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Project

This project contains TypeScript jscodeshift codemod examples.

Folder Structure

  • src: Contains the codemods and their tests.
  • src/simple-rename.ts: Example codemod that renames a variable.
  • src/simple-rename.spec.ts: Tests for the simple-rename codemod.

Dependencies

  • Use npm as the package manager.
  • Use jscodeshift for code transformations.
  • Use #context7-mcp to find jscodeshift documentation.
  • Use outdent for formatting multiline strings in tests.
  • Use Vitest for testing the transformations.
  • Do NOT install dependencies.

Writing Transformations

  • Use jscodeshift with TypeScript parser (parser: 'ts') for all transformations.
  • Create new jscodeshift transformations in the src folder.
  • Use simple-rename.ts and simple-rename.spec.ts as a template for writing new transformations.
  • Always export parser as export const parser: TestOptions['parser'] = 'ts'; to ensure TypeScript parsing.
  • Fix all TypeScript Type errors.
  • Use Type Narrowing if necessary to ensure type safety.
  • Set jscodeshift's .toSource() options to match the code style of the examples
  • Use explicit return file.source; when no transformation is needed, instead of using toSource().

Abstract Syntax Tree (AST)

  • Use jscodeshift API to traverse and manipulate the AST.
  • Use TypeScript ESTree node types (e.g., VariableDeclaration, Identifier) instead of generic AST types to access nodes.
  • Access TypeScript-specific nodes like interfaces, type aliases, and decorators using TSESTree types (e.g., TSInterfaceDeclaration, TSTypeAliasDeclaration, Decorator).
  • For TypeScript-specific syntax (generics, type annotations), use TSESTree node properties
  • Use #context7-mcp to find ESTree and TSESTree node types from typescript-eslint/typescript-eslint.

Testing Transformations

  • Use npm test to run tests.
  • Write tests using Vitest.
  • Use *.spec.ts filename convention.
  • Each transformation has a corresponding test file in the src folder.
  • Tests use createTestTransform to apply the transformation input and validate the output.
  • Use outdent tagged template literals to format multiline strings in the input and output.
  • Update expected transformation output in case of whitespace formatting issue in test