Add Theme and Gradient Support to Chalk

Overview

This PR introduces two powerful new features to Chalk: custom themes and color gradients, enabling more flexible and sophisticated terminal styling capabilities.

Features

🎨 Themes

Create themed Chalk instances with custom style definitions for consistent coloring throughout your application.

const themedChalk = chalk.theme({
  error: chalk.bold.red,
  success: chalk.green,
  warning: chalk.hex('#FFA500'),
  info: chalk.blue,
  title: chalk.cyan.bold.underline,
});

console.log(themedChalk.error('Error!'));
console.log(themedChalk.success('Success!'));

Benefits:

• Define application-wide style conventions in one place
• Ensure consistent coloring across your CLI
• Reusable theme definitions

🌈 Gradients

Apply smooth color gradients to text with support for multiple color formats.

// Hex colors
chalk.gradient('#ff0000', '#0000ff')('Hello World')

// RGB arrays
chalk.gradient([255, 0, 0], [0, 255, 0], [0, 0, 255])('Rainbow')

// Multiple colors
chalk.gradient('#ff0000', '#ffff00', '#00ff00', '#00ffff', '#0000ff')('Spectrum')

Features:

• Supports hex string and RGB array color formats
• Works with all Chalk modifiers (bold, underline, etc.)
• Compatible with themed instances
• Respects color support level (16, 256, or 16M colors)

Changes

Documentation

• readme.md: Added comprehensive sections for themes and gradients with usage examples

Type Definitions

• source/index.d.ts: Added TypeScript definitions for theme() and gradient() methods

Implementation

• source/index.js:

  • Implemented theme() method to create themed instances
  • Implemented gradient() method with proper style chain handling
  • Enhanced applyStyle() to support gradient rendering

• source/utilities.js:

  • Added interpolateRgb() for color interpolation
  • Added createGradientStyler() to create gradient styler objects
  • Added applyGradient() to render gradients with proper ANSI code generation

Compatibility

• ✅ Works with all existing Chalk features
• ✅ Respects color support detection
• ✅ No breaking changes to existing API
• ✅ Supports chaining with other styles

Testing

Recommended test coverage:

• Theme creation and property access
• Gradient rendering with 2+ colors
• Gradient + style combinations
• Color level adaptation (16, 256, 16M)
• Edge cases (empty strings, single character, etc.)

Type of change: ✨ New feature

Fixes #666