The Build Process
By now you should be able to build Phaser 3, run the examples, and create new examples. So it's time to explain the build process briefly.
When you issue the command webpack it will load up the webpack.config.js into webpack, and execute everything in there.
It uses the WebpackShellPlugin to run some Node.js scripts, pre and post build. The first thing it does is run node create-checksum.js. This outputs the file src/checksum.js which contains version and checksum data. You can use the checksum in the examples to ensure you're testing against the correct version.
Webpack then runs its main process. At the time of writing it uses the file src/phaser.js as its entry point. This is the standard 'everything and the kitchen sink' version of Phaser. Over time we'll create smaller, more focused packages too.
Once the build has run, assuming no errors, it runs the post-build node script copy-to-examples.js which pretty much does what it says on the tin. It literally copies the freshly built phaser.js file from the dist folder to the phaser3-examples/public/js/ folder.
Because of the way the Example Runner works (by reloading an iframe) it means you can have the Example Sandbox open in your browser, write some code, Run it, re-build Phaser, and just run the example code again (without having to do anything else first) and it'll instantly be running the latest build. This is a really quick way to iterate and test during development.
Webpack has a lot of other features, such as source map generation and production (minified) outputs, but for the sake of Phaser 3 development that is all we need for now. If you've any suggestions on how to improve the build process, then please let us know.