Why doesn't Jest understand the syntax?. in the imported file?

Question

JavaScript

1. Created an npm package with a useful feature. Tested with jest, published on npm
2. Checked on codesandbox, importing the package and running the function - everything works fine
3. Now I create another package, into which I import the first one and when I run the tests through jest I get an error

Jest encountered an unexpected token

This usually means that you are trying to import a file which Jest cannot parse, eg it's not plain JavaScript.

By default, if Jest sees a Babel config, it will use that to transform your files, ignoring "node_modules".

Details:

C:\OSPanel\domains\localhost\js projects\sql-for-js-simple\node_modules\split-smartly\index.js:452 (searchSettings.mentions?.[fragment] && ACTION_ADD_FRAGMENT) ^

SyntaxError: Unexpected token .

That is, it swears at the syntax searchSettings.mentions?.[fragment]

in the imported file, despite the fact that this syntax works fine in the project itself.
Question: what am I doing wrong?

Link to the project where the error occurs (only when importing into another project and running tests via jest)
https://github.com/dimoff66/split-smartly

Answer 1

Apparently your other project is not configured to understand the syntax "?."
The message from jest is quite informative

"This usually means that you are trying to import a file which Jest cannot parse, eg it's not plain JavaScript.
By default, if Jest sees a Babel config, it will use that to transform your files, ignoring "node_modules.""

you either need to put the babel config the same to understand the new syntax, or compile your code with the same babel into an older standard