Is Lower Case

Check if a string is in lowercase format.

🚀 Features

• Lightweight - Only ~200B minified + gzipped
• Type-safe - Full TypeScript support with comprehensive type definitions
• Zero dependencies - No external dependencies
• Tree-shakeable - ES modules support
• Universal - Works in browsers, Node.js, and serverless environments
• Well-tested - Comprehensive test suite with edge cases

📦 Installation

# npm
npm install text-is-lower-case

# yarn
yarn add text-is-lower-case

# pnpm
pnpm add text-is-lower-case

# bun
bun add text-is-lower-case

🎯 Quick Start

import { isLowerCase } from "text-is-lower-case";

console.log(isLowerCase("hello world")); // true
console.log(isLowerCase("Hello World")); // false
console.log(isLowerCase("HELLO WORLD")); // false

📖 Usage

ES Modules (Recommended)

import { isLowerCase } from "text-is-lower-case";

console.log(isLowerCase("hello")); // true

CommonJS

const { isLowerCase } = require("text-is-lower-case");

console.log(isLowerCase("hello")); // true

TypeScript

import { isLowerCase } from "text-is-lower-case";

const result: boolean = isLowerCase("hello world");
console.log(result); // true

🔄 Validation Examples

Basic Validation

import { isLowerCase } from "text-is-lower-case";

// Valid lowercase
isLowerCase("hello"); // true
isLowerCase("hello world"); // true
isLowerCase("test123"); // true
isLowerCase("user_name"); // true
isLowerCase("api-key"); // true

// Invalid (not lowercase)
isLowerCase("Hello"); // false
isLowerCase("HELLO"); // false
isLowerCase("Hello World"); // false
isLowerCase("camelCase"); // false
isLowerCase("PascalCase"); // false

Edge Cases

import { isLowerCase } from "text-is-lower-case";

// Numbers and symbols
isLowerCase("123"); // true
isLowerCase("hello123"); // true
isLowerCase("test@email.com"); // true
isLowerCase("user_123"); // true

// Empty and whitespace
isLowerCase(""); // true
isLowerCase("   "); // true
isLowerCase("\n\t"); // true

// Special characters
isLowerCase("hello-world"); // true
isLowerCase("test_case"); // true
isLowerCase("file.txt"); // true

🌍 Real-World Examples

Form Validation

import { isLowerCase } from "text-is-lower-case";

function validateUsername(username) {
  if (!isLowerCase(username)) {
    return "Username must be lowercase";
  }
  return null;
}

console.log(validateUsername("john_doe")); // null (valid)
console.log(validateUsername("John_Doe")); // "Username must be lowercase"

Email Validation

import { isLowerCase } from "text-is-lower-case";

function validateEmailFormat(email) {
  const [localPart] = email.split("@");

  if (!isLowerCase(localPart)) {
    return "Email local part should be lowercase";
  }
  return null;
}

console.log(validateEmailFormat("user@example.com")); // null
console.log(validateEmailFormat("User@example.com")); // "Email local part should be lowercase"

URL Slug Validation

import { isLowerCase } from "text-is-lower-case";

function validateSlug(slug) {
  if (!isLowerCase(slug)) {
    return "URL slug must be lowercase";
  }
  return null;
}

console.log(validateSlug("my-blog-post")); // null
console.log(validateSlug("My-Blog-Post")); // "URL slug must be lowercase"

Configuration Validation

import { isLowerCase } from "text-is-lower-case";

function validateConfigKeys(config) {
  const invalidKeys = Object.keys(config).filter((key) => !isLowerCase(key));

  if (invalidKeys.length > 0) {
    return `Invalid config keys (must be lowercase): ${invalidKeys.join(", ")}`;
  }
  return null;
}

const config1 = { database_url: "...", api_key: "..." };
const config2 = { databaseUrl: "...", apiKey: "..." };

console.log(validateConfigKeys(config1)); // null
console.log(validateConfigKeys(config2)); // "Invalid config keys..."

📖 API Reference

isLowerCase(input)

Checks if a string is in lowercase format.

Parameters

• input (string): The string to check

Returns

• boolean: true if the string is lowercase, false otherwise

📊 Bundle Size

This package is optimized for minimal bundle size:

• Minified: ~200B
• Gzipped: ~150B
• Tree-shakeable: Yes
• Side effects: None

🌍 Browser Support

• Modern browsers: ES2015+ (Chrome 51+, Firefox 54+, Safari 10+)
• Node.js: 12+
• TypeScript: 4.0+
• Bundle formats: UMD, ESM, CommonJS

🧪 Testing

# Run tests
pnpm test

# Run tests in watch mode
pnpm test --watch

# Run tests with coverage
pnpm test --coverage

# Type checking
pnpm typecheck

# Linting
pnpm lint

🔗 Related Packages

• text-is-upper-case - Check if string is uppercase
• text-lower-case - Convert to lowercase
• text-upper-case - Convert to uppercase
• text-case - All case transformations in one package

📜 License

MIT © Dmitry Selikhov

🤝 Contributing

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

🆘 Support

• 📧 Email: selikhov.dmitrey@gmail.com
• 🐛 Issues: GitHub Issues
• 💬 Discussions: GitHub Discussions
• 📖 Documentation: Full Documentation

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Made with ❤️ by Dmitry Selikhov