Jest is tricky to get working with ESM code. jestjs/jest#13739

Specifically when tests are written in TypeScript. https://kulshekhar.github.io/ts-jest/docs/guides/esm-support/

...and their recommended configuration requires a newer version of ts-jest than 29.1.0, which is from 2023. 29.2.0 added a bunch of ESM config helpers.

...and because Jest writes its own require() logic as part of its mocking feature, it's more restrictive than Node.js v20.19 which allows CJS code (the Jest test) to require() ESM code (the xchainjs module). Jest won't allow that, so the test has to be ESM too.

...except the tests aren't ESM. There are a whole ton of require() calls that are used to read and parse a nearby JSON file. They can't work in ESM:

 ReferenceError: require is not defined

In order to make Jest work, since currently the tests only work when transpiled to CJS, and Jest refuses to let CJS code require ESM code, had to resort to conditional exports:

 "exports": {
 "require": "./lib/index.cjs",
 "import": "./lib/index.esm.js"
 },

Never mind. The built ESM code in xchain-cosmos/kujira/thorchain/mayachain (and probably anything that depends on them) just doesn't work.

It only maybe works if a transpiler messes with it. Raw, it fails trying to import from cosmos/cosmjs-types#93

Error [ERR_MODULE_NOT_FOUND]: Cannot find module 'xchainjs-lib/node_modules/cosmjs-types/cosmos/tx/v1beta1/tx' imported from xchainjs-lib/packages/xchain-cosmos/lib/index.esm.js
Did you mean to import cosmjs-types/cosmos/tx/v1beta1/tx.js?

CosmJs packages are only very lightly maintained by Confio these days, and they're all effectively CommonJs-only right now. cosmos/cosmjs#1649 (comment)

Since it's not exported from the top level index.ts at all, the only ESM-compatible way to access that type is importing as .../tx.js.