Creating a TypeScript type based on the static values of a class

Question

Creating a TypeScript type based on the static values of a class

In my Market class, there is only one parameter: name.

class Market {
  name: string

  constructor(name: string) {
    this.name = name
  }
}

Next, I have a Markets class that contains a static collection of multiple markets.

class Markets {
  static M1 = new Market("M1M")
  static M2 = new Market("M2M")
  static M3 = new Market("M3M")
}

I am curious to know if it's possible to gather all the name parameters from all markets into a single type. The resulting type would resemble something like this:

type MarketNames = "M1M" | "M2M" | "M3M"

I have heard about the keyof operator - could this be the solution?

Thank you.

typescript

Answer 1

Answer №1

In order for this method to be effective, your class needs to have a generic structure so that we can later extract the generic part from it:

class Market<Name extends string> {
  name: Name;

  constructor(name: Name) {
    this.name = name
  }
}

Next, we define a type to extract the names:

type NamesOfMarkets<T> = Extract<T[keyof T], Market<string>> extends Market<infer N> ? N : never;

We are specifically filtering out only the values of the class that pertain to Markets, then inferring and returning the name.

Note: When using typeof Markets, you will obtain the constructor type. Simply using Markets alone refers to a class instance.

Check out the Playground here

Answer 2

In order for this method to be effective, your class needs to have a generic structure so that we can later extract the generic part from it:

class Market<Name extends string> {
  name: Name;

  constructor(name: Name) {
    this.name = name
  }
}

Next, we define a type to extract the names:

type NamesOfMarkets<T> = Extract<T[keyof T], Market<string>> extends Market<infer N> ? N : never;

We are specifically filtering out only the values of the class that pertain to Markets, then inferring and returning the name.

Note: When using typeof Markets, you will obtain the constructor type. Simply using Markets alone refers to a class instance.

Check out the Playground here

Creating a TypeScript type based on the static values of a class

Answer №1

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