Detect if the current file/module is the entrypoint or import/require-d in Node.js

How does one identify whether a JavaScript file is being run directly (node file.js) or it’s being import/require-d (require('./file') in another JS file).

In Python the pattern leverages the __main__ property in modules like so:

if __name__ == '__main__':
  # do something
  # or not
  pass

The equivalent code in Node.js/JavaScript would be:

if (require.main === module) {
  // do something
  // or nothing
}

Detecting whether a module/file is the Node.js entrypoint or required/imported

Say we have a file/module entry-or-not.js:

function isEntryPoint() {
  return require.main === module;
}

console.log(isEntryPoint());

If we run the file directly it should return true:

$ node entry-or-not.js
true

If require through the REPL whether we eval or actually go into the REPL, it should be false:

$ node -e "require('./entry-or-not')"
false

and

$ node
> require('./entry-or-not')
false
{}

If we require/import from another module another-module.js:

require('./entry-or-not');

And run that module as the Node.js entry point.

$ node another-module.js
false

Further Reading

Accessing the main module - Node.js Documentation.

Photo by Benjamin Lambert