`if __name__ == '__main__'` equivalent in javascript es6 modules

Question

Is it possible to check if JavaScript file is being run directly or if it was required as part of an es6 module import.

for example a main script is included.

// main.js
import './other';

if (mainTest){
  console.log('This should run');
}

which imports a dependency.

// other.js
if (mainTest){
  console.log('This should never run');
}

including <script src=main.js></script> should result in the console message from main.js but not other.js.

I found the answer to this question with regards to node, but I am interested specifically for es6 imports

Answer 1

An alternative for ES6 modules is now supported in Node. Using the new import.meta builtin.

Example:

// main.mjs
import "./lib.mjs"
import { fileURLToPath } from "url";

if (process.argv[1] === fileURLToPath(import.meta.url)) {
  console.log(`main ran!`);
}

// lib.mjs
import { fileURLToPath } from "url";

if (process.argv[1] === fileURLToPath(import.meta.url)) {
  console.log(`lib ran!`);
}

and our output:

main ran!