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subtract()

Calculates the difference between two Date objects and returns a rich Duration object with multiple time units and formatting options.

Syntax

subtract(date1, date2)

Parameters

Parameter Type Required Description
date1 Date Yes The earlier/start date
date2 Date Yes The later/end date

Returns

Duration - Rich duration object containing the time difference with properties for years, months, days, hours, minutes, seconds, and milliseconds

Basic Examples

Calculating Time Differences

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

const start = new Date(2024, 0, 1, 10, 30, 0);  // January 1, 2024 10:30:00
const end = new Date(2024, 0, 1, 14, 45, 30);   // January 1, 2024 14:45:30

const duration = subtract(start, end);

console.log(duration.toHours().value);    // 4.258333...
console.log(duration.toMinutes().value);  // 255.5
console.log(duration.toSeconds().value);  // 15330

const hoursParts = duration.toHours().toParts();

console.log(hoursParts.hours);    // 4
console.log(hoursParts.minutes);  // 15
console.log(hoursParts.seconds);  // 30

Cross-Day Calculation

const start = new Date(2024, 6, 15, 22, 30); // July 15, 2024 22:30
const end = new Date(2024, 6, 18, 8, 15);     // July 18, 2024 08:15

const duration = subtract(start, end);
const daysParts = duration.toDays().toParts();

console.log(daysParts.days);     // 2
console.log(daysParts.hours);    // 9
console.log(daysParts.minutes);  // 45
console.log(duration.toHours().value); // 57.75 (total hours as decimal)

Age Calculation

const birthDate = new Date(1990, 5, 15); // June 15, 1990
const today = new Date(); // Current date

const age = subtract(birthDate, today);
const ageParts = age.toDays().toParts();

// Note: Simple age calculation (not accounting for leap years)
console.log(`Age: ${Math.floor(ageParts.days / 365)} years`);

// Get total days lived
console.log(`Total days lived: ${ageParts.days}`);

Duration Object Methods

The returned Duration object provides methods to convert and format durations. The Duration can also be directly instantiated with a millisecond value:

class Duration {
  constructor(milliseconds: number)  // Create Duration instance directly
  
  // Convert to different time units with value and formatting capabilities
  toNanoseconds(): DurationDescriptor<NanosecondsParts>
  toMicroseconds(): DurationDescriptor<MicrosecondsParts>
  toMilliseconds(): DurationDescriptor<MillisecondsParts>
  toSeconds(): DurationDescriptor<SecondsParts>
  toMinutes(): DurationDescriptor<MinutesParts>
  toHours(): DurationDescriptor<HoursParts>
  toDays(): DurationDescriptor<DaysParts>
}

interface DurationDescriptor<T> {
  value: number                                        // Total duration in the specified unit
  format: (formatString: string, numeral?: Numeral) => string  // Format duration with custom pattern
  toParts: () => T                                     // Get duration broken down into parts
}

// Example part interfaces
interface HoursParts {
  hours: number
  minutes: number
  seconds: number
  milliseconds: number
  microseconds: number
  nanoseconds: number
}

Creating Duration Instances Directly

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

// Create a Duration for 2 hours (7200000 milliseconds)
const duration = new Duration(7200000);
console.log(duration.toHours().value);     // 2
console.log(duration.toMinutes().value);   // 120

// Format the duration
console.log(duration.toHours().format('H[h] m[m]'));  // "2h 0m"

Advanced Duration Formatting

const start = new Date(2024, 7, 15, 9, 30, 45);
const end = new Date(2024, 7, 18, 16, 15, 20);
const duration = subtract(start, end);

// Various formatting options
console.log(duration.toDays().format('D[d] H[h] m[m]'));          // "3d 6h 44m"
console.log(duration.toHours().format('H:mm:ss'));                // "78:44:35"
console.log(duration.toMinutes().format('[Total minutes:] m'));   // "Total minutes: 4724"
console.log(duration.toDays().format('D[day], H:mm:ss.SSS'));     // "3day, 6:44:35.000"

Use Cases

Work Session Tracking

const clockIn = new Date(2024, 7, 15, 9, 0);   // August 15, 2024 09:00
const clockOut = new Date(2024, 7, 15, 17, 45); // August 15, 2024 17:45

const duration = subtract(clockIn, clockOut);
console.log(duration.toHours().value);           // 8.75
console.log(duration.toHours().format('H:mm'));  // "8:45"
console.log(duration.toHours().format('H[h] m[m]'));  // "8h 45m"

Performance Monitoring

const start = performance.now();
// ... some operation ...
const end = performance.now();

// Create Duration directly from millisecond difference
const duration = new Duration(end - start);

console.log(duration.toMilliseconds().format('SSS[ms]'));  // "234ms"

Edge Cases and Behavior

Negative Durations

When the first argument is later than the second argument, subtract() returns negative duration values. This behavior allows for flexible date comparison in either direction.

// Comparing dates in reverse chronological order
const later = new Date(2024, 7, 15, 14, 30);    // 2:30 PM
const earlier = new Date(2024, 7, 15, 10, 15);  // 10:15 AM

const negativeDuration = subtract(later, earlier);
console.log(negativeDuration.toHours().value);    // -4.25 (negative value)
console.log(negativeDuration.toMinutes().value);  // -255 (all values are negative)

// Format methods handle negative values appropriately
console.log(negativeDuration.toHours().format('H[h] m[m]'));  // "-4h 15m"

Negative Zero

An edge case of negative durations occurs when the difference is negative but the integer part of certain units is zero. This affects both toParts() and format() output differently.

// Short negative duration (less than 1 day but more than 1 hour)
const date1 = new Date(2024, 7, 15, 14, 30);  // 2:30 PM
const date2 = new Date(2024, 7, 15, 12, 15);  // 12:15 PM

const duration = subtract(date1, date2);
console.log(duration.toDays().value);   // -0.09375 (negative but less than 1 day)

// toParts() shows negative signs on all non-zero unit values
const parts = duration.toDays().toParts();
console.log(parts);  // { days: 0, hours: -2, minutes: -15, seconds: 0, ... }

// format() places a single negative sign at the beginning, potentially creating "-0"
console.log(duration.toDays().format('D[day], H:mm:ss'));  // "-0day, 2:15:00"

Immutability

Both input Date objects remain unchanged:

const date1 = new Date(2024, 7, 15, 14, 30);
const date2 = new Date(2024, 7, 15, 12, 15);
const duration = subtract(date2, date1);

console.log(date1); // Unchanged
console.log(date2); // Unchanged
console.log(duration.toHours().value);  // 2.25 (new Duration object)

See Also