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addHours.md

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addHours()

Adds or subtracts hours from a Date object.

Syntax

addHours(dateObj, hours)

Parameters

Parameter Type Required Description
dateObj Date Yes The base Date object
hours number Yes Number 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