build: add esm bundle

[nieyuyao]

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• It's submitted to the dev branch.
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• All tests are passing: https://github.com/vuejs/vue-test-utils/blob/dev/.github/CONTRIBUTING.md#development-setup
• New/updated tests are included

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information:

Provides an ESM bundle.

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[lmiller1990]

Cool, can you also add the exports field like so?

https://github.com/vuejs/test-utils/blob/main/package.json#L9-L15

[lmiller1990]

Thanks, will do a release soon :)

[wolfgangwalther]

Why was this added as-is, i.e. why with the import nesting? That breaks importing @vue/test-utils v1.3.1 in jest (non esm) for me with:

Cannot find module '@vue/test-utils' from '...'

    > 1 | import { createLocalVue } from '@vue/test-utils'

when I remove the import like this:

  "exports": {
    ".": {
      "node": "./dist/vue-test-utils.js",
      "require": "./dist/vue-test-utils.js",
      "default": "./dist/vue-test-utils.esm.js"
    }
  },

then it works again.

The comment that suggested to add the exports key was referencing this, i.e. the vue3 version of test-utils:

https://github.com/vuejs/test-utils/blob/main/package.json#L9-L15

There is no nested import there.

Maybe the following would be best?

  "exports": {
    ".": {
      "import": "./dist/vue-test-utils.esm.js",
      "require": "./dist/vue-test-utils.js",
      "default": "./dist/vue-test-utils.js"
    }
  },

That would be the most similar to what is done in vue/test-utils right now.

[lmiller1990]

Uh oh, did not realize this broke things. I'll patch this right now.

[lmiller1990]

#2020

[lmiller1990]

Done
https://github.com/vuejs/vue-test-utils/releases/tag/v1.3.2

Gave it a quick test, seems okay, LMK if you run into any problems.

[wolfgangwalther]

Thanks that fixed it!