TypeScript Patterns in a functional approach

builder.ts

type ShallowObject = Record<string, string | number | boolean>

type User = Partial<{
  name: string
  email: string
}> & ShallowObject

type UserBuilder = {
  addName: (name: string) => UserBuilder
  addEmail: (email: string) => UserBuilder
  addProperties: (properties: ShallowObject) => UserBuilder
  build: () => User
}

function buildUser(): UserBuilder {
  let user: User = {}

  const buildTools: UserBuilder = {
    addName(name: string) {
      user.name = name
      return buildTools
    },
    addEmail(email) {
      user.email = email
      return buildTools
    },
    addProperties(properties: ShallowObject) {
      user = { ...user, ...properties }
      return buildTools
    },
    build: () => user,
  }

  return {
    addName: buildTools.addName,
    addEmail: buildTools.addEmail,
    addProperties: buildTools.addProperties,
    build: buildTools.build,
  }
}

const loremIpsum = buildUser()
  .addName('Lorem Ipsum')
  .addEmail('lipsum@gmail.com')
  .addProperties({ age: 1742, isRandomText: true })
  .build()