Use npm to build JavaScript assets (#656)

The npm run deploy script will build the assets based on the contents
of package.json. For older projects this will use brunch by default,
for newer projects, webpack will be used.

docs/guides/phoenix_walkthrough.md

@@ -65,10 +65,7 @@ Now we have the Phoenix app created with Distillery and our configuration all re
 ```
 $ mix deps.get --only prod
 $ MIX_ENV=prod mix compile
-$ cd assets
-$ npm install
-$ node node_modules/webpack/bin/webpack.js --mode production
-$ cd ..
+$ npm run deploy --prefix assets
 $ mix phx.digest
 ```
 
@@ -98,7 +95,7 @@ You should be able to go to [localhost:4001](localhost:4001) and load the defaul
 
 *NOTE* The above commands can be combined into one quick command as
 ```
-$ cd assets && node ./node_modules/webpack/bin/webpack.js --mode production && cd .. && MIX_ENV=prod mix do phx.digest, release --env=prod
+$ npm run deploy --prefix assets && MIX_ENV=prod mix do phx.digest, release --env=prod
 ```
 
 *NOTE*: If you run `mix release` with `MIX_ENV=dev` (the default), then you must also ensure that you set `code_reloader: false` in your configuration. If you do not, you'll get a failure at runtime about being unable to start `Phoenix.CodeReloader.Server` because it depends on Mix, which is not intended to be packaged in releases. As you won't be doing code reloading in a release (at least not with the same mechanism), you must disable this.
@@ -108,11 +105,19 @@ $ cd assets && node ./node_modules/webpack/bin/webpack.js --mode production && c
 
 If you followed the above you will have generated a working release. A few notes on some of the above commands we used:
 
-1. `node ./node_modules/webpack/bin/webpack.js --mode production` builds your assets in production mode. More detail can be found in the [Phoenix Static Asset Guide](http://phoenixframework.org/blog/static-assets)
-1. `MIX_ENV=prod mix phx.digest` To compress and tag your assets for proper caching. More detail can be found in the [Phoenix Mix Task Guide](https://hexdocs.pm/phoenix/Mix.Tasks.Phoenix.Digest.html)
-1. `MIX_ENV=prod mix release --env=prod` To actually generate a release for a production environment
+- `npm run deploy --prefix assets` builds your assets in
+   production mode. More detail can be found in the
+   [Phoenix Static Asset Guide](http://phoenixframework.org/blog/static-assets)
+- `MIX_ENV=prod mix phx.digest` To compress and tag your assets
+    for proper caching. More detail can be found in the
+    [Phoenix Mix Task Guide](https://hexdocs.pm/phoenix/Mix.Tasks.Phoenix.Digest.html)
+- `MIX_ENV=prod mix release --env=prod` To actually generate a release for a
+    production environment
 
-You might wonder "why all the hassle to build a release?" A Phoenix project in `dev` mode is supposed to be interactive with features such as live code reload and automatic `webpack` asset recompilation and extra logging. While great for development, it comes at a performance cost and you would not want to run a production Phoenix application in dev mode.
+You might wonder "why all the hassle to build a release?" A Phoenix project in `dev` mode is
+supposed to be interactive with features such as live code reload and automatic `webpack` asset
+recompilation and extra logging. While great for development, it comes at a performance cost
+and you would not want to run a production Phoenix application in dev mode.
 
 
 #### Take that Release Anywhere
@@ -174,7 +179,7 @@ Remove the following line from our application layout.
 
 Next we build an upgrade release with the following command:
 
-`cd assets && node ./node_modules/webpack/bin/webpack.js --mode production && cd .. && MIX_ENV=prod mix do phx.digest, release --env=prod --upgrade`
+`npm run deploy --prefix assets && MIX_ENV=prod mix do phx.digest, release --env=prod --upgrade`
 
 This is the same command as in version 0.0.1 with the exception of `--upgrade`. The upgrade flag tells Distillery to build an [appup](https://hexdocs.pm/distillery/guides/upgrades_and_downgrades.html) for every application included in the release. These files are then used to generate a [relup](https://hexdocs.pm/distillery/guides/upgrades_and_downgrades.html) which details how an upgrade (or downgrade) is applied to a running application instance.
 
@@ -262,10 +267,10 @@ end
 
 With all that complete, we are now ready to generate the 0.0.3 release just as we did with 0.0.2. So we will generate a release, copy the 0.0.3 tarball into a new release directory under `local_deploy`, and upgrade the application.
 
-1. `cd assets && node ./node_modules/webpack/bin/webpack.js --mode production && cd .. && MIX_ENV=prod mix do phx.digest, release --env=prod --upgrade`
-1. `mkdir local_deploy/releases/0.0.3`
-1. `cp _build/prod/rel/phoenix_distillery/releases/0.0.3/phoenix_distillery.tar.gz local_deploy/releases/0.0.3/`
-1. `./local_deploy/bin/phoenix_distillery upgrade 0.0.3`
+- `npm run deploy --prefix assets && MIX_ENV=prod mix do phx.digest, release --env=prod --upgrade`
+- `mkdir local_deploy/releases/0.0.3`
+- `cp _build/prod/rel/phoenix_distillery/releases/0.0.3/phoenix_distillery.tar.gz local_deploy/releases/0.0.3/`
+- `./local_deploy/bin/phoenix_distillery upgrade 0.0.3`
 
 If you go reload your browser and open your console you will be greeted by a series of increasing numbers from 0!
 
@@ -306,10 +311,10 @@ end
 
 With this complete, we are now ready to generate the 0.0.4 release just as we did with 0.0.3. Generate a release, copy the 0.0.4 tarball into a new release directory under `local_deploy`, and upgrade the application.
 
-1. `cd assets && node ./node_modules/webpack/bin/webpack.js --mode production && cd .. && MIX_ENV=prod mix do phx.digest, release --env=prod --upgrade`
-1. `mkdir local_deploy/releases/0.0.4`
-1. `cp _build/prod/rel/phoenix_distillery/releases/0.0.4/phoenix_distillery.tar.gz local_deploy/releases/0.0.4/`
-1. `./local_deploy/bin/phoenix_distillery upgrade 0.0.4`
+- `npm run deploy --prefix assets && MIX_ENV=prod mix do phx.digest, release --env=prod --upgrade`
+- `mkdir local_deploy/releases/0.0.4`
+- `cp _build/prod/rel/phoenix_distillery/releases/0.0.4/phoenix_distillery.tar.gz local_deploy/releases/0.0.4/`
+- `./local_deploy/bin/phoenix_distillery upgrade 0.0.4`
 
 *DO NOT RELOAD YOUR BROWSER* Simply stare at your console and wait. In no time at all you will see numbers start incrementing by 1 rather than 2. You will conclude that hot upgrades are the coolest thing since sliced bread.