add-function-return-types

A CLI tool and library that adds explicit return types to TypeScript functions using type inference.

About

TypeScript can infer return types, but explicit return types improve readability, catch accidental changes, and are required by linting rules like @typescript-eslint/explicit-function-return-type. This tool adds them automatically by analyzing your code with ts-morph.

Installation

npm install -g add-function-return-types

Or run directly with npx:

npx add-function-return-types

Requirements

• Node.js >= 20

Usage

add-function-return-types [path] [options]

By default, the tool:

• Uses the current working directory as the root path
• Processes all .ts and .tsx files recursively
• Ignores node_modules and .d.ts files
• Saves files in place with the added return types

Examples

Process the current directory:

add-function-return-types

Process a specific directory:

add-function-return-types src/

Ignore generated files and specific functions:

add-function-return-types --ignore-files "src/generated/**,tests/**" --ignore-functions "map,filter"

Preview changes without modifying files:

add-function-return-types --dry-run

Use a specific tsconfig for type resolution:

add-function-return-types --tsconfig tsconfig.app.json

Programmatic API

The core function can also be imported directly:

import { addFunctionReturnTypes } from 'add-function-return-types'

await addFunctionReturnTypes({
	path: './src',
	shallow: false,
	overwrite: false,
	ignoreFiles: ['src/generated/**'],
	ignoreFunctions: [],
	ignoreAny: false,
	ignoreUnknown: false,
	ignoreAnonymousObjects: false,
	ignoreAnonymousFunctions: false,
	ignoreExpressions: false,
	ignoreFunctionsWithoutTypeParameters: false,
	ignoreHigherOrderFunctions: false,
	ignoreTypedFunctionExpressions: false,
	ignoreIIFEs: false,
	ignoreConciseArrowFunctionExpressionsStartingWithVoid: false,
	dryRun: false,
	tsconfig: undefined
})

Options

| Option | Description | | ---------------------------------------------------------------- | --------------------------------------------------------------- | | --shallow | Only process the top-level directory (no recursion) | | --overwrite | Overwrite functions that already have return types | | --ignore-files <patterns> | Comma-separated file glob patterns to ignore | | --ignore-functions <names> | Comma-separated function/method names to ignore | | --ignore-any | Skip functions that return any | | --ignore-unknown | Skip functions that return unknown | | --ignore-anonymous-objects | Skip functions that return anonymous object types | | --ignore-anonymous-functions | Skip anonymous functions (functions without names) | | --ignore-expressions | Skip function expressions (not part of a declaration) | | --ignore-functions-without-type-parameters | Skip functions without generic type parameters | | --ignore-higher-order-functions | Skip functions that immediately return another function | | --ignore-typed-function-expressions | Skip function expressions with type annotations on the variable | | --ignore-iifes | Skip immediately-invoked function expressions | | --ignore-concise-arrow-function-expressions-starting-with-void | Skip arrow functions starting with void | | --dry-run | Preview changes without modifying files | | --tsconfig <path> | Path to a tsconfig.json file for type resolution |

Contributing

Contributions are welcome! Feel free to open an issue or submit a pull request.

Development setup

git clone https://github.com/brandhaug/add-function-return-types.git
cd add-function-return-types
npm install
npm run build

Running tests

npm test

License

This project is licensed under the MIT License.