Typescript: Generate types from an object

Question

I just started learning Typescript and need some help with this example.

 const alphabet = { 'a': {lower: 97, upper: 65}, 'b': {lower: 98, upper: 66} } type Char = 'a' | 'b' function printSome(char: Char){ console.log(alphabet[char]) } 

Instead of manually updating the Char type, I'd like to dynamically update generate types from the alphabet object.

Answer 1

You could use the keyof and typeof operators:

const alphabet = { 'a': {lower: 97, upper: 65}, 'b': {lower: 98, upper: 66} } type Char = keyof typeof alphabet; function printSome(char: Char){ console.log(alphabet[char]) } 

This basically turns alphabet into a type and then gets the keys of that type.