[i_like_robots]

> Webpack's loaders can't really check your types because, without doing a lot of extra magic, they operate on one file at a time.

This is the point folks really must understand when setting up a new tooling pipeline to deal with TypeScript. Certainly all of the module bundlers I'm aware of operate in this way.

To explain further for anyone curious; for TSC to work effectively it must construct and understand the entire "compilation". To do this it starts by performing a glob match (according to your include/exlude rules) to find every TypeScript file within the project. Resolving and type checking the entire compilation every time the bundler calls for a transform on a file is very slow due to lots of repeated and unnecesssary work so most TS bundler plugins have to work around this. Unfortunately, they're still relatively slow so type checking and bundling code separately is often the best way to go.

[Nathanba]

But in theory type checks could be cached too. Why this isn't currently done is because it's probably more work and requires very deep knowledge of the typescript language and parsing. Meanwhile the bundling itself is a simple affair of combining text files together. So these tools instead just fork the typechecker for some minor gain but in practice you could absolutely cache type information. That's what every IDE does with their intellisense database. I think in this thread we are essentially talking back and forth over the current state of bundlers and most here rationalize why it's okay (if not better!) for type checking to be separated from the compilation but the reality is that it's a fairly arbitrary state of affairs. It could easily all be efficient so that type checking is just as parallelized and incremental as bundling and therefore requires no separation into a different process. As we know, after all a binary produced by c++, rust or c# is also a "bundle".

Actually this painfully reminds me why I found it so weird that tsc doesn't simply offer bundling itself. Why wouldn't it? It should be very easy for the compiler to do this as it has all the information and on top of that, tsc also has an incremental mode already. That definitely means 'incremental' for type information.

[pas]

tsc already has incremental mode, also there's the LSP, the bundler in watch mode could keep a persistent TS language server running. if the typecheck succeeds the bundler emits the new bundle, easy peasy.

If I remember correctly gulp(js) was perfectly able to do this.