TypeScript: Extracting keys from stylex.defineVars

[sumanbh]

Is there a built-in type in stylex that helps us extract keys from stylex.defineVars?

Given this example:

const test = stylex.defineVars({
  primary: 'red',
  secondary: 'blue',
});

Using TS's keyof typeof x results in this type (not ideal):

type TestToken = keyof typeof test;

// type TestToken = "__opaqueId" | "__tokens" | typeof Symbol.toPrimitive | typeof Symbol.toStringTag | "primary" | "secondary" | "description" | "valueOf" | "toString"

We can manually exclude stylex's internal properties but I was wondering if there's a more elegant solution:

type TestToken = Exclude<
  keyof typeof test,
  | '__opaqueId'
  | '__tokens'
  | 'description'
  | 'valueOf'
  | 'toString'
  | typeof Symbol.toPrimitive
  | typeof Symbol.toStringTag
>;

// type TestToken = "primary" | "secondary"

[nmn]

The '__opaqueId' and '__tokens' keys are an unfortunate requirement to make all the features work in TypeScript. Since TypeScript lacks support for opaque types this was needed to make this work.

A utility type to extract just the real keys from the object is easy to make, but I can't think of any use-cases where you would be able to use it. All usage of variables defined with defineVars has to be imported by name, directly from the module where they defined and then all keys have to be defined statically as well.

Any usage of the type test[someVar] are not allowed since the usages of the variables have to be known statically at compile time.

Please tell me your use-case in case you have something in mind that would work.

In any case, here's the utility type that would work:

type TActualKeys<T> = 
  T extends string ?
    T extends '__opaqueId' | '__tokens' ?
      never
    : T
  : never;

type VarGroupKeys<G extends VarGroup> = TActualKeys<keyof G>;

type TestToken = VarGroupKeys<typeof test>;

[neighborhood999]

Here is my solution:

import type * as stylex from '@stylexjs/stylex';

export type ExtractStylexVarKeys<T> =
  T extends stylex.VarGroup<infer K> ? keyof K : never;