDN Build Example

• Download CDN Build

<script src="./infinite-unixtime-1.1.4.min.js"></script>
<pre id="result"></pre>
<script type="text/javascript">
    // If 'Unixtime' is already in use, you can use '$Unixtime' instead.
    // Example
    let w = '';
    w += Unixtime.now() + '\n'
    w += Unixtime.fromMillis(123456333242347890123) + '\n'
    // 23948923423421773421234-01-31T00:00:00.000Z
    w += Unixtime.fromUtc(23948923423421773421234n, 1, 31).toIsoStringUtc() + '\n';
    // -3472472928838222222282881717114-12-31T14:59:59.999Z
    w += Unixtime.from(-3472472928838222222282881717114n, 12, 31, 23, 59, 59, 999).toIsoStringUtc() + '\n';
    document.getElementById('result').innerText = w;
</script>

Features

• Infinite Time Support

console.log(Unixtime.fromUtc(23948921773421234n, 1, 31).toIsoStringUtc());
console.log(Unixtime.from(-3472472928838282881717114n, 12, 31).toIsoStringUtc());

• Ignore LMT(Local mean time)
• Guarantees a consistent timezone offset across all eras, bypassing the historic LMT shifts often found in native environment implementations.

// Example: Asia/Seoul (+09:00)

// Native JavaScript Date applies LMT for older dates
new Date(2000, 0, 1)
// -> Sat Jan 01 2000 00:00:00 GMT+0900 (Korean Standard Time)
new Date(1900, 0, 1)
// -> Mon Jan 01 1900 00:00:00 GMT+0827 (Korean Standard Time)
// Note the +08:27 LMT shift

// Unixtime maintains the same timezone offset consistently
Unixtime.from(2000, 1, 1).toString()
// -> 2000-01-01 (Sat) AM 00:00 00.000 +09:00
Unixtime.from(1900, 1, 1).toString()
// -> 1900-01-01 (Mon) AM 00:00 00.000 +09:00
// Maintain Same Timezone

Example

From unixtime (milliseconds / seconds)

let u = Unixtime.fromMillis(0);
assert.equal(u.toIsoStringUtc(), '1970-01-01T00:00:00.000Z');
assert.equal(u.toIsoString(-540), '1970-01-01T09:00:00.000+09:00');
assert.equal(u.toIsoString(-720), '1970-01-01T12:00:00.000+12:00');
assert.equal(u.toIsoString(720), '1969-12-31T12:00:00.000-12:00');
console.log(u.toIsoStringUtc());
console.log();

u = Unixtime.fromSeconds(0);
assert.equal(u.toIsoStringUtc(), '1970-01-01T00:00:00.000Z');
assert.equal(u.toIsoString(-540), '1970-01-01T09:00:00.000+09:00');
assert.equal(u.toIsoString(-720), '1970-01-01T12:00:00.000+12:00');
assert.equal(u.toIsoString(720), '1969-12-31T12:00:00.000-12:00');
console.log(u.toIsoStringUtc());

u = Unixtime.fromMillis(0);
console.log(u.toIsoStringUtc());
u = Unixtime.fromMillis(-1);
console.log(u.toIsoStringUtc());

From date

let u = Unixtime.from(1969, 12, 31)
console.log(u.toIsoStringUtc());
console.log();

u = Unixtime.from(1969, 12, 30)
console.log(u.toIsoStringUtc());
console.log();

u = Unixtime.fromUtc(0, 1, 1);
assert.equal(u.timestamp, -62167219200000n)
assert.equal(u.getWeekShort(0), 'Sat')
console.log(u.toIsoStringUtc());
console.log();

u = Unixtime.fromUtc(-2, 12, 31, 23, 59, 59);
assert.equal(u.timestamp, -62198755201000n)
assert.equal(u.getWeekShort(0), 'Thu')
console.log(u.toIsoStringUtc());
console.log();

u = Unixtime.fromUtc(-4, 2, 29, 23, 59, 59);
assert.equal(u.timestamp, -62288265601000n)
assert.equal(u.getWeekShort(0), 'Thu')
console.log(u.toIsoStringUtc());
console.log();

u = Unixtime.fromUtc(-2000, 2, 29, 23, 59, 59);
assert.equal(u.timestamp, -125275939201000n)
assert.equal(u.getWeekShort(0), 'Tue')
console.log(u.toIsoStringUtc());
console.log();

u = Unixtime.fromUtc(-2000, 3, 1, 0, 0, 0);
assert.equal(u.timestamp, -125275939200000n)
assert.equal(u.getWeekShort(0), 'Wed')
console.log(u.toIsoStringUtc());
console.log();

Now

let u = Unixtime.now();
console.log('string', u.toString())
console.log('string', u.toString())
console.log('datetime', u.toDateTimeDetail())
console.log('time', u.timestamp)
assert.equal(u.toIsoStringUtc(), u.toIsoString(0));
console.log();

Format

let u = Unixtime.now();
u = Unixtime.now();
console.log(u.format(`yyyy yy MM dd HH hh mm ss SSS XXX a e EE E 'yyyy escape'`));
// 2026 2026 05 19 21 09 17 35 183 +09:00 PM 2 Tuesday Tue yyyy escape
console.log(u.format(`yyyy yy MM dd HH hh mm ss SSS XXX a e EE E 'yyyy escape'`, -60));
// 2026 2026 05 19 13 01 17 35 183 +01:00 PM 2 Tuesday Tue yyyy escape
console.log(u.formatUtc(`yyyy yy MM dd HH hh mm ss SSS XXX a e EE E 'yyyy escape'`));
// 2026 2026 05 19 12 12 17 35 183 Z PM 2 Tuesday Tue yyyy escape