balanza

"scripts":{
  "start": "http-server ./dist -p4000",
  "build": "node ./bin/build.js"
}

balanza

# install dependencies the first time
npm install less http-server handlebars
# build the website
npm run build
# serve files via http
npm start

balanza

pipelines:
  default:
    - step:
        name: Build
        image: node:10
        script:
          - npm install
          - npm run build
        artifacts:
          - dist/**

balanza

type Mobile {
  confirmed: boolean,
  value: string
}

type User {
  /* name, surname, etc */
  mobile: Mobile
}

balanza

type Valued<T> = { value: T }
type ConfirmedMobile = Valued<string> & { status: 'confirmed' } 
type UnconfirmedMobile = Valued<string> & { status: 'unconfirmed' }    
type Mobile = ConfirmedMobile | UnconfirmedMobile
type User {
  /* name, surname, etc */
  mobile: Mobile
}

// an user with confirmed mobile

balanza

// optimistic implementation: assume mobile.status will only have those two values
const printMobile = (mobile: Mobile) => {
  if(mobile.status === 'confirmed') {
    console.log('Your mobile is confirmed!')
  } else {
    console.warn('Your mobile is not confirmed!')
  }
}

// defensive implementation: assume mobile.status can be whatever

balanza

// add this line
type CertifiedMobile = Valued<string> & { status: 'certified' }   

// add CertifiedMobile to the unon type
type Mobile = ConfirmedMobile | UnconfirmedMobile | CertifiedMobile

balanza

const certified: CertifiedMobile = { status: 'certified', value: '543234531' }

printMobile(certified) // warn: Your mobile is not confirmed!

printMobileAlternative(certified) // unhandled exception: illegal state! mobile.status=certified

balanza

const exhaustionCheck = (e: never) => console.log('this will never be executed')

const printMobileSafe = (mobile: Mobile) => {
  if(mobile.status === 'confirmed') {
    console.log('Your mobile is confirmed!')
  } else if(mobile.status === 'unconfirmed') {
    console.warn('Your mobile is not confirmed!')
  } else {
    exhaustionCheck(mobile) // <-- you'll get a compilation error here!
  }

balanza

type ConfirmedMobile = string
type UnconfirmedMobile = string
type CertifiedMobile = string
type Mobile =  // just string :(
    ConfirmedMobile 
    | UnconfirmedMobile 
    | CertifiedMobile