check if a date is within dst

dst.ts

function isDST(date: Date, timeZone: string = 'America/New_York'): boolean {
    const year = date.getFullYear();
    const startDST = getNthDayOfMonth(2, 0, 2, year); // sec sun in mar
    const endDST = getNthDayOfMonth(1, 0, 10, year); // first sun in nov
    const localDate = new Date(date.toLocaleString('en-US', { timeZone }));
    const utcOffset = localDate.getTimezoneOffset() * 60000; // in milliseconds
    const utcDate = new Date(localDate.getTime() + utcOffset);

    return utcDate >= startDST && utcDate < endDST;
}

function getNthDayOfMonth(nth: number, day: number, month: number, year: number): Date {
    const date = new Date(year, month, 1);
    const add = (day - date.getDay() + 7) % 7 + (nth - 1) * 7;
    date.setDate(1 + add);
    return new Date(Date.UTC(year, month, date.getDate(), 2)); // 2am local time in UTC
}