Typescript: Expanding the Horizons of {}

Question

Consider the following:

class A<T extends {
  [k: string]: any
}> {
  private model: T

  constructor(model: T = {}) {
    this.model = model
  }
}

Why am I receiving an error message that states

Type '{}' is not assignable to type 'T'.

Isn't {} assignable to

{ [k: string]: any }

Appreciate your help.

Answer 1

Answer №1

This is a legitimate mistake.

Your teaching implies that this snippet is valid:

type MyType = {
    a: string;
    b: number;
}

const c = new A<MyType>();

However, upon closer inspection, the A now has a model value that is missing the necessary a and b properties.

Answer 2

This is a legitimate mistake.

Your teaching implies that this snippet is valid:

type MyType = {
    a: string;
    b: number;
}

const c = new A<MyType>();

However, upon closer inspection, the A now has a model value that is missing the necessary a and b properties.

Answer 3

The problem is outlined here. The resolution for this problem can be seen below

class A<T extends {
    [k: string]: any
}> {
    private model: T

    constructor(model: T = <T>{}) {
        this.model = model
    }
}

It is crucial to use type casting in the constructor model: T = <T>{}

Now, you can create an instance of class A like this

var instA = new A();
// instA.model will be {}

You may also want to check out this for more information. It contains links and discussions related to similar issues.

Answer 4

The problem is outlined here. The resolution for this problem can be seen below

class A<T extends {
    [k: string]: any
}> {
    private model: T

    constructor(model: T = <T>{}) {
        this.model = model
    }
}

It is crucial to use type casting in the constructor model: T = <T>{}

Now, you can create an instance of class A like this

var instA = new A();
// instA.model will be {}

You may also want to check out this for more information. It contains links and discussions related to similar issues.