Building Interface/Type with Static Properties and Constructor Signature in TypeScript

Question

Building Interface/Type with Static Properties and Constructor Signature in TypeScript

I am looking to devise an interface or a type that contains static properties and a constructor signature. My goal is to utilize this interface/type as a parameter for a function. I experimented with using an interface, but encountered limitations in declaring static fields within it. I also attempted utilizing an abstract class structured as shown below:

interface IClassType {
  instanceMethod: (param: string) => void;
}

abstract class IBaseClass {
  static requiredProperty: string;
  static optionalProperty?: boolean;
  abstract new (param: number): IClassType;
}

I proceeded by attempting to apply the abstract class as a type within a function setup similar to the one outlined below:

// @param UserClass: must implement or extend IBaseClass

const demoFunction = (UserClass: IBaseClass) => {
  const demoClass = new UserClass(3); 
  // Triggers a compiler error: 
  // "Type 'IBaseClass' has no construct signatures."

  const demoProp = UserClass.requiredProperty; 
  // Triggers a compiler error:
  // "Property 'requiredProperty' does not exist on type 'IBaseClass'. 
  // Did you mean to access the static member 
  // 'IBaseClass.requiredProperty' instead?"
}

Assistance in resolving this issue would be highly valued.

typescript typescript-types

Answer 1

Answer №1

Within the context you provided, the IBaseClass type represents an instance of the abstract IBaseClass class. The type associated with the constructor of the IBaseClass class would be typeof IBaseClass, but it is not recommended to use this type since the class is abstract and cannot be instantiated.

Instead, you can define an interface that corresponds to the desired constructor type:

interface IClassTypeConstructor {
    requiredProperty: string;
    optionalProperty?: boolean;
    new(param: number): IClassType;
}

Therefore, an IClassTypeConstructor includes static properties of interest and a constructor signature that generates instances of IClassType.

By passing an object of this type to the function demoFunction(), everything should function as anticipated:

const demoFunction = (UserClass: IClassTypeConstructor) => {
    const demoClass = new UserClass(3); // works fine
    demoClass.instanceMethod("abc"); // works fine
    const demoProp = UserClass.requiredProperty; // works fine
}

Link to Playground for code testing

Answer 2

Within the context you provided, the IBaseClass type represents an instance of the abstract IBaseClass class. The type associated with the constructor of the IBaseClass class would be typeof IBaseClass, but it is not recommended to use this type since the class is abstract and cannot be instantiated.

Instead, you can define an interface that corresponds to the desired constructor type:

interface IClassTypeConstructor {
    requiredProperty: string;
    optionalProperty?: boolean;
    new(param: number): IClassType;
}

Therefore, an IClassTypeConstructor includes static properties of interest and a constructor signature that generates instances of IClassType.

By passing an object of this type to the function demoFunction(), everything should function as anticipated:

const demoFunction = (UserClass: IClassTypeConstructor) => {
    const demoClass = new UserClass(3); // works fine
    demoClass.instanceMethod("abc"); // works fine
    const demoProp = UserClass.requiredProperty; // works fine
}

Link to Playground for code testing

Building Interface/Type with Static Properties and Constructor Signature in TypeScript

Answer №1

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