Remove section about ES modules and tree-shaking

[taion]

In practice, tree-shaking does not currently allow for the kind bundle size reduction achievable using direct module imports, so shouldn't encourage it as an option for minimizing bundle size.

@Rich-Harris explains it here: reduxjs/redux#1369 (comment).

Specifically, because of the way we set up the singleton histories, those will not tree-shaken out, as noted by @tomduncalf in #3387 (comment).

The best approach then is to import from the ES module directory, but I don't think we should encourage people to import from react-router/es6/* when we want to move that to react-router/es/*. Maybe we should maintain an ES module build in both /es and /es6.

[ryanflorence]

I'm happy to rethink the singleton histories.

They showed up because of the redux/flux people wanting to navigate inside of actions.

I still think they should just pass the router to their action and do it that way, or return a promise from the action (reduxjs/redux#61 (comment)) and then in the view navigate when the action is done: this.props.dispatch(action()).then(() => router.push(...))

[taion]

It's not just the singleton histories though, and I really do think they're a convenient pattern.

The history thing is the most noticeable example, but tree-shaking is just a fairly fragile thing right now, and doesn't work as well with top-level exports as I'd hoped.

I think it's mostly just that tree-shaking is somewhat weak in practice. I'm not even sure if it's possible to tree-shake out stuff like <Redirect> if you don't use it, since how would the bundler know that React.createClass doesn't have global side effects?

[taion]

What do we think about dropping the ES module build for v3? Given that tree-shaking isn't going to work, I don't know that it's worth keeping that extra build around.

[b2whats]

yes, tree-shaking not work with react-router

main.js

// import { browserHistory } from 'react-router/es6'; //First
// import browserHistory from 'react-router/lib/browserHistory'; //Second
console.log(browserHistory)

 bundle.js      99 kB       0  [emitted]  main // First
 bundle.js    21.3 kB       0  [emitted]  main// Second