string-incr

Increment or decrement strings with numbers

A lightweight, zero-dependency utility for incrementing and decrementing strings that contain numbers. Perfect for generating sequential names, slugs, or identifiers.

Features

• 🚀 Zero dependencies
• 📦 Dual ESM/CommonJS support
• 🔒 Fully typed with TypeScript
• ✅ Comprehensive test coverage
• 🪶 Lightweight (~1KB minified)

Installation

npm install string-incr
# or
yarn add string-incr
# or
pnpm add string-incr

Usage

ESM

import { stringIncr, stringDecr } from 'string-incr'

stringIncr('Hello world 42')
//=> 'Hello world 43'

stringIncr('Hello world')
//=> 'Hello world 1'

stringDecr('Hello world 42')
//=> 'Hello world 41'

stringDecr('Hello world 1')
//=> 'Hello world'

CommonJS

const { stringIncr, stringDecr } = require('string-incr')

stringIncr('Hello world 42')
//=> 'Hello world 43'

stringDecr('Hello world 2')
//=> 'Hello world 1'

stringDecr('Hello world 1')
//=> 'Hello world'

API

stringIncr(str, firstAppend?)

Increments a string that ends with a number, or appends a number if none exists.

Parameters

• str (string | number): The string or number to increment
• firstAppend (string | number, optional): The separator/number to use when no number exists (default: ' 1')

Returns

• string: The incremented string

Examples

// Basic increment
stringIncr('Hello world')
//=> 'Hello world 1'

stringIncr('Hello world 1')
//=> 'Hello world 2'

stringIncr('Hello world 2')
//=> 'Hello world 3'

stringIncr('Hello world 42')
//=> 'Hello world 43'

// Numbers without spaces
stringIncr('Hello world42')
//=> 'Hello world43'

stringIncr('Hello 42 world99')
//=> 'Hello 42 world100'

// With separators
stringIncr('Hello world-42')
//=> 'Hello world-43'

// Custom first append
stringIncr('Hello world', '-1')
//=> 'Hello world-1'

stringIncr('Hello world', '#42')
//=> 'Hello world#42'

stringIncr('Hello world', 42)
//=> 'Hello world 42'

stringIncr('Hello world', 1)
//=> 'Hello world 1'

stringIncr('Hello world', '#')
//=> 'Hello world#1'

// Number input
stringIncr(41)
//=> '42'

// Edge cases
stringIncr('')
//=> '1'

stringDecr(str, removeSeparator?)

Decrements a string that ends with a number. When the number reaches 1 or 0, it removes the number entirely.

Parameters

• str (string | number): The string or number to decrement
• removeSeparator (string, optional): Separator to remove when number reaches ≤ 1 (only applied at 1 or 0, not during normal decrements)

Returns

• string: The decremented string, or the base string when number reaches ≤ 1

Examples

// Basic decrement
stringDecr('Hello world 42')
//=> 'Hello world 41'

stringDecr('Hello world 3')
//=> 'Hello world 2'

stringDecr('Hello world 2')
//=> 'Hello world 1'

// Removes number when reaching 1 or 0
stringDecr('Hello world 1')
//=> 'Hello world'

stringDecr('Hello world 0')
//=> 'Hello world'

// No change when no number exists
stringDecr('Hello world')
//=> 'Hello world'

// Numbers without spaces
stringDecr('Hello world42')
//=> 'Hello world41'

stringDecr('Hello 42 world100')
//=> 'Hello 42 world99'

// With separators - keeps separator by default
stringDecr('Hello world-42')
//=> 'Hello world-41'

stringDecr('Hello world-1')
//=> 'Hello world-'

// With separators - remove separator when specified
stringDecr('Hello world-1', '-')
//=> 'Hello world'

stringDecr('Hello world#1', '#')
//=> 'Hello world'

stringDecr('Hello_world_1', '_')
//=> 'Hello_world'

// removeSeparator ONLY applies when number reaches 1 or 0
stringDecr('Hello world-42', '-')
//=> 'Hello world-41'  ← separator NOT removed (number > 1)

stringDecr('Hello world-2', '-')
//=> 'Hello world-1'  ← separator NOT removed (number > 1)

stringDecr('Hello world-1', '-')
//=> 'Hello world'  ← separator removed (number = 1)

// Number input (mathematical operation)
stringDecr(42)
//=> '41'

stringDecr(0)
//=> '-1'

Behavior

stringIncr

• Increments the last number in the string
• If no number exists, appends a default number (default: ' 1')
• The firstAppend parameter controls what to append when no number exists
• Numbers can be with or without spaces/separators

stringDecr

• Decrements the last number in the string
• When the number reaches 1 or 0, it removes the number entirely
• If no number exists, returns the string unchanged
• Numbers can be with or without spaces/separators

Important Notes

• Only trailing digits are extracted, not minus signs
  • stringIncr('test-5') → 'test-6' (the - is a separator, not part of the number)
  • stringDecr('test-5') → 'test-4' (extracts 5, decrements to 4)
  • stringDecr('test-1') → 'test-' (removes the 1)
• For mathematical operations on negative numbers, use number input:
  • stringIncr(-5) → '-4'
  • stringDecr(-5) → '-6'

See BEHAVIOR.md for detailed edge cases and design decisions.

Use Cases

• Generating sequential file names: file.txt → file 1.txt → file 2.txt
• Creating unique slugs: my-post → my-post 1 → my-post 2 (or use stringIncr('my-post', '-1') for my-post-1)
• Versioning identifiers: version-1 → version-2
• Duplicate name handling in any system
• Countdown sequences: item-5 → item-4 → item-3 → item-2 → item-1 → item

TypeScript

This package is written in TypeScript and includes type definitions out of the box.

import { stringIncr, stringDecr } from 'string-incr'

// Full type safety
const result: string = stringIncr('test 1')

Development

# Install dependencies
pnpm install

# Run tests
pnpm test

# Run tests in watch mode
pnpm test:watch

# Run tests with coverage
pnpm test:coverage

# Build
pnpm build

# Lint
pnpm lint

# Type check
pnpm typecheck

Changelog

Version 4.0.0 adds dual ESM/CommonJS support with breaking changes to default behavior. See CHANGELOG.md for full details and migration guide.

License

MIT © apoutchika

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

1. Fork the repository
2. Create your feature branch (git checkout -b feature/amazing-feature)
3. Commit your changes (git commit -m 'Add some amazing feature')
4. Push to the branch (git push origin feature/amazing-feature)
5. Open a Pull Request