How to write Jest transformIgnorePatterns

Question

I have this excpetion

Jest encountered an unexpected token

    This usually means that you are trying to import a file which Jest cannot parse, e.g. it\'s not p         


        

Answer 1

I added this setting to my config, but no joy. Still getting the same error as Sergey Aslanvov.

"transformIgnorePatterns": [
  "/node_modules/(?!@vuetify)"
],

also tried

"transformIgnorePatterns": [
  "\\node_modules\\@vuetify",
],

Below is a sample of my component that extends VDataTable

import {
  Vue,
 Mixins,
 Component,
} from 'vue-property-decorator';

import { VDataTable } from 'vuetify/lib';

@Component
export class BPagedGrid extends Mixins(Vue, VDataTable) { }

Answer 2

I had a similar error while working on a project with jest, webpack, and vanilla js, so that error is thrown when jest encounters this line of code import '../css/styles.css'; in any /*?.js$/ file. I solved it by moving the jest configurations from the package.json file into a jest.config.js file with the following minimal configuration;

// jest.config.js
module.exports = 
  "moduleNameMapper": {
    "\\.(css|less|scss)$": "identity-obj-proxy"
  }
}

Then in babel.config.js

module.exports = {
  presets: [
    [
      '@babel/preset-env',
      {
        targets: {
          node: 'current',
        },
      },
    ],
  ],
};

Answer 3

Actually, it seems like typescript is not going well with JEST test cases, so what i feel like either JEST need to ignore those files or those packages need to be transpiled to js code which JEST can understand,

you can try this

"transformIgnorePatterns": [ "node_modules/(?!(@microsoft/sp-core-library))" ],

and in tsconfig.json

"allowJs": true,

for more details please check this post

https://github.com/SharePoint/sp-dev-docs/issues/2325#issuecomment-446416878

Answer 4

The transformIgnorePatterns means if the test path matches any of the patterns, it will not be transformed.

Note: DO NOT SPLIT MULTI-LINES.

The jest will ignore all node_modules via default.

So you must write like this:

"transformIgnorePatterns": [
  // all exceptions must be first line
  "/node_modules/(?!@microsoft/sp-core-library|sp-dialog|other_libs_need_transform)"
],