Create a type-safe object based on an interface in TypeScript

object-proxy.ts

// TS Playground: https://www.typescriptlang.org/play?#code/JYOwLgpgTgZghgYwgAgDIHsDmoBi6oC2OwEANgCYDOyA3gFDLICul0IcBEAXMpWFKEwNkABziVKAd3zkA-Dz4CQmANx0AvnTpgAniJR5CxMlQA8AFQB8yALy1hAaigQ45dCFI7kAbQDWEL1Bkfx10GGRzAF0AWnlggI0tGCYQBDBgd2ZWYwoAOQ4ISgtLAAoASh5DIhIKIqt7RmcwJigQZBAISWQABSh0AA8dEpp1ZHFkKpyzKwAaBsZkTAgwEoB9OZE+-ShdMvmF5CaWts30bd1hRk0rssS6BHc+ZBga8nzOajsWCCn3wtMMNgQJNXpRSrcDsgAPRQ5AAPVkSVef0oADpvq0CpdIYwYfDES8TCjUWIJNIoORsTi8Qi6IS8gU0aSyTIqZCaYj7o90KQIKjSFgSvS3oz0axMZxbnQ8QBZOAifTkCJ6FAy9DkYCEqCULjS2EACzAYBEOphknNqNCTGaACM+Q8CFDJHAwAh9bIAG42AAMAC9MAB1dCrTAgX0ANQAkkA

interface LoginFormFields {
  username: string
  password?: string;
}

type FormFields<T> = {
  // Mapped Type Modifiers:
  // https://www.youtube.com/watch?v=0zgWo_gnzVI
  +readonly [key in keyof T]-?: key
}

function useFieldNames<T>(): FormFields<T> {
  return new Proxy({} as FormFields<T>, {
    get(_, property) {
      return property
    }
  })
}

const fieldNames = useFieldNames<LoginFormFields>()
     // ^?

fieldNames.username
          // ^?
fieldNames.password
          // ^?
fieldNames.passsword
          // ^?

console.log(fieldNames.username)