reagent/docs/0.8-upgrade.md

# 0.8 Upgrade guide

The necessary changes depend on what environment you target, and
how you want to provide React.

|                | Build       | Browser       | Node |
|---|---|---|---|
| Cljsjs         | `:none`     | Supported     | Requires Cljs 1.10.238+ |
| Cljsjs         | `:advanced` | Supported     | Requires Cljs 1.10.238+ |
| `node modules` | `:none`     | Known problems (1)     | Supported  |
| `node modules` | `:advanced` | Known problems (2)     | Supported  |

While Reagent 0.8 supports use with React from npm, there are known problems:

1. Closure can't properly handle React 16 CommonJS module pattern: https://github.com/google/closure-compiler/issues/2841
This causes the production React code being loaded even for development builds.
Using Chrome React Developer Tools with this setup will break Reagent.

2. Closure optimization currently breaks certain statically created objects which are
accessed dynamically in `ReactDOM/server`: https://github.com/facebook/react/issues/12368
Fixed by using `[com.google.javascript/closure-compiler-unshaded "v20180319"]` ([fix commit](https://github.com/google/closure-compiler/commit/c13cf48b98477e44409dba6359246bffa95b1c7b)), will be
the default in next ClojureScript release.

## Browser - Cljsjs

**This is the recommended setup.**

Using Reagent with Cljsjs packages doesn't require changes,
other than making sure you update Cljsjs React dependencies,
if you have direct dependencies to them.

To ensure Cljsjs libs are used instead of Node Modules, you can add `:npm-deps false`, which will make sure ClojureScript compiler doesn't look into `node_modules` directory if it exists.

## Browser - node modules

If `react`, `react-dom` and `create-react-class` are available in `node_modules`
directory, ClojureScript compiler will use these with Reagent.

If you don't want to call `npm` and manage `package.json`, you can use `:npm-deps` and `:install-deps` compiler options to
have ClojureScript install the packages automatically.

You can use `:process-shim` compiler option to provide `process.env.NODE_ENV`
constant which is used by JS code to enable development and production
builds. ClojureScript compiler will automatically set this constant to
`production` value when using `:advanced` optimizations. This enables
the React production build.

When using module processing, it should be possible to split output into several
[modules](https://clojurescript.org/reference/compiler-options#modules).

**Externs are required for use with node modules also!** React created objects
statically in several places and then accesses those dynamically. Closure-compiler
will in these cases rename the statically object properties, which will break
dynamically accessing the objects. Externs fix this by defining which properties
must not be renamed.

## Browser - loading React from CDNJS or custom Webpack bundle

**TODO: Not tested properly**

If you want to load React.js yourself from external JS file (CDN) or from custom bundle,
it should be possible to override the Cljsjs foreign-libs, while still using externs from Cljsjs packages. To override the foreign-libs, you can provide following compiler option:

```clj
:foreign-libs
 [{:file "empty.js",
   :provides ["react" "react-dom" "create-react-class" "react-dom/server"],
   :requires [],
   :global-exports {react React
                    react-dom ReactDOM
                    create-react-class createReactClass
                    react-dom/server ReactDOMServer}}]
```

You'll also need to create the mentioned `empty.js` file (FIXME: relative to `project.clj`?).

If your bundle provides other libraries, you could extern `:provides` and `:global-exports` (e.g. `prop-types`).

## NodeJS - Cljsjs

Requires https://github.com/clojure/clojurescript/commit/f7d611d87f6ea8a605eae7c0339f30b79a840b49

Available in 1.0.238

Reagent should use Cljsjs libraries by default even when running on Node.

## NodeJS - node modules

Install `react`, `react-dom` and `create-react-class` npm packages,
and ClojureScript should automatically use `require` to
load React for Reagent.

## Electron

???

## React-native

https://github.com/drapanjanas/re-natal/issues/128

## Common Problems

### Mismatch with Cljsjs and npm packages

If you have one npm package installed, e.g. `react`, you also need
to provide others (`react-dom` and `create-react-class`), else
Cljsjs packages would be used for these, and packages from different sources
don't work together.