Docs: Troubleshoot import statement

[greenbourne277]

Summary

When setting up a project with @vue/cli (https://github.com/vuejs/vue-cli) with version 4.5.13 with ts-jest I faced the problem that the test could not be executed for my component because one of the modules doesn't need to be transpiled.
I found this answer after searching for a long time on the web and therefore thought it should be added to the documentation of the project.

Test plan

There are no changes in the code. In can be tested as follows:

1. Setup a vue project with vue-cli: vue create project
2. Select Vue2.x, typescript, jest and babel
3. Add the vue-class-component package via npm install --save vue vue-class-component
4. Adapt the HelloWorld.vue component:

<script lang="ts">
import Vue from "vue";
import Component from "../../node_modules/vue-class-component/lib";

@Component
export default class HelloWorld extends Vue {
  name = "HelloWorld"
};
</script>

5. Run the test via npm run test:unit and verify the error message.
6. To fix this issue adapt the jest.config.js as following:

module.exports = {
  preset: "@vue/cli-plugin-unit-jest/presets/typescript-and-babel",
  transformIgnorePatterns: ["node_modules/(?!(vue-class-component))"]
};

Does this PR introduce a breaking change?

• Yes
• No

Other information

[ahnpnl]

pls put a blank line between ### SOLUTION and the description below

[ahnpnl]

I would strip out the stuffs related to Vue, in this case this line 54, 55

[ahnpnl]

Actually transformIgnorePatterns means:

I don't want to transform x,y,z modules. 

However, the error SyntaxError: Cannot use import statement outside a module has a different meaning.

It means

This module is not in the syntax which Jest can execute. You need to ask Jest to transform it.

The regex in your example has a ! which tells Jest to NOT ignore those modules in transformation step, which means Jest needs to transform those modules.

[greenbourne277]

Thanks for pointing this out and your explanation. I will change it.

[coveralls]

Pull Request Test Coverage Report for Build 1115888734

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 94.366%

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Totals
Change from base Build 1106605705:	0.0%
Covered Lines:	1084
Relevant Lines:	1110

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💛 - Coveralls

[ahnpnl]

You would need to run lint-prettier :)

[ahnpnl]

Thanks!