Get unique and sequential week identifier for any date. Modern ES6+ with robust error handling.

Week #1 starts on January 5, 1970 (Monday). Each week runs Monday to Sunday.

Install

npm install week-identifier

# Test the installation
npm test

# Try the CLI
week-identifier --help

API

For comprehensive test examples see test.js and test-cli.js

weekIdentifier(date?)

Get sequential week identifier for any date

• date {string|Date} - Date string (any valid format) or Date object (optional, defaults to current date)
• returns {number} - Sequential week identifier (1-based)
• throws {Error} - When provided date is invalid

Examples:

const weekIdentifier = require('week-identifier');

// Current week (depends on today's date)
weekIdentifier();
//=> 2433

// Week 1 (epoch start)
weekIdentifier('January 5, 1970');
//=> 1

// Various date formats supported
weekIdentifier('January 12, 1970');
//=> 2

weekIdentifier(new Date('August 12, 2016'));
//=> 2432

weekIdentifier('08/12/2016');
//=> 2432

weekIdentifier('August 12, 2016');
//=> 2432

// Error handling for invalid dates
try {
  weekIdentifier('invalid date');
} catch (error) {
  console.error(error.message);
  //=> 'Invalid date string: "invalid date"'
}

weekIdentifier.dateFromWeek(weekId)

Convert week identifier back to its Monday date

• weekId {number|string} - Week identifier to convert
• returns {Date} - Monday date of the specified week
• throws {Error} - When weekId is not a valid number

Examples:

const weekIdentifier = require('week-identifier');

// Get Monday of week 2433
weekIdentifier.dateFromWeek(2433);
//=> Date object for August 15, 2016 00:00:00

// Week 1 returns epoch start
weekIdentifier.dateFromWeek(1);
//=> Date object for January 5, 1970 00:00:00

// Week 0 or negative returns epoch start
weekIdentifier.dateFromWeek(0);
//=> Date object for January 5, 1970 00:00:00

// Error handling
try {
  weekIdentifier.dateFromWeek('abc');
} catch (error) {
  console.error(error.message);
  //=> 'Invalid week identifier: "abc"'
}

CLI Usage

The package includes a powerful command-line interface with enhanced argument parsing.

Installation & Usage

# Install globally for CLI access
npm install -g week-identifier

# Or use without installing
npx week-identifier

Commands & Options

# Get current week identifier
week-identifier
#=> 2433

# Get week identifier for specific dates  
week-identifier "January 5, 1970"
#=> 1

week-identifier "August 12, 2016"  
#=> 2432

week-identifier "02/17/2012"
#=> 2198

# Convert week identifier back to date
week-identifier --from 2432
#=> 2016-08-08

week-identifier --from 1
#=> 1970-01-05

# Get help and version info
week-identifier --help
week-identifier --version

Error Handling

# Invalid date strings show helpful errors
week-identifier "invalid date"
#=> Error: Invalid date string: "invalid date"
#=> Use --help for usage information.

# Invalid week identifiers are caught
week-identifier --from abc  
#=> Error: Invalid week identifier: "abc"
#=> Use --help for usage information.

License

Copyright (c) 2025 [Clément Billiot], contributors.
Released under the MIT license.