Define keys type for object from array

Question

I need to make the variable TYPES_GENERATED have the type that it has keys that in the array TYPES_ARR with symbol values.

const TYPES_ARR = [
  'HttpClient',
  'Parser'
]
const TYPES_GENERATED = {}

TYPES_ARR.forEach(i => {
  TYPES_GENERATED[i] = Symbol.for(i)
})

I do not want to write:

const TYPES_GENERATED: {
  HttpClient: symbol
  Parser: symbol
} = {}

I took the code above from here.

Is there a way to do this? I can use the latest version of the TypeScript.

Answer 1

My suggestion would be to use a const assertion to allow the compiler to keep track of the specific string literal values in TYPES_ARR, and then to assert that TYPES_GENERATED is a mapped type (such as the built-in Record<K, V>) having keys from the elements of TYPES_ARR and values of type symbol:

const TYPES_ARR = ["HttpClient", "Parser"] as const;
const TYPES_GENERATED = {} as Record<typeof TYPES_ARR[number], symbol>;
TYPES_ARR.forEach(i => {
  TYPES_GENERATED[i] = Symbol.for(i);
});

Hope that helps; good luck!

Link to code