pure-index

🌿 Pure Index

Pure Index is utility for monorepos. It helps to find unused exports from packages or get a list of all unique uses of any package.

Motivation

There is a package a which exports 2 functions

// "a" package index.ts file

export const T = () => true

export { myFn } from './myFn'

only 1 function from the package is used in the project

// some file

import { T } from 'a'

This means that package a exports myFn for nothing, so we can remove its export and possibly remove all the code. As the code base develops, a large number of such unnecessary exports may accumulate in the monorepo. Pure Index allows you to find such exports.

Usage

1. Install

npm install --save-dev pure-index

1. Add the check-exports script in the package.json of each package that needs to be checked

    "scripts": {
      "build": "webpack ./webpack.config.js",
+     "check-exports": "pure-index",
      "test": "vitest"
    }

1. Configure

2. Use flags if you need to override the config values for package

Config

Pure Index supports three ways to define config.

1. .pure-index.json config file:

{
  "entry": "index.ts",
  "exclude": ["node_modules"],
  "extensions": ["ts", "tsx"],
  "babelPlugins": ["typescript"],
  "batch": {
    "default": 100
  }
}

1. or pure-index section in package.json:

  "pure-index": {
    "entry": "index.ts",
    "exclude": ["node_modules"],
    "extensions": ["ts", "tsx"],
    "babelPlugins": ["typescript"],
    "batch": {
      "default": 100
    }
  }

1. or a more flexible .pure-index.js or .pure-index.cjs config file:

module.exports = {
  entry: 'index.ts',
  exclude: ['node_modules'],
  extensions: ['ts', 'tsx'],
  babelPlugins: ['typescript'],
  batch: {
    default: 100
  }
}

Arguments

• entry (String) — path to the package index file. relative to the package directory.
• exclude (Array<string>) — list of directories that will be excluded when searching for imports.
• extensions (Array<string>) — list of file extensions to be considered during the search.
• babelPlugins (Array<string>) — list of babel plugins that will be used when parsing files.
• batch.default (Number) — number of files to be traversed in parallel. changing the value may speed up or slow down the script. choose the value yourself.

CLI

Allows to override the config values for package.

--entry, -e

    "scripts": {
      "build": "webpack ./webpack.config.js",
-     "check-exports": "pure-index",
+     "check-exports": "pure-index --entry ./src/index.ts",
      "test": "vitest"
    }

--extensions, -x

    "scripts": {
      "build": "webpack ./webpack.config.js",
-     "check-exports": "pure-index",
+     "check-exports": "pure-index --extensions js,jsx,ts,tsx",
      "test": "vitest"
    }

--collect-usages, -u

Outputs a list of all unique uses of the package.

npx pure-index --collect-usages my-package
npx pure-index -u my-package

npx pure-index --collect-usages react-spring
npx pure-index -u react-spring

Useful if the package index file contains export * syntax. Or to search for all uses of an external package. More info

Tips

• Use knip or ts-prune to clean up unused code inside packages

Explanation

How It Works

In fact, the task is to compare all exports and imports of the package. Anything not imported but exported are unused exports.

Algorithm

1. collect all package exports into exports Set
2. traverse all files where package import may occur
3. if import is found, remove it from exports Set
4. if the size of exports exports Set became equal to 0, then exit with success
5. if exports Set size is not equal to 0, then exit with an error

How It Optimized

1. file reading is divided into batches
2. file is not immediately converted to AST. First the import of the package is searched for in the file. createReadStream is used
3. there is an instant exit with success as soon as the size of exports Set is equal to zero

Limitations

export *

Pure Index when getting a list of exports does not parse export * to find out what is exported from there. For projects with this syntax, it may result in an inability to use the library. But Pure Index can help with replacing export *. Just run it with the --collect-usages flag and replace export * with named exports.