[chrisjc]

First, forgive my ignorance of the JS/TS and bundler ecosystems.

> while in parallel checking for type errors.

Why are you suggesting this not be done during development? Is it bc while ESBuild is fast and runs in parallel, it's still only as fast as the slowest parallelized task, and in this case the slowest task is checking for type errors? And I assume checking for type errors is the slowest because it has to invoke an external resource, tsc?

Would it not make sense to have two development bundlers then? One for getting your code up and running quickly, and a second that outputs a dummy build artifact, but allows a more thorough production-like build that includes type checking (or other long running activities)? That way you get all the verification you would like, but don't pay a price on waiting for your code to deploy?

[Vinnl]

You can absolutely run it during development! In fact, many people will use an editor that automatically does this and highlights any potential errors - which means you don't need your compiler to display them (or even block compiling) as well.

And yes, type checking is relatively slow, and also strictly extra work, since it's not required to make your code runnable.

You'll often see that people do still do a more thorough production build in their CI systems, but not necessarily by using a bundler that includes type checking; rather, they just run type checking and bundling as separate tasks. That way, you do indeed get all the verification you would like without having to delay deployment.

(To make it somewhat more confusing, a project like Vite does use a fast bundler (ESBuild) during development and a more thorough one for production (Rollup), but that's independent of type checking. It's more about the latter doing more optimisations, and the former merely making the code runnable by the browser.)