Located at line 60359 of this specific type definition file, there is the following declaration:
type ActivatedEventHandler = (
ev: Windows.ApplicationModel.Activation.IActivatedEventArgs
& WinRTEvent<any>
) => void;
How is the & symbol being used in this particular instance?
& in a type context signifies an intersection type.
https://www.typescriptlang.org/docs/handbook/2/objects.html#intersection-types
This quote is extracted from the provided documentation:
Intersection types are closely related to union types, however, they have distinct purposes. An intersection type combines multiple types into a singular type. This enables you to merge existing types to create a single type encompassing all required functionalities. For instance, Person & Serializable & Loggable represents a type that embodies features of Person, Serializable, and Loggable. Consequently, objects of this type will possess all members from all three individual types.
To illustrate, if your networking requests entail consistent error handling, you could segregate the error handling into its dedicated type and integrate it with types corresponding to distinct response types.
interface ErrorHandling {
success: boolean;
error?: { message: string };
}
interface ArtworksData {
artworks: { title: string }[];
}
interface ArtistsData {
artists: { name: string }[];
}
// These interfaces are amalgamated for uniform error handling and data representation.
type ArtworksResponse = ArtworksData & ErrorHandling;
type ArtistsResponse = ArtistsData & ErrorHandling;
const handleArtistsResponse = (response: ArtistsResponse) => {
if (response.error) {
console.error(response.error.message);
return;
}
console.log(response.artists);
};
Here's an Example to Clarify:
type dog = {age: number, woof: Function};
type cat = {age: number, meow: Function};
// The 'weird' type is an intersection of 'cat' and 'dog'
// It must encompass all attributes from both 'cat' and 'dog'
type weird = dog & cat;
const weirdAnimal: weird = {age: 2, woof: () => {'woof'}, meow: () => {'meow'}}
interface extaprop {
color: string
}
type catDog = weird & extaprop; // This combined type now incorporates the additional property 'color'
const weirdAnimal2: catDog = {age: 2, woof: () => {'woof'}, meow: () => {'meow'}, color: 'red'}
// Note that this differs from a union type
// The type below specifies either a cat OR a dog
type dogOrCat = dog | cat;
To put it simply,
Using the & symbol between two types allows you to access all properties of both types.
On the other hand,
The | symbol means that you can only access properties that are common to both types.
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