If you need a lightweight way of checking IBAN validity in a Typescript project, I've got you covered with an NPM. It's a conversion from a Swift library that I wrote years ago - partly prompted by needing the TS functionality, and partly by wanting to figure out the NPM publishing process.

The NPM is here -->

https://www.npmjs.com/package/iban-ts-validator

and the source is here -->

https://github.com/timd/iban-npm

Fully-tested with 100% coverage, go me...