misskey/packages/client/src/scripts/time.ts

const dateTimeIntervals = {
	'day': 86400000,
	'hour': 3600000,
	'ms': 1,
};

export function dateUTC(time: number[]): Date {
	const d = time.length === 2 ? Date.UTC(time[0], time[1])
					: time.length === 3 ? Date.UTC(time[0], time[1], time[2])
					: time.length === 4 ? Date.UTC(time[0], time[1], time[2], time[3])
					: time.length === 5 ? Date.UTC(time[0], time[1], time[2], time[3], time[4])
					: time.length === 6 ? Date.UTC(time[0], time[1], time[2], time[3], time[4], time[5])
					: time.length === 7 ? Date.UTC(time[0], time[1], time[2], time[3], time[4], time[5], time[6])
					: null;

	if (!d) throw 'wrong number of arguments';

	return new Date(d);
}

export function isTimeSame(a: Date, b: Date): boolean {
	return a.getTime() === b.getTime();
}

export function isTimeBefore(a: Date, b: Date): boolean {
	return (a.getTime() - b.getTime()) < 0;
}

export function isTimeAfter(a: Date, b: Date): boolean {
	return (a.getTime() - b.getTime()) > 0;
}

export function addTime(x: Date, value: number, span: keyof typeof dateTimeIntervals = 'ms'): Date {
	return new Date(x.getTime() + (value * dateTimeIntervals[span]));
}

export function subtractTime(x: Date, value: number, span: keyof typeof dateTimeIntervals = 'ms'): Date {
	return new Date(x.getTime() - (value * dateTimeIntervals[span]));
}