ts-function-similarity

TypeScript Function Similarity Analyzer

A tool that recursively extracts TypeScript functions from a directory, parses them using the TypeScript AST parser, and compares them using Levenshtein distance to calculate similarity scores.

Features

• Recursively scans directories for TypeScript files (.ts, .tsx)
• Supports multiple directories and individual files
• Extracts all function declarations, expressions, arrow functions, and methods
• Parses functions using @typescript-eslint/typescript-estree
• Calculates similarity scores using Levenshtein distance algorithm
• Normalizes code (removes comments and whitespace) for better comparison
• CLI tool with various options
• Real-time progress indicator for large codebases
• Memory optimizations:
  • Pre-caches normalized code to avoid repeated normalization
  • Early filtering based on length differences
  • Increased heap size (8GB) for large codebases
  • Progressive memory cleanup during comparison

Installation

From npm (recommended after publishing)

npm install -g ts-function-similarity
# Now you can use 'ts-similarity' command anywhere
ts-similarity ./src --min 70

From source

cd ts-function-similarity
npm install
npm run build

# Optional: Link globally
npm link
ts-similarity ./src --min 70

Usage

Command Line

# Analyze current directory
npm start

# Analyze specific directory
npm start ./src

# Analyze multiple directories
npm start ./src ./lib ./utils

# Analyze specific files
npm start src/file1.ts src/file2.ts

# Mix directories and files
npm start ./src file.ts

# Using --dir flag (can be used multiple times)
npm start -- -d ./src -d ./lib --min 70

# Show only functions with 70%+ similarity
npm start -- --min 70

# Find potential duplicates (90%+ similarity)
npm start -- --duplicates

# Limit results to top 10
npm start -- --limit 10

CLI Options

• -d, --dir <path> - Directory or file to analyze (can be used multiple times, default: current directory)
• -m, --min <number> - Minimum similarity score to display (0-100, default: 50)
• --min-lines <number> - Minimum number of lines for functions to compare (default: 0, no filter)
• -l, --limit <number> - Maximum number of results to display (default: 20)
• --duplicates - Only show potential duplicates (similarity >= 90%)
• -h, --help - Show help message

Multiple Directories and Files

The tool supports analyzing multiple directories and files in a single run. This is useful for:

• Cross-module comparison: Compare functions across different parts of your codebase

  npm start ./src/components ./src/services ./src/utils
  

• Monorepo analysis: Compare functions across multiple packages

  npm start ./packages/core ./packages/ui ./packages/api
  

• Specific file comparison: Compare only certain files

  npm start src/auth.ts src/user.ts lib/helpers.ts
  

• Mixed analysis: Combine directories and files

  npm start ./src specific-file.ts
  

Output example:

Analyzing TypeScript files in 3 directories:

  1. ./src/components
  2. ./src/services
  3. ./src/utils

Extracting functions...
  ./src/components: found 342 functions
  ./src/services: found 189 functions
  ./src/utils: found 127 functions

Total: 658 functions

Programmatic Usage

import { FunctionExtractor } from './functionExtractor';
import { FunctionComparator } from './comparator';

// Extract functions from multiple directories
const extractor = new FunctionExtractor();
const functions1 = await extractor.extractFromDirectory('./src');
const functions2 = await extractor.extractFromDirectory('./lib');
const allFunctions = [...functions1, ...functions2];

// Compare all functions
const comparator = new FunctionComparator();
const results = comparator.compareAll(allFunctions, {
  minSimilarity: 50,
  normalize: true,
  excludeSelf: true,
});

// Find duplicates
const duplicates = comparator.findDuplicates(allFunctions, 90);

How It Works

• Extraction: The tool recursively scans the specified directory for TypeScript files
• Parsing: Each file is parsed into an AST using @typescript-eslint/typescript-estree
• Function Detection: The AST is traversed to find all function nodes:
  • Function declarations
  • Function expressions
  • Arrow functions
  • Method definitions
• Comparison: Functions are compared pairwise using Levenshtein distance
• Normalization: Code is normalized by removing comments and whitespace for better comparison
• Scoring: Similarity scores are calculated as a percentage (0-100%)

Levenshtein Distance

The Levenshtein distance measures the minimum number of single-character edits (insertions, deletions, or substitutions) needed to transform one string into another. This tool converts that distance into a similarity percentage:

similarity = ((max_length - distance) / max_length) × 100

Output

The tool displays:

• Number of functions found
• Number of similar pairs
• For each pair:
  • Similarity score (normalized and raw)
  • Function names
  • File locations with line numbers

Example Output

Analyzing TypeScript files in: src

Extracting functions...
Found 1204 functions

Comparing functions (724,806 comparisons)...
Progress: 25% (181,201/724,806)
Progress: 50% (362,403/724,806)
Progress: 75% (543,604/724,806)
Progress: 100% (724,806/724,806)


Found 10 similar function pairs

================================================================================

1. Similarity: 85.32% (Raw: 78.45%)
   Function 1: calculateTotal (11 lines)
   Location:   src/utils/math.ts:15-25
   Function 2: computeSum (11 lines)
   Location:   src/helpers/calculator.ts:42-52

================================================================================

Filtering by Function Size

The --min-lines option allows you to focus on substantial code blocks and ignore small utility functions that might coincidentally match.

Why Use --min-lines?

Problem: Small functions (2-3 lines) often have high similarity scores but aren't meaningful duplicates:

// These might show 100% similarity but aren't really duplicates
const add = (a, b) => a + b;
const sum = (x, y) => x + y;

Solution: Use --min-lines to filter out small functions and prioritize larger code blocks:

# Only compare functions with 10 or more lines
npm start -- ./src --min-lines 10

# Find duplicates in substantial functions (15+ lines)
npm start -- ./src --duplicates --min-lines 15

# Focus on larger functions with high similarity
npm start -- ./src --min 80 --min-lines 20

Benefits

• Reduces noise: Eliminates trivial matches like simple getters/setters
• Finds meaningful duplicates: Focuses on substantial code that's worth refactoring
• Massive performance boost: Pre-filters functions before comparison, dramatically reducing comparisons
• Better results: Prioritizes functions where duplication actually matters

Performance Impact

The --min-lines filter provides dramatic performance improvements by pre-filtering functions before comparison:

$ npm start -- ./src --min-lines 10

# Example with 1204 functions:
# Without filter: 724,806 comparisons
# With --min-lines 10 (500 functions): 124,750 comparisons (83% reduction)
# With --min-lines 20 (200 functions): 19,900 comparisons (97% reduction)

Real-world example:

Filtering: 7 functions meet minimum 4 lines (5 filtered out)
Performance: 21 comparisons instead of 66 (68% reduction)

Example Output

$ npm start -- ./src --min 70 --min-lines 10

# Without --min-lines: 150 results (many 2-3 line functions)
# With --min-lines 10: 23 results (only substantial functions)

Recommended Values

• 10 lines: Good default for filtering trivial functions
• 15 lines: Focus on medium-to-large functions
• 20+ lines: Only compare substantial code blocks
• 5 lines: Light filtering, keeps most functions

Project Structure

ts-function-similarity/
├── src/
│   ├── index.ts              # CLI entry point
│   ├── functionExtractor.ts  # AST parsing and function extraction
│   ├── levenshtein.ts        # Levenshtein distance algorithm
│   └── comparator.ts         # Function comparison logic
├── package.json
├── tsconfig.json
└── README.md

Performance Tips

For Large Codebases (1000+ functions)

When analyzing large codebases, consider these optimization strategies:

• Use a higher similarity threshold: Set --min 80 or --min 90 to filter out most comparisons early

  npm start -- ./src --min 90
  

• Use duplicates mode: This automatically sets the threshold to 90%

  npm start -- ./src --duplicates
  

• Memory usage: The tool is configured with 8GB heap size by default. For very large codebases (2000+ functions), you may need more:

  node --max-old-space-size=16384 dist/index.js ./src --min 90
  

• Complexity: With N functions, the tool performs N×(N-1)/2 comparisons:

  • 100 functions = 4,950 comparisons
  • 500 functions = 124,750 comparisons
  • 1,000 functions = 499,500 comparisons
  • 1,500 functions = 1,124,250 comparisons
  • 2,000 functions = 1,999,000 comparisons

Use Cases

• Find duplicate or near-duplicate functions in a codebase
• Identify refactoring opportunities
• Detect copy-pasted code
• Code review assistance
• Technical debt analysis

MCP Server

This package includes an MCP (Model Context Protocol) server that allows AI assistants like Claude to analyze your TypeScript code for function similarity.

See MCP.md for detailed setup instructions and usage examples.

Quick setup for Claude Desktop:

• Install the package globally: npm install -g ts-function-similarity
• Add to your Claude Desktop config (~/Library/Application Support/Claude/claude_desktop_config.json):

  {
    "mcpServers": {
      "ts-function-similarity": {
        "command": "ts-similarity-mcp"
      }
    }
  }
  

• Restart Claude Desktop
• Ask Claude to analyze your TypeScript code for similarities!

License

MIT - See LICENSE file for details