ast-logic-hasher

Ensure code logic remains unchanged during refactoring (Prettier, ESLint, etc.) by comparing AST hashes.

Why this?

When you format legacy code, git diff often becomes huge and noisy. This tool generates a SHA-1 hash of the code's logic structure (AST), ignoring formatting, comments, and metadata. If the hash remains the same, your refactoring hasn't changed the program's behavior.

Usage

Direct use with npx

# Direct use with npx
cat old.js | npx ast-logic-hasher > before.txt
cat new.js | npx ast-logic-hasher > after.txt
diff before.txt after.txt

Bulk verification (Recursive)

Perfect for verifying a large refactor across a whole project:

# 1. Before refactoring
find ./src -name "*.js" | sort | xargs -I {} sh -c 'echo -n "{}: "; cat {} | npx ast-logic-hasher' > before.txt

# ... do your refactoring (prettier, eslint --fix, etc.) ...

# 2. After refactoring
find ./src -name "*.js" | sort | xargs -I {} sh -c 'echo -n "{}: "; cat {} | npx ast-logic-hasher' > after.txt

# 3. Compare
diff before.txt after.txt

exmaple before.txt

./src/auth.js: d6fc3e9bc82506ecb2b8b8c28f85080570d639ae
./src/utils/api.js: 6b432b9eeaf3f3fd2ee1850fc40faf645f2199e0
./src/xxx/c.js: f013360319ad047c62c2411f9b505662d9f43e9f

Features

• Logic Only: Ignores comments, location data, and formatting.
• Modern JS Support: Supports JSX and TypeScript syntax out of the box.
• Deterministic: Object keys in AST are sorted before hashing to ensure consistency.

Requirements

• Node.js >= 20.0.0