function foo(val /* : boolean */) /* : string */ {}
function bar(x) /* : string */ {
$ npm install --save-dev babel-plugin-transform-flow-strip-types
{ plugins: ["transform-flow-strip-types"] }
$ npm install --save-dev eslint-plugin-flowtype-errors
{ plugins: ["flowtype-errors"] }
$ npm install babel-cli
$ babel src -d lib
$ npm install babel-cli babel-preset-es2015
$ echo '{ presets: ["es2015"] }' >> .babelrc
$ babel src -d lib
This means that you have the language designers themselves maintaining some of the most important crates in the ecosystem, and baking it into their process to iterate on the language itself. The result is really high quality crates and the community is better for it.
I'm not trying to dunk on JavaScript/npm packages though, or anyone involved in developing the language. Clearly the JS community has found success and is meeting a lot of people's needs. We can accept that Rome's requirements are different than most people using JavaScript.