Upgrade to Babel 7

[amithgeorge]

This will primarily focus on upgrading Babel 7 in quintype/build.

Babel configs

We have to manage babel configs for three environments - server, client and test. For most part the test configuration should be the same as the server configuration.

On server side code, we need babel to

• transpile the code as per the running NodeJS version
• transform ES modules to CJS modules
• transform any dynamic imports
• replace import of assets with a static string
• let css module classes be generated and added to markup

On client side code, we need babel to

• transpile code as per some browserlist config
• keep ES modules as is, let webpack handle it
• keep dynamic imports as is, let webpack handle it

To enable better development workflow, we want the server code to be transpile on the fly. This is demonstrated in index.js

In production mode, we don't want on the fly transpilation. Instead we want to overwrite the src files with the transpiled ones during the Docker image build stage.

Places where babel config is currently defined

• index.js (server dev time)
• default-babel-rc (server prod time)
• bin/quintype-build (server prod time)
• webpack.config.js (client)

Requirements of new babel/webpack configs

• should allow running only babel on the server code
• should support BABEL_TARGET and NODE_ENV to allow generating config for browser/server and dev/prod combinations
• should be able override babel config via app specific JS
• should be able override webpack config via app specific JS
• should be able to pass it to jest/mocha with necessary options set
• should be able to get entire babel/webpack config as a JS object to easily merge it with storybook config

For Jest (tests),

• Use a custom transformer file to give the path of babel config

For Babel Register (server side, dev mode),

• It directly accepts the path to the config file

For Babel CLI (server side, prod mode),

• It directly accepts the path to the config file

For Webpack (browser, prod & dev mode)

• Babel Loader can be given the path to the babel config file.
• Babel Loader can also accept the entire babel config as an object

Steps,

• The babel config file is loaded
• It will read environment variables BABEL_TARGET and NODE_ENV to determine if config is for server/browser and prod/dev.
• It will read the quintype-build.config.js file if present in the application root, ie the working directory.
• The file will export build options object. It can have functions like modifyBabel, modifyWebpack to allow the developer to customize the babel/webpack config.
• The default config is prepared based on environment variables and then passed to modifyBabel for augmentation. The returned config is exported.

[amithgeorge]

Initial PR for the same - quintype/quintype-node-build#12