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addHours()

Adds or subtracts hours from a Date object.

Syntax

addHours(dateObj, hours)

Parameters

ParameterTypeRequiredDescription
dateObjDateYesThe base Date object
hoursnumberYesNumber of hours to add (positive) or subtract (negative)

Returns

Date - A new Date object with the specified number of hours added or subtracted

Basic Examples

Adding and Subtracting Hours

import { addHours } from 'date-and-time';


const date = new Date(2024, 7, 15, 14, 30, 45); // August 15, 2024 14:30:45


// Add hours
const future = addHours(date, 6);
console.log(future);  // August 15, 2024 20:30:45


// Subtract hours
const past = addHours(date, -3);
console.log(past);  // August 15, 2024 11:30:45

Use Cases

Work Hours Calculation

function addWorkingHours(startDate: Date, workHours: number): Date {
  // Assuming 8-hour work days, 5 days a week
  const hoursPerDay = 8;
  const result = new Date(startDate);
  let remainingHours = workHours;


  while (remainingHours > 0) {
    const dayOfWeek = result.getDay();


    // Skip weekends
    if (dayOfWeek === 0 || dayOfWeek === 6) {
      result.setDate(result.getDate() + 1);
      continue;
    }


    const hoursToAdd = Math.min(remainingHours, hoursPerDay);
    const newTime = addHours(result, hoursToAdd);
    result.setTime(newTime.getTime());
    remainingHours -= hoursToAdd;


    if (remainingHours > 0) {
      // Move to next day, reset to start of work day
      result.setDate(result.getDate() + 1);
      result.setHours(9, 0, 0, 0); // 9 AM start
    }
  }


  return result;
}


const projectStart = new Date(2024, 7, 15, 9, 0); // August 15, 2024 09:00
const completion = addWorkingHours(projectStart, 24); // 24 working hours
console.log(completion);

Shift Scheduling

function generateShiftSchedule(startDate: Date, shiftHours: number, numberOfShifts: number): Date[] {
  const shifts: Date[] = [];
  let currentStart = new Date(startDate);


  for (let i = 0; i < numberOfShifts; i++) {
    shifts.push(new Date(currentStart));
    currentStart = addHours(currentStart, shiftHours);
  }


  return shifts;
}


const firstShift = new Date(2024, 7, 15, 6, 0); // August 15, 2024 06:00
const schedule = generateShiftSchedule(firstShift, 8, 5); // 5 shifts of 8 hours each
console.log(schedule);
// [
//   August 15, 2024 06:00,  // Shift 1
//   August 15, 2024 14:00,  // Shift 2
//   August 15, 2024 22:00,  // Shift 3
//   August 16, 2024 06:00,  // Shift 4
//   August 16, 2024 14:00   // Shift 5
// ]

Immutability

addHours() does not modify the original Date object:

const originalDate = new Date(2024, 7, 15, 14, 30);
const modifiedDate = addHours(originalDate, 5);


console.log(originalDate); // August 15, 2024 14:30:00 (unchanged)
console.log(modifiedDate); // August 15, 2024 19:30:00 (new object)

See Also