After finding inspiration in the detailed explanation provided in Typescript Docs on Distributive Conditional Types, I successfully adapted and implemented the concept:
https://i.sstatic.net/P96oO.png
The following code snippet showcases my adaptation, which effectively accomplishes the intended functionality:
interface SOME_OBJECT {
title: string,
label: string,
someBool: boolean,
someDate: Date,
someNumber: number
}
type ExtractStringPropertyNames<T> = {
[K in keyof T]: T[K] extends string ? K : never
}[keyof T]
type STRING_KEYS = ExtractStringPropertyNames<SOME_OBJECT>
https://i.sstatic.net/NF0Tf.png
Explore this concept in Typescript playground
If there are alternative methods or more straightforward approaches to achieving the same outcome, I am eager to learn and explore them further. The current implementation might seem like a workaround, as it lacks clarity in explaining its purpose.
UPDATE (INSIGHT INTO THE PROCESS)
Upon deeper examination to comprehend the underlying functionality of the code, I have managed to break it down into two distinct steps:
STEP 1
Initially, a new object/type is constructed based on the keys from the generic type T (SOME_OBJECT in this instance).
For each property key K, the corresponding value is evaluated to determine if it extends the type string. If so, the key name is retained as the value; otherwise, it is set to never. The result can be seen in STEP_1_RESULT.
https://i.sstatic.net/gk7jr.png
STEP 2
In this phase, we utilize the object generated from step 1 to retrieve all possible values by defining
type STEP_2<T> = T[keyof T]
.
Since keyof T represents the union of all properties within T, Typescript returns a union containing all potential values for the STEP_1_RESULT object when called with members of the keyof T union.
Ultimately, redundant never types are eliminated from the union, leaving us with
"title" | "label"
, as demonstrated in our example.
https://i.sstatic.net/Dj0II.png