Stopped working on Node.js v10.24: "Error: Not supported" caused by ESM import

[alexander-fenster]

Prerequisites

• Checked that your issue hasn't already been filed by cross-referencing issues with the faq label
• Checked next-gen ES issues and syntax problems by using the same environment and/or transpiler configuration without Mocha to ensure it isn't just a feature that actually isn't supported in the environment in question or a bug in your code.
• 'Smoke tested' the code to be tested by running it outside the real test suite to get a better sense of whether the problem is in the code under test, your usage of Mocha, or Mocha itself
• Ensured that there is no discrepancy between the locally and globally installed versions of Mocha. You can find them with: node node_modules/.bin/mocha --version(Local) and mocha --version(Global). We recommend that you not install Mocha globally.

Description

In lib/esm-utils.js, hasStableEsmImplementation returns true on Node.js v10.24.1 even though it must only return true on versions >= 12.22.

Steps to Reproduce

In the cloned mocha repository:

$ node -e 'const path = require("path"); const utils = require("./lib/esm-utils"); utils.requireOrImport(path.resolve("./index.js"))'

Expected behavior: [What you expect to happen]

No error

Actual behavior: [What actually happens]

(node:22250) UnhandledPromiseRejectionWarning: Error: Not supported
    at formattedImport (/Users/fenster/repos/mocha/lib/esm-utils.js:7:31)
    at Object.exports.requireOrImport.hasStableEsmImplementation [as requireOrImport] (/Users/fenster/repos/mocha/lib/esm-utils.js:46:38)
    at [eval]:1:79
    at Script.runInThisContext (vm.js:122:20)
    at Object.runInThisContext (vm.js:329:38)
    at Object.<anonymous> ([eval]-wrapper:6:22)
    at Module._compile (internal/modules/cjs/loader.js:778:30)
    at evalScript (internal/bootstrap/node.js:590:27)
    at startup (internal/bootstrap/node.js:265:9)
    at bootstrapNodeJSCore (internal/bootstrap/node.js:623:3)

Reproduces how often: [What percentage of the time does it reproduce?]

100%

Versions

9.0.0

• The output of mocha --version and node node_modules/.bin/mocha --version:
• The output of node --version:
• Your operating system
  • name and version:
  • architecture (32 or 64-bit):
• Your shell (e.g., bash, zsh, PowerShell, cmd):
• Your browser and version (if running browser tests):
• Any third-party Mocha-related modules (and their versions):
• Any code transpiler (e.g., TypeScript, CoffeeScript, Babel) being used (and its version):

Additional Information

[juergba]

In lib/esm-utils.js, hasStableEsmImplementation returns true on Node.js v10.24.1 even though it must only return true on versions >= 12.22.

We dropped support of Node v10 in Mocha v9.0.0 as a breaking change.

[alexander-fenster]

@juergba I understand that :) My point here is that if it was hard to backport the code to keep it working on Node 10, it would've been a fair deal to drop it completely and not accept any fixes. In this particular case though, it's just a matter of a small (and correct) fix which might keep the code working on the older versions for the time being.

Of course we'll be able to pin our workflows to 8.x (since we do need to keep supporting Node 10 for a little bit longer), but - again - I personally don't like the idea of breaking the stuff that can still work. Up to you though :)

[juergba]

@alexander-fenster I like clear cuts, but could live with your change.

@giltayar cc

[williamdes]

I had this error on Node 12 :/
See: https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c#gistcomment-3762987

[williamdes]

I am on Node v12.16.2

You can see my migration to use back the module after upgrading to Mocha v9: sudo-bot/gh-deployer@3965e27

Error: Not supported
    at formattedImport (/mnt/Dev/@sudo/gh-deployer/node_modules/mocha/lib/esm-utils.js:7:31)
    at Object.implementationOfRequireOrImportForUnstableEsm [as requireOrImport] (/mnt/Dev/@sudo/gh-deployer/node_modules/mocha/lib/esm-utils.js:87:14)
    at Object.exports.loadFilesAsync (/mnt/Dev/@sudo/gh-deployer/node_modules/mocha/lib/esm-utils.js:71:34)
    at Mocha.loadFilesAsync (/mnt/Dev/@sudo/gh-deployer/node_modules/mocha/lib/mocha.js:467:19)
    at singleRun (/mnt/Dev/@sudo/gh-deployer/node_modules/mocha/lib/cli/run-helpers.js:125:15)
    at exports.runMocha (/mnt/Dev/@sudo/gh-deployer/node_modules/mocha/lib/cli/run-helpers.js:190:10)
    at Object.exports.handler (/mnt/Dev/@sudo/gh-deployer/node_modules/mocha/lib/cli/run.js:366:11)
    at /mnt/Dev/@sudo/gh-deployer/node_modules/yargs/build/index.cjs:443:71

[juergba]

@williamdes this issue is about Mocha v9 and javascript.

As far as I can see you have had your issue 12 days ago, at that time Mocha v9 hasn't been published yet.
Furthermore you are on typescript and ts-node, sindresorhus is explaining in his guide what has to be done in this case.

Edit: I recommend to pin your sindresorhus dependency to a version before pure ESM. Otherwise you will have to invest some time to get through this experimental esm-loader-story. It's not really fun.