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doc: confusing support for extensionless ESM #30655

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azz opened this issue Nov 26, 2019 · 5 comments
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doc: confusing support for extensionless ESM #30655

azz opened this issue Nov 26, 2019 · 5 comments
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esm Issues and PRs related to the ECMAScript Modules implementation. experimental Issues and PRs related to experimental features.

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@azz
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azz commented Nov 26, 2019

From the ESM docs (emphasis mine):

import statements of .js and extensionless files are treated as ES modules if the nearest parent package.json contains "type": "module".

Unless I am mistaken (discussed in nodejs/modules#443), extensionless module resolution is not currently supported.

How can you have an import statement for an extensionless file when it does not resolve?

@azz
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azz commented Nov 26, 2019

Ah I forgot about --es-module-specifier-resolution=node. Perhaps worth leaving a link to this flag in that area of the docs?

@yorkie
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yorkie commented Nov 26, 2019

It seems that is documented at that page, see: https://nodejs.org/api/esm.html#esm_code_package_json_code_code_type_code_field.

@azz
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azz commented Nov 26, 2019

It's documented at the very bottom of the page. Maybe update the example to say something like this? I feel like a lot of people are (like me!) going to run into this when switching to the native ESM loader.

 // my-app.js, part of the same example as above
 import './startup.js'; // Loaded as ES module because of package.json
+
+// Requires --es-module-specifier-resolution=node
+import './startup'; // Loaded as ES module because of package.json

azz added a commit to azz/node that referenced this issue Nov 26, 2019
@MylesBorins
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Commented in the PR

TL;DR
Extensionless files, as documented, are different from extensionless specifiers.

extensionless filepath and specifier

  • path /path/to/file
  • specifier import './file'

filepath with extension and extensionless specifier

  • path /path/to/file.js
  • specifier import './file'

@devsnek devsnek added esm Issues and PRs related to the ECMAScript Modules implementation. experimental Issues and PRs related to experimental features. labels Dec 3, 2019
@Alhadis
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Alhadis commented Dec 7, 2019

I have an extensionless file (which is an executable) failing to be imported, despite package.json containing "type": "module":

λ JG (master): cat ./test.mjs
#!/usr/bin/env node

import "./bin/list";
λ JG (master): head bin/list
#!/usr/bin/env node
import {join, resolve} from "path";


λ JG (master): ./test.mjs
(node:4311) ExperimentalWarning: The ESM module loader is experimental.
internal/modules/run_main.js:50
    internalBinding('errors').triggerUncaughtException(
                              ^

TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension: /Users/john/Labs/JG/bin/list
    at Loader.resolve [as _resolve] (internal/modules/esm/default_resolve.js:114:13)
    at Loader.resolve (internal/modules/esm/loader.js:74:33)
    at Loader.getModuleJob (internal/modules/esm/loader.js:148:40)
    at ModuleWrap.<anonymous> (internal/modules/esm/module_job.js:41:40)
    at link (internal/modules/esm/module_job.js:40:36) {
  code: 'ERR_UNKNOWN_FILE_EXTENSION'
}

This happens both with static and dynamic imports.

Current Node version: v13.2.0

BridgeAR pushed a commit that referenced this issue Jan 3, 2020
Fixes: #30655

PR-URL: #30657
Reviewed-By: Yorkie Liu <yorkiefixer@gmail.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
MylesBorins pushed a commit that referenced this issue Jan 12, 2020
Fixes: #30655

PR-URL: #30657
Reviewed-By: Yorkie Liu <yorkiefixer@gmail.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
BethGriggs pushed a commit that referenced this issue Feb 6, 2020
Fixes: #30655

PR-URL: #30657
Reviewed-By: Yorkie Liu <yorkiefixer@gmail.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
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