I have a list
export const list = [
{
name: 'parentTitle',
},
{
name: 'anotherTitle',
},
{
name: 'whatever',
},
];
Now I want to create dynamically a union type which describes the following:
type Title = 'parentTitle' | 'anotherTitle' | 'whatever';
Is there a way to do this?
I tried to adapt the idea here: Keyof nested child objects But I can't figuring it out
The type of list in your example gets inferred by the compiler to be Array<{name: string}>, and thus the compiler has completely forgotten the particular string literal types of the name properties by the time you try to define Title.
You'll have to change how you assign list, at least somewhat. The easiest thing to do (which may or may not meet your needs) is to use a const assertion, which asks the compiler to infer the narrowest type possible:
export const list = [
{ name: 'parentTitle', },
{ name: 'anotherTitle', },
{ name: 'whatever', },
] as const;
Now list is inferred to be of type:
/*
const list: readonly [
{ readonly name: "parentTitle";},
{ readonly name: "anotherTitle";},
{ readonly name: "whatever";}
]
*/
which is a readonly tuple of readonly objects with particular name properties in a particular order. From that we can use lookup types to define Title:
type Title = typeof list[number]["name"];
// type Title = "parentTitle" | "anotherTitle" | "whatever"
Okay, hope that helps; good luck!
as const as you suggested. Is there a way to do this with a list from a json file? import list from './list.json'; type Title = typeof list[number]['name'];
as const, but it's not implemented yet.You can do as this:
type GetNameFromList<T extends readonly {name: string}[]> = T[number]['name'];
const list = [
{
name: 'parentTitle',
},
{
name: 'anotherTitle',
},
{
name: 'whatever',
},
] as const;
//here is what you want
type values = GetNameFromList<typeof list>; // 'parentTitle' | 'anotherTitle' | 'whatever'
You can make an interface for it and make an array type from it.
interface Title {
name: 'parentTitle' | 'anotherTitle' | 'whatever';
}
let list: Title[] = [
{
name: 'parentTitle',
},
{
name: 'anotherTitle',
},
{
name: 'whatever',
},
];
