process.mainModule to require.main

Replace process.mainModule with require.main in CommonJS modules (DEP0138)

This recipe transforms usage of the deprecated process.mainModule to use require.main in CommonJS modules.

Deprecation

Node.js deprecated process.mainModule in favor of require.main for CommonJS modules.

See DEP0138 for more details.

Usage

Run this codemod with:

npx codemod nodejs/process-main-module

Before/After

- if (process.mainModule === "mod.js") {
+ if (require.main === "mod.js") {
    // cli thing
  } else {
    // module thing
  }

What It Does

• Replaces all instances of process.mainModule with require.main
• Works with any comparison or assignment pattern
• Preserves the rest of your code logic

Common Use Cases

Detecting if Module is Main

- if (process.mainModule === module) {
+ if (require.main === module) {
    // This file was executed directly
    main();
  } else {
    // This file was imported
    module.exports = { main };
  }

Accessing Main Module Properties

- const mainFilename = process.mainModule.filename;
+ const mainFilename = require.main.filename;

- const mainDir = process.mainModule.path;
+ const mainDir = require.main.path;

This replacement only applies to CommonJS modules. For ESM modules, use import.meta.url to determine the entry point.

The pattern require.main === module is a common way to check if a script was run directly or imported as a module, enabling dual-mode usage.