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Test if an ES module is run directly (require.main replacement)

Home Page: https://www.npmjs.com/package/es-main

JavaScript 100.00%

es-main's Introduction

es-main

Test if an ES module is run directly with Node.js. Acts as a replacement for require.main.

use

import esMain from 'es-main';

if (esMain(import.meta)) {
  // Module run directly.
}

why?

It can be useful to have a module that is both imported from other modules and run directly. With CommonJS, it is possible to have a top-level condition that checks if a script run directly like this:

if (require.main === module) {
  // Do something special.
}

With ES modules in Node.js, require.main is not available. Other alternatives like process.mainModule and module.parent are also not defined for ES modules. In the future, there may be an alternative way to do this check (e.g. import.meta.main or a special main export). Until then, this package provides a workaround.

es-main's People

Contributors

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xamgore jridgewell loynoir xbsl zorgatone web4more

es-main's Issues

esMain(import.meta) pops an error

Hey,

I am getting the following error with esMain(import.meta) line:

iMac:api ninjablade$ sls deploy
Serverless: Bundling with Webpack...

ERROR in /Volumes/Work/Work/Workspace/+Purpose/Backend/services/api/user.js 105:17
Module parse failed: Unexpected token (105:17)
File was processed with these loaders:
 * ../../babel-loader/lib/index.js
 * ../node_modules/eslint-loader/dist/cjs.js
You may need an additional loader to handle the result of these loaders.
| });
| 
> if (esMain(import.meta)) {
|   get(mock);
| }

ERROR in /Volumes/Work/Work/Workspace/+Purpose/Backend/services/api/user.js 105:17
Module parse failed: Unexpected token (105:17)
File was processed with these loaders:
 * ../../babel-loader/lib/index.js
 * ../node_modules/eslint-loader/dist/cjs.js
You may need an additional loader to handle the result of these loaders.
| });
| 
> if (esMain(import.meta)) {
|   get(mock);
| }
 
 Error ---------------------------------------------------
 
  Error: Webpack compilation error, see stats above
      at /Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/serverless-webpack/lib/compile.js:32:15
      at arrayEach (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/lodash/lodash.js:530:11)
      at Function.forEach (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/lodash/lodash.js:9410:14)
      at /Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/serverless-webpack/lib/compile.js:29:7
      at tryCatcher (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/bluebird/js/release/util.js:16:23)
      at Promise._settlePromiseFromHandler (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/bluebird/js/release/promise.js:547:31)
      at Promise._settlePromise (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/bluebird/js/release/promise.js:604:18)
      at Promise._settlePromise0 (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/bluebird/js/release/promise.js:649:10)
      at Promise._settlePromises (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/bluebird/js/release/promise.js:729:18)
      at Promise._fulfill (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/bluebird/js/release/promise.js:673:18)
      at /Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/bluebird/js/release/nodeback.js:42:21
      at finalCallback (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/webpack/lib/Compiler.js:257:39)
      at /Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/webpack/lib/Compiler.js:273:13
      at AsyncSeriesHook.eval [as callAsync] (eval at create (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:6:1)
      at AsyncSeriesHook.lazyCompileHook (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/tapable/lib/Hook.js:154:20)
      at onCompiled (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/webpack/lib/Compiler.js:271:21)
      at /Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/webpack/lib/Compiler.js:681:15
      at AsyncSeriesHook.eval [as callAsync] (eval at create (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:6:1)
      at AsyncSeriesHook.lazyCompileHook (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/tapable/lib/Hook.js:154:20)
      at /Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/webpack/lib/Compiler.js:678:31
      at AsyncSeriesHook.eval [as callAsync] (eval at create (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:6:1)
      at AsyncSeriesHook.lazyCompileHook (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/tapable/lib/Hook.js:154:20)
      at /Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/webpack/lib/Compilation.js:1423:35
      at AsyncSeriesHook.eval [as callAsync] (eval at create (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:6:1)
      at AsyncSeriesHook.lazyCompileHook (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/tapable/lib/Hook.js:154:20)
      at /Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/webpack/lib/Compilation.js:1414:32
      at AsyncSeriesHook.eval [as callAsync] (eval at create (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:6:1)
      at AsyncSeriesHook.lazyCompileHook (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/tapable/lib/Hook.js:154:20)
      at /Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/webpack/lib/Compilation.js:1409:36
      at AsyncSeriesHook.eval [as callAsync] (eval at create (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:6:1)
      at AsyncSeriesHook.lazyCompileHook (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/tapable/lib/Hook.js:154:20)
      at /Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/webpack/lib/Compilation.js:1405:32
      at AsyncSeriesHook.eval [as callAsync] (eval at create (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:6:1)
      at AsyncSeriesHook.lazyCompileHook (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/tapable/lib/Hook.js:154:20)
      at Compilation.seal (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/webpack/lib/Compilation.js:1342:27)
      at /Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/webpack/lib/Compiler.js:675:18
      at /Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/webpack/lib/Compilation.js:1261:4
      at AsyncSeriesHook.eval [as callAsync] (eval at create (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:24:1)
      at AsyncSeriesHook.lazyCompileHook (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/tapable/lib/Hook.js:154:20)
      at Compilation.finish (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/webpack/lib/Compilation.js:1253:28)
      at /Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/webpack/lib/Compiler.js:672:17
      at eval (eval at create (/Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:11:1)
      at /Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/webpack/lib/Compilation.js:1185:12
      at /Volumes/Work/Work/Workspace/+Purpose/Backend/node_modules/webpack/lib/Compilation.js:1097:9
      at processTicksAndRejections (internal/process/task_queues.js:75:11)
 
     For debugging logs, run again after setting the "SLS_DEBUG=*" environment variable.
 
  Get Support --------------------------------------------
     Docs:          docs.serverless.com
     Bugs:          github.com/serverless/serverless/issues
     Issues:        forum.serverless.com
 
  Your Environment Information ---------------------------
     Operating System:          darwin
     Node Version:              14.16.1
     Framework Version:         2.52.1
     Plugin Version:            5.4.3
     SDK Version:               4.2.3
     Components Version:        3.14.2

The strange thing is that this is only happening with webpack bundling.. when I run it locally, it doesn't have any error.

Add TypeScript types

Consider adding a main.d.ts with:

export default function (meta: ImportMeta): boolean;

Workaround:

declare module 'es-main' {
  export default function (meta: ImportMeta): boolean;
}

Does not support index.js resolve

node foo can run foo/index.js, but esMain() returns false with that.

Does not support main module resolve

This lib does not work for the package.json below:

{
  "name": "foo",
  "version": "1.2.3",
  "description": "Package with custom main field",
  "main": "foo.js",
  "type": "module",
  "scripts": {
    "start": "node ."
  }
}

When running npm start on the project above, the argv[1] returns the directory where the project lives, but without the main module at the end.

Since this is supported by the package.json spec, I would like to add support for it here too.

usage should be updated

Example in readme

A library available for browser, also provide cli.
When using bundler,

import esMain from 'es-main';

// library code

if (esMain(import.meta)) {
  // cli only code
}

Expected

// library code

Actual

// es-main source code

// library code

if (esMain(import.meta)) {
  // cli only code
}

Pull

#15

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