provideHighcharts() fails with vitest 4.1.0+

[georgmu]

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Describe the bug

When using vitest 4.1.0 with a spec.ts which uses provideHighcharts(), the import of highcharts fails:

Error: Cannot find module '.../node_modules/highcharts/esm/highcharts' imported from .../node_modules/highcharts-angular/fesm2022/highcharts-angular.mjs
Did you mean to import "highcharts/esm/highcharts.js"?
 ❯ finalizeResolution node:internal/modules/esm/resolve:275:11
 ❯ moduleResolve node:internal/modules/esm/resolve:865:10
 ❯ defaultResolve node:internal/modules/esm/resolve:991:11
 ❯ ModuleLoader.#cachedDefaultResolve node:internal/modules/esm/loader:719:20
 ❯ ModuleLoader.#resolveAndMaybeBlockOnLoaderThread node:internal/modules/esm/loader:736:38
 ❯ ModuleLoader.resolveSync node:internal/modules/esm/loader:765:52
 ❯ ModuleLoader.#resolve node:internal/modules/esm/loader:701:17
 ❯ ModuleLoader.getOrCreateModuleJob node:internal/modules/esm/loader:621:35
 ❯ onImport.tracePromise.__proto__ node:internal/modules/esm/loader:650:32
 ❯ TracingChannel.tracePromise node:diagnostics_channel:350:14

This was working with vitest up to version 4.0, but now fails. from the backlog, it relies on node.js, which requires the extension ( https://nodejs.org/api/esm.html#mandatory-file-extensions )

Fix

So the fix is to simply add the .js suffix to the import statement in highcharts-angular.mjs.

Work-arounds

The work-around is to provide a vitest.config.ts (and register it via angular.json) to inline highcharts-angular:

import { defineConfig } from 'vitest/config';

export default defineConfig({
  test: {
    server: {
      deps: {
        inline: ['highcharts-angular']
      }
    }
  }
});

The other work-around is to provide the instance in the spec file (here it works with or without the '.js' suffix):

provideHightcharts({
  instance: () => import('highcharts/esm/highcharts').then(m => m.default)
})

Expected behavior

Given angular is focusing on vitest, it should run without any work-arounds.

Demo

1. Create an angular app with vitest test runner
2. add provideHighcharts() the the providers in the testbed configuration

Setup used

Angular CLI : 21.2.7
Angular : 21.2.8
Node.js : 24.14.1
Package Manager : npm 11.11.0
Operating System : linux x64