访问主模块

🌐 Accessing the main module

当一个文件直接从 Node.js 运行时，require.main 被设置为它的 module。这意味着可以通过测试 require.main === module 来判断一个文件是否被直接运行。

🌐 When a file is run directly from Node.js, require.main is set to its module. That means that it is possible to determine whether a file has been run directly by testing require.main === module.

对于文件 foo.js，如果通过 node foo.js 运行，则此值为 true；如果通过 require('./foo') 运行，则为 false。

🌐 For a file foo.js, this will be true if run via node foo.js, but false if run by require('./foo').

当入口点不是 CommonJS 模块时，require.main 为 undefined，主模块无法访问。

🌐 When the entry point is not a CommonJS module, require.main is undefined, and the main module is out of reach.