Ok so I finally created an account just to respond to this post because I wanted to share my experience with typescript.
I really don't get the confusion and doubts about the usefulness of typescript. It's my favorite language to use because of it's expressiveness.
In my company we built a lot of web apps in very small teams (mostly just 2 people). We use mostly c# as a backend and typescript + mostly angular, sometimes react as a frontend. When typescript came out I built a conversion utility that allows me to generate typescript definitions and metadata from my c# type definitions. In angular I built my own type safe reactive forms, access control and API framework. Often we use ef core as a database layer on the backend, so we have a single source of truth (the c# types) for database and frontend types for the API. I use mapped types in typescript a lot to reuse the generated API types in my frontend code. If a field in a class is renamed ef core takes care of the database migration. On the frontend I get notified of every error because of the rename. Is there a table column for the field, I get an error. Is there a form that maps to the field I get an error. Do I check for write permissions of the field with the old name somewhere, I get an error. I use exhaustive matching to ensure that all cases of enums or union types in general are handled. Everything is type safe and the types come from a single source of truth.
It's so insanely productive it feels like magic!
Edit: also wanted to add I mostly do not use libraries outside of framework libs for angular or react in my frontend. Generally most library code I need (with few exceptions) is built by myself rather fast and easily. I avoid libraries because of the npm ecosystem mess but it also has the upside that I don't have problems with outdated type declarations or typescript incompatibilities.
In my company we built a lot of web apps in very small teams (mostly just 2 people). We use mostly c# as a backend and typescript + mostly angular, sometimes react as a frontend. When typescript came out I built a conversion utility that allows me to generate typescript definitions and metadata from my c# type definitions. In angular I built my own type safe reactive forms, access control and API framework. Often we use ef core as a database layer on the backend, so we have a single source of truth (the c# types) for database and frontend types for the API. I use mapped types in typescript a lot to reuse the generated API types in my frontend code. If a field in a class is renamed ef core takes care of the database migration. On the frontend I get notified of every error because of the rename. Is there a table column for the field, I get an error. Is there a form that maps to the field I get an error. Do I check for write permissions of the field with the old name somewhere, I get an error. I use exhaustive matching to ensure that all cases of enums or union types in general are handled. Everything is type safe and the types come from a single source of truth.
It's so insanely productive it feels like magic!
Edit: also wanted to add I mostly do not use libraries outside of framework libs for angular or react in my frontend. Generally most library code I need (with few exceptions) is built by myself rather fast and easily. I avoid libraries because of the npm ecosystem mess but it also has the upside that I don't have problems with outdated type declarations or typescript incompatibilities.