How get convert typescript defined types of strings to array of strings

Question

I'm tryining get all defined types from variable in construct.

export interface TestType {
  resultType?: 'NUMBER' | 'STRING' | 'DATE' | 'ENUM' | 'AMOUNT' ;
}

And I expect the result of something like this.

const types: string[] = ['NUMBER', 'STRING', 'DATE', 'ENUM', 'AMOUNT'];

There may be a function or ability to achieve this from constructor. When the contrustor cannot be changed?

I try to automate it so that it basically extracts all types and I was able to get them to select.

Here is just one example that this is not possible.

Or ideas for similar solutions?

Actual I am currently using Typescript in v4.0.5

Thanks.

Simplicity's_Strength · Accepted Answer · 2021-05-31 13:44:46Z

0

If what you want is something similar to iterate over possible values of a variable. Types need to be refered to in a static final way in typescript.

export class TestClass{
    types = ['NUMBER', 'STRING', 'DATE', 'ENUM', 'AMOUNT'] as const;
    resultType: TestClass["types"][number];
}

In the above example the accepted values of resultType are members of the types Array. So type validation will trigger.

edited May 31, 2021 at 13:44

answered May 31, 2021 at 13:27

Simplicity's_Strength

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hansmaad · Accepted Answer · 2021-05-31 14:11:31Z

0

As these types do not exist at runtime, you cannot generate the strings directly. You could create some helper that will ensure that you use only the right keys.

type Types = 'foo'|'bar'|'baz';

type TypeHolder<T extends string> = { [Key in T]: number; }

function getKeys<T extends string>(types: TypeHolder<T>) {
    return Object.keys(types);
}

console.log(getKeys<Types>({ foo: 1, bar: 1, baz: 1 }));  // ['foo', 'bar', 'baz']

Hmm, not really nice. It's probably much easier to do it the other way around:

const types = ['foo', 'bar', 'baz'] as const;
type Types = typeof types[number];   // 'foo'|'bar'|'baz'

answered May 31, 2021 at 14:11

hansmaad

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