Correct esm problem on windows #559

David-Desmaisons · 2021-08-17T03:05:08Z

When using tape on windows in a esm module (using "type": "module" in the project package.json), this exception is raised:

(node:7484) UnhandledPromiseRejectionWarning: Error [ERR_UNSUPPORTED_ESM_URL_SCHEME]: Only file and data URLs are
supported by the default ESM loader
    at Loader.defaultResolve [as _resolve] (internal/modules/esm/resolve.js:698:11)
    at Loader.resolve (internal/modules/esm/loader.js:97:40)
    at Loader.getModuleJob (internal/modules/esm/loader.js:243:28)
    at Loader.import (internal/modules/esm/loader.js:178:28)
    at importModuleDynamically (internal/modules/cjs/loader.js:1080:27)
    at exports.importModuleDynamicallyCallback (internal/process/esm_loader.js:37:14)
    at importOrRequire (C:\...\tests\node_modules\tape\bin\import-or-require.js:11:9)       
    at C:\...\tests\node_modules\tape\bin\tape:84:14
    at Array.reduce (<anonymous>)
    at importFiles (C:\...\tests\node_modules\tape\bin\tape:81:30)

In turns out that making explicit the file protocol in the importOrRequire resolves this problem.

ljharb · 2021-08-17T04:54:51Z

bin/import-or-require.js

@@ -8,7 +8,7 @@ module.exports = function importOrRequire(file) {
    const ext = extnamePath(file);

    if (ext === '.mjs' || (ext === '.js' && getPackageType.sync(file) === 'module')) {
-        return import(file);
+        return import("file://" + file);


this will break if someone uses --require=packageName. You need to provide the flle:// on relative ESM paths yourself, I think.

I am still not sure about the --import=packageName (only find the require and ignore option). Could you please give an example that would break with this fix?

David-Desmaisons · 2021-08-17T14:01:50Z

I just made a test with the --require option and it seems that it is not calling the importOrRequire function:

Is it correct or I am missing something?

ljharb · 2021-08-17T14:47:28Z

Sorry, you’re right; i meant --import=packageName

ljharb · 2021-08-17T14:48:03Z

Also, on what node version are you seeing this issue? And what exact tape command are you running?

David-Desmaisons · 2021-08-17T15:26:12Z

Here is a minimal repo for reproduction using tape **/*.spec.js command:
https://github.com/David-Desmaisons/tape-tests

I am testing with node 12.

ljharb · 2021-08-17T15:27:36Z

You can’t pass unquoted globs to tools tho - your shell will expand them. Try putting quotes around the glob.

If that doesn’t fix it, I’ll take a look at your repro repo shortly.

David-Desmaisons · 2021-08-17T15:44:16Z

I changed to:

  "scripts": {
    "test": "tape \"**/*.spec.js\""
  },

With the same results: it works on ubuntu but breaks on windows.

ljharb · 2021-08-17T18:21:38Z

interesting, ok. it's also notable you're not using --import or --require, which means this line of code shouldn't be executed. I don't have Windows to be able to test, unfortunately.

ljharb · 2021-08-18T05:26:00Z

Indeed, your repo passes fine on my Mac.

David-Desmaisons · 2021-08-20T02:49:36Z

The path are constructed line 59 of tape.js file

It is then used using the import sintax but as on windows it is a windows path it is not compatible with an url:

Adding "file:\\" before the path resolve the windows case without breaking linux build.

vweevers · 2021-11-13T15:33:39Z

bin/import-or-require.js

@@ -8,7 +8,7 @@ module.exports = function importOrRequire(file) {
    const ext = extnamePath(file);

    if (ext === '.mjs' || (ext === '.js' && getPackageType.sync(file) === 'module')) {
-        return import(file);
+        return import('file://' + file);


I'm seeing the same issue on Windows (with node 16.9.1).

I suggest import(pathToFileURL(file).href), using const { pathToFileURL } = require('url') which was added in node 10.12.0. Prior art: unified-engine.

PS. The error message that I'm getting has a more complete explanation than the message shared in the OP. Running tape test.js yields:

Error [ERR_UNSUPPORTED_ESM_URL_SCHEME]: Only file and data URLs are supported by the default ESM loader. On Windows, absolute paths must be valid file:// URLs. Received protocol 'c:'

That test.js file is an ESM file on C:\, within a package with { "type": "module" }, therefore hitting the import() if-branch as expected.

@ljharb See nodejs/node@a084632. The error message was further tweaked in a later commit, but this should suffice to explain it.

@vweevers that makes sense, but I still need to find a way to repro it on windows (but i don't have a windows box) or a test that would have failed on windows (even though we're not running tests on windows yet)

Would you take a PR for a basic windows workflow on GitHub Actions (just on latest node to start), with a test? Can split those into 2 PRs if you prefer that

Yes, but I prefer not to use the setup-node action, and I haven't yet adapted https://github.com/ljharb/actions/tree/main/node/install to work on windows yet.

OK, in that case I'll only send a PR for a test (if I can get existing tests to pass on Windows).

This is required on Windows if the argument passed to `import()` is an absolute path. Without it `tape test.js` fails if test.js is ESM. Covered by existing tests: `node test/import.js` fails without this. See nodejs/node@a084632

ljharb · 2021-11-14T00:10:34Z

@David-Desmaisons thank you so much for bringing the problem to my attention; I'm going to go with the solution in #571, and longer term, we'll look into running CI tests on windows to prevent this kind of problem in the future.

- [Fix] use `file://` URLs for dynamic `import()` (#571, #559) - [readme] hard wraps bad, soft wraps good - [readme] fix markdown; github still has a rendering bug - [readme] add badges - [meta] Exclude `fs` from browser bundles (#565) - [Deps] update `glob`, `string.prototype.trim` - [Dev Deps] update `eslint`, `@ljharb/eslint-config`, `safe-publish-latest`, `array.prototype.flatmap` - [actions] update codecov uploader - [Tests] handle carriage returns in stack traces on Windows - [Tests] node 17+ smooshes a version number on the end of the stack trace - [Tests] handle v8 6.9 changing an error message

ljharb requested changes Aug 17, 2021

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vweevers reviewed Nov 13, 2021

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[Fix] use file:// URLs for dynamic import()

d487add

This is required on Windows if the argument passed to `import()` is an absolute path. Without it `tape test.js` fails if test.js is ESM. Covered by existing tests: `node test/import.js` fails without this. See nodejs/node@a084632

vweevers mentioned this pull request Nov 13, 2021

[Fix] use file:// URLs for dynamic import() #571

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ljharb force-pushed the correct-esm-problem-windows branch from 9179395 to d487add Compare November 14, 2021 00:09

ljharb approved these changes Nov 14, 2021

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ljharb merged commit d487add into tape-testing:master Nov 14, 2021

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Correct esm problem on windows #559

Correct esm problem on windows #559

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Correct esm problem on windows #559

Correct esm problem on windows #559

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