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It's a contradiction I see in this discussion quite often.

If you want "quick feedback loops", a type checker is probably one of the quickest. Almost always quicker to give feedback than tests even. And certainly quicker than ftping code to a webserver and clicking through a webapp manually.

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Modern JS (actually TS) tooling has adopted a middle ground. There is an instant feedback - un-type-checked version that runs (typically used in dev mode) with instant-feedback/hot-reload, and a slower compile and build flow that builds for production.

I was initially not very convinced of the benefits - why have a type-checker if you won't use it in the small? But IDEs provide much of the benefit inline while writing code and this is seldom a real problem from the DX perspective.

My skepticism was unwarranted.

With Python + mypy you get this middle ground as well. No need to type-check before you run your code, if you don't want to.

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