Use types annotations today, even if you don't actually use Flow (or TypeScript). Then strip the assertions in production.
Flowcheck comes with a built-in browserify transformer and supports sourcemaps for a seamless workflow integration.
You can even use Flowcheck as a general purpose validation library.
Flowcheck adds asserts for each type annotation using jstransform.
If an assert fails the debugger kicks in so you can inspect the stack and quickly find out what's wrong.
The transformer adds assertions for each type annotation.
The assertion module checks the types at runtime. If an assert fails the debugger kicks in so you can inspect the stack and quickly find out what's wrong.
There is flowcheck-loader for Webpack which is equivalent to Flowcheck's Browserify transform.