Possible to extend types in Typescript?
Say I have the following type:
type Event = {
name: string;
dateCreated: string;
type: string;
}
I now want to extend this type, i.e.
type UserEvent extends Event = {
UserId: string;
}
This doesn't work. How can I do this?
type keyword is used to define type aliases, not interfaces or classes.
The keyword extends can be used for interfaces and classes only.
If you just want to declare a type that has additional properties, you can use intersection type:
type UserEvent = Event & {UserId: string}
UPDATE for TypeScript 2.2, it's now possible to have an interface that extends object-like type, if the type satisfies some restrictions:
type Event = {
name: string;
dateCreated: string;
type: string;
}
interface UserEvent extends Event {
UserId: string;
}
It does not work the other way round - UserEvent must be declared as interface, not a type if you want to use extends syntax.
And it's still impossible to use extend with arbitrary types - for example, it does not work if Event is a type parameter without any constraints.
you can intersect types:
type TypeA = {
nameA: string;
};
type TypeB = {
nameB: string;
};
export type TypeC = TypeA & TypeB;
somewhere in you code you can now do:
const some: TypeC = {
nameB: 'B',
nameA: 'A',
};
TextInputProps for my own custom text entry component. Thanks!
What you are trying to achieve is equivalent to
interface Event {
name: string;
dateCreated: string;
type: string;
}
interface UserEvent extends Event {
UserId: string;
}
The way you defined the types does not allow for specifying inheritance, however you can achieve something similar using intersection types, as artem pointed out.
interface when I actually mean a type
A generic extension type can be written as follows:
type Extension<T> = T & { someExtensionProperty: string }
Follow WeChat
Success story sharing
Want to stay one step ahead of the latest teleworks?
Subscribe Now相似问题
- How can I know which radio button is selected via jQuery?
- How do I loop through or enumerate a JavaScript object?
- How to replace all occurrences of a string in JavaScript
- What does "use strict" do in JavaScript, and what is the reasoning behind it?
- event.preventDefault() vs. return false
- How to extend an existing JavaScript array with another array, without creating a new array
- How to decide when to use Node.js?
- Interfaces vs Types in TypeScript
interface A<T> extends B<T> {blar}An interface can only extend an object type or intersection of object types with statically known membersinterface Identifiable<T> extends T { id: string }gives me error "An interface can only extend an object type or intersection of object types with statically known members.ts(2312)"