打字稿中的逗号是什么意思

Question

What does the , mean? Is it the same as | which is it can be either the first type or any?

CustomFieldValue<Sometype, any>

Answer 1

It's the list of type parameters - pretty similar to an argument list. Each type parameter is separated by a comma. For example, with

type CustomFieldValue<K, V> = Map<K, V>;
type mapOfStringsByNumbers = CustomFieldValue<number, string>

The first type parameter number corresponds to K, and the second type parameter string corresponds to V, so the result is the type of a Map whose keys are numbers and values are strings.

Your

CustomFieldValue<Sometype, any>

is passing two type parameters to CustomFieldValue : Sometype and any . It's not a union.

Answer 2

In your example, CustomFieldValue has two generic types one is SomeType and the other is any . A , is simply a generic type separator. You can learn more about Typescript Generics here .

An example of a class CustomFieldValue with two generic fields could be:

public class CustomFieldValue<T, K> {
    field1: T;
    field2: K;
}

Then, when you want to use it:

const myValue = new CustomFieldValue<SomeType, any>();
// myValue.field1 is of type SomeType
// myValue.field2 is of type any

A | is used to define union types, as described here