Is it possible for me to achieve this elementof?

Question

Is it possible for me to achieve this elementof?

My goal is to achieve the following:

const names = ["foo", "bar", "baz"];
type NameType = elementof names;  // This is an invalid TypeScript syntax

The desired outcome should mirror the behavior of this code:

type NameType = "foo" | "bar" | "baz";

To solve this, we need a solution that can:

Create a list of strings in a specific order.
Allow easy access to individual string literals.
Enable updating string values without needing to modify the source code repeatedly.

Is it possible for TypeScript to meet these requirements?

Please note: This question differs from the query about Converting string[] literal to string type literal as it specifically calls for maintaining the order of strings. Union types do not provide runtime order information.

typescript

Answer 1

Answer №1

To determine the type of an item, you can utilize a type query method:

type NameType = typeof names[number];

An issue arises when attempting to retrieve the type of names, which is initially defined as string[]. Consequently, the aforementioned code snippet will only yield string.

Alternatively, you can deduce the string literal types for the const using a supporting function.

function array<T extends string>(items: T[]) : T[] {
  return items
}

const names = array(["foo", "bar", "baz"]);
type NameType = typeof names[number];   // Resolves to "foo" | "bar" | "baz"

Answer 2

To determine the type of an item, you can utilize a type query method:

type NameType = typeof names[number];

An issue arises when attempting to retrieve the type of names, which is initially defined as string[]. Consequently, the aforementioned code snippet will only yield string.

Alternatively, you can deduce the string literal types for the const using a supporting function.

function array<T extends string>(items: T[]) : T[] {
  return items
}

const names = array(["foo", "bar", "baz"]);
type NameType = typeof names[number];   // Resolves to "foo" | "bar" | "baz"

Is it possible for me to achieve this elementof?

Answer №1

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