Is it possible to dynamically check values in TypeScript?

[Summary] I am looking to dynamically expand my type in TypeScript based on an initial set of values. I want to avoid managing separate arrays/types and instead extend all strings in my type with '_max'.

type ExtendedValueTypes = 'money' | 'land' | 'money_max' | 'land_max';
// dynamically from
type ValueTypes = 'money' | 'land';

I have a list of values

const values = ['money', 'land'] as const;
type ValueTypes = typeof values[number];
// equals ValueTypes = 'money' | 'land';

Now I want to dynamically extend my type to equal

type ExtendedValueTypes = 'money' | 'money_max' | 'land' | 'land_max';

To achieve this, I need a type declaration that automatically appends '_max' to all the strings in my type definition.

const check = (type: ValueTypes) => 'some return'

//works
check('money');

// does not work but should
check('money_max')

Answer №1

If you want to manipulate string literal types, you can utilize template literal types in the following manner:

type ExtendedValueTypes = ValueTypes | `${ValueTypes}_max`
// type ExtendedValueTypes = ValueTypes | "money_max" | "land_max"


const check = (type: ExtendedValueTypes) => 'some return'

//works
check('money');

//works
check('money_max');

Link to Playground with code example

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