I want to create a class type for classes with certain properties. E.g.:
class Cat {
name = 'cat';
}
class Dog {
name = 'dog';
}
type Animal = ???;
function foo(AnimalClass: Animal) {
console.log((new AnimalClass()).name);
}
I want doSomething to accept any class that has a string name property. The only way I could do this is:
class _Animal {
name: string;
}
type Animal = typeof _Animal;
Is there a way to do this without defining a new JS class? I just want the type.
You can describe constructor using new expression:
type AnimalContructor = new () => { name: string };
function foo(AnimalClass: AnimalContructor) {
console.log((new AnimalClass()).name);
}
Other option is defining union of constructors:
type AnimalContructor = typeof Cat | typeof Dog;
new () => {} syntax, is it possible to use extends? E.g. if Dog and Cat both extend a third-party library class, I want Animal to extend the same class. I tried something like type AnimalConstructor = new () => { name: string; prototype: Foo.prototype }; but that didn't work
type AnimalContructor = new () => { name: string } & Foo; typescriptlang.org/play?#code/…
What you can do is to use generics here. I create a type that I make this type to be only assignable to object with name property as a string, and then I add a generic type that extends Animal type. This way you don't have to create a new class for Animal.
class Cat {
name = "cat";
age = 2;
}
class Dog {
name = 'dog';
}
class Car {
brand = "Audi";
}
type Animal = {name: string};
function doSomething<T extends Animal>(animal: T) {
}
doSomething(new Dog());
doSomething(new Cat());
doSomething(new Car()); // typescript error car is missing nameAnd if you would like to make Animal type extend another class you can use intersection
class Cat {
name = "cat";
age = 2;
}
class Information {
year = 2020;
}
class Dog extends Information {
name = 'dog';
}
type Animal = { name: string } & Information;
function doSomething<T extends Animal>(animal: T) {
}
doSomething(new Dog());
doSomething(new Cat()); // typescript error cat is missing year