Category: TypeScript

Sometimes, we want to fix the "Props with type Object/Array must use a factory function to return the default value." error with Vue.js.

In this article, we’ll look at how to fix the "Props with type Object/Array must use a factory function to return the default value." error with Vue.js.

How to fix the "Props with type Object/Array must use a factory function to return the default value." error with Vue.js?

To fix the "Props with type Object/Array must use a factory function to return the default value." error with Vue.js, we should set the default property to a function that returns an object or an array.

For instance, we write

<script>
export default {
  //...
  props: {
    exampleDefaultObject: {
      type: Object,
      default: () => ({}),
    },
    exampleDefaultArray: {
      type: Array,
      default: () => [],
    },
  },
  //...
};
</script>

to register the exampleDefaultObject and exampleDefaultArray props.

And we set the default property to a function that returns an object and an array to use the returned values as default values of the props.

Conclusion

To fix the "Props with type Object/Array must use a factory function to return the default value." error with Vue.js, we should set the default property to a function that returns an object or an array.

Sometimes, we want to get argument types for a constructor or class with TypeScript.

In this article, we’ll look at how to get argument types for a constructor or class with TypeScript.

How to get argument types for a constructor or class with TypeScript?

To get argument types for a constructor or class with TypeScript, we can use the ConstructorParameters type with the typeof operator.

For instance, we write

type C = ConstructorParameters<typeof SomeClass>;

to create type C with ConstructorParameters and typeof.

We use typeof to get the data type for the SomeClass class.

And then we can use the returned type to get the type of the constructor parameters with ConstructorParameters and assign the returned type to C.

Conclusion

To get argument types for a constructor or class with TypeScript, we can use the ConstructorParameters type with the typeof operator.

Sometimes, we want to add types for Axios response with React and TypeScript.

In this article, we’ll look at how to add types for Axios response with React and TypeScript.

How to add types for Axios response with React and TypeScript?

To add types for Axios response with React and TypeScript, we can set the type when we call an axios method.

For instance, we write

interface User {
  id: number;
  firstName: string;
}

to define the User interface.

Then we call axios.get and set response body type to a User array by writing

const { data } = await axios.get<User[]>("http://localhost:8080/admin/users");

in an async function.

User[] is the type of the response body return by the promise of axios.get.

Conclusion

To add types for Axios response with React and TypeScript, we can set the type when we call an axios method.

Sometimes, we want to allow image import with TypeScript.

In this article, we’ll look at how to allow image import with TypeScript.

How to allow image import with TypeScript?

To allow image import with TypeScript, we can use declare to declare the type for image files.

For instance, we write

declare module "*.png" {
  const value: any;
  export = value;
}

to declare the type for modules with the .png extension.

We just allow any property to be exported with

const value: any;
export = value;

And then we can import .png files without errors.

Conclusion

To allow image import with TypeScript, we can use declare to declare the type for image files.

Sometimes, we want to extend an enum in Typescript.

In this article, we’ll look at how to extend an enum in Typescript.

How to extend an enum in Typescript?

To extend an enum in Typescript, we can combine the 2 enums into a union type.

And then we can use the spread operator to spread the enum entries into a new object.

For instance, we write

enum Color1 {
  Red = "Red",
  Green = "Green",
}

enum Color2 {
  Yellow = "Yellow",
  Blue = "Blue",
}

type Colors = Color1 | Color2;
const Colors = { ...Color2, ...Color1 };

to create the Color1 and Color2 enums.

Then we create a union type between them and assign it to Colors.

Next, we create an object by spreading Color2 and Color1 into a new object and assign it to Colors.

Conclusion

To extend an enum in Typescript, we can combine the 2 enums into a union type.

And then we can use the spread operator to spread the enum entries into a new object.