@qntm-code/utils/dist/mjs/dates/modifiers/modify-date.js

A collection of useful utility functions with associated TypeScript types. All functions have been unit tested.

import { TimeUnit, unitToMS } from '../convert-units/index.js';
import { getEndOfMonth, getStartOfMonth } from '../getters/index.js';
/**
 * Modifies a date by a given amount of time units
 */
export function modifyDate(date, amount, unit) {
    let newDate = new Date(date);
    amount = Math.round(amount);
    const originalHour = date.getHours();
    switch (unit) {
        case TimeUnit.Millisecond:
        case TimeUnit.Milliseconds:
        case TimeUnit.Second:
        case TimeUnit.Seconds:
        case TimeUnit.Minute:
        case TimeUnit.Minutes:
        case TimeUnit.Hour:
        case TimeUnit.Hours: {
            newDate = new Date(newDate.getTime() + unitToMS(amount, unit));
            break;
        }
        case TimeUnit.Day:
        case TimeUnit.Days: {
            newDate.setDate(newDate.getDate() + amount);
            break;
        }
        case TimeUnit.Week:
        case TimeUnit.Weeks: {
            newDate.setDate(newDate.getDate() + amount * 7);
            break;
        }
        case TimeUnit.Month:
        case TimeUnit.Months:
        case TimeUnit.Year:
        case TimeUnit.Years: {
            newDate = getStartOfMonth(newDate);
            break;
        }
    }
    switch (unit) {
        case TimeUnit.Month:
        case TimeUnit.Months: {
            newDate.setMonth(newDate.getMonth() + amount);
            break;
        }
        case TimeUnit.Year:
        case TimeUnit.Years: {
            newDate.setFullYear(newDate.getFullYear() + amount);
            break;
        }
    }
    switch (unit) {
        case TimeUnit.Month:
        case TimeUnit.Months:
        case TimeUnit.Year:
        case TimeUnit.Years: {
            limitLastDayOfMonth(date, newDate);
            newDate.setHours(originalHour);
            break;
        }
    }
    return newDate;
}
function limitLastDayOfMonth(date, newDate) {
    const currentLastDay = date.getDate();
    const newDateLastDay = getEndOfMonth(newDate).getDate();
    if (currentLastDay > newDateLastDay) {
        newDate.setDate(newDateLastDay);
    }
    else {
        newDate.setDate(currentLastDay);
    }
}