0 info it worked if it ends with ok
1 verbose cli [ '/usr/bin/nodejs', '/usr/local/bin/npm', 'run', 'dev' ]
2 info using [email protected]
3 info using [email protected]
4 verbose run-script [ 'predev', 'dev', 'postdev' ]
5 info lifecycle @~predev: @
6 silly lifecycle @~predev: no script for predev, continuing
7 info lifecycle @~dev: @
8 verbose lifecycle @~dev: unsafe-perm in lifecycle true
9 verbose lifecycle @~dev: PATH: /usr/local/lib/node_modules/npm/bin/node-gyp-bin:/opt/lampp/htdocs/laravel-mix-example/node_modules/.bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
10 verbose lifecycle @~dev: CWD: /opt/lampp/htdocs/laravel-mix-example
11 silly lifecycle @~dev: Args: [ '-c',
11 silly lifecycle 'cross-env NODE_ENV=development webpack --watch --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js' ]
12 silly lifecycle @~dev: Returned: code: 1 signal: null
13 info lifecycle @~dev: Failed to exec dev script
14 verbose stack Error: @ dev: cross-env NODE_ENV=development webpack --watch --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js
14 verbose stack Exit status 1
14 verbose stack at EventEmitter. (/usr/local/lib/node_modules/npm/lib/utils/lifecycle.js:279:16)
14 verbose stack at emitTwo (events.js:87:13)
14 verbose stack at EventEmitter.emit (events.js:172:7)
14 verbose stack at ChildProcess. (/usr/local/lib/node_modules/npm/lib/utils/spawn.js:40:14)
14 verbose stack at emitTwo (events.js:87:13)
14 verbose stack at ChildProcess.emit (events.js:172:7)
14 verbose stack at maybeClose (internal/child_process.js:821:16)
14 verbose stack at Process.ChildProcess._handle.onexit (internal/child_process.js:211:5)
15 verbose pkgid @
16 verbose cwd /opt/lampp/htdocs/laravel-mix-example
17 error Linux 4.4.0-57-generic
18 error argv "/usr/bin/nodejs" "/usr/local/bin/npm" "run" "dev"
19 error node v4.2.6
20 error npm v4.0.5
21 error code ELIFECYCLE
22 error @ dev: cross-env NODE_ENV=development webpack --watch --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js
22 error Exit status 1
23 error Failed at the @ dev script 'cross-env NODE_ENV=development webpack --watch --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js'.
23 error Make sure you have the latest version of node.js and npm installed.
23 error If you do, this is most likely a problem with the package,
23 error not with npm itself.
23 error Tell the author that this fails on your system:
23 error cross-env NODE_ENV=development webpack --watch --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js
23 error You can get information on how to open an issue for this project with:
23 error npm bugs
23 error Or if that isn't available, you can get their info via:
23 error npm owner ls
23 error There is likely additional logging output above.
24 verbose exit [ 1, true ]

This looks interesting!
I would really like a peek inside current Laravel 5.3's elixir's webpack magic and it seems like this repo sheds some light on it.
Please update the readme with more info.

I followed the steps to install and run the example but got the following errors when I ran
npm run dev

> @ dev /Users/steve/devapps/sandbox/laravel-mix-example
> cross-env NODE_ENV=development webpack --watch --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js

/Users/steve/devapps/sandbox/laravel-mix-example/node_modules/laravel-mix/src/index.js:1
(function (exports, require, module, __filename, __dirname) { let path = require('path');
                                                              ^^^

SyntaxError: Block-scoped declarations (let, const, function, class) not yet supported outside strict mode
    at exports.runInThisContext (vm.js:53:16)
    at Module._compile (module.js:387:25)
    at Object.Module._extensions..js (module.js:422:10)
    at Module.load (module.js:357:32)
    at Function.Module._load (module.js:314:12)
    at Module.require (module.js:367:17)
    at require (internal/module.js:16:19)
    at Object.<anonymous> (/Users/steve/devapps/sandbox/laravel-mix-example/node_modules/laravel-mix/setup/webpack.config.js:3:11)
    at Module._compile (module.js:413:34)
    at Object.Module._extensions..js (module.js:422:10)

npm ERR! Darwin 16.3.0
npm ERR! argv "/usr/local/bin/node" "/usr/local/bin/npm" "run" "dev"
npm ERR! node v5.8.0
npm ERR! npm  v3.7.3
npm ERR! code ELIFECYCLE
npm ERR! @ dev: `cross-env NODE_ENV=development webpack --watch --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the @ dev script 'cross-env NODE_ENV=development webpack --watch --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js'.
npm ERR! Make sure you have the latest version of node.js and npm installed.
npm ERR! If you do, this is most likely a problem with the  package,
npm ERR! not with npm itself.
npm ERR! Tell the author that this fails on your system:
npm ERR!     cross-env NODE_ENV=development webpack --watch --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js
npm ERR! You can get information on how to open an issue for this project with:
npm ERR!     npm bugs
npm ERR! Or if that isn't available, you can get their info via:
npm ERR!     npm owner ls
npm ERR! There is likely additional logging output above.

npm ERR! Please include the following file with any support request:
npm ERR!     /Users/steve/devapps/sandbox/laravel-mix-example/npm-debug.log

I tried, everything worked fine except it did not create the manifest.json file in public folder.

I tried npm run dev and npm run webpack both but was no luck.
I am on windows(node version 6.9.3).

I have webpack.mix.js file as folllows.
mix.js('resources/assets/js/back.js', 'public/js')
.sass('resources/assets/sass/back.scss', 'public/css')
.version();