In TypeScript, a class can be defined as shown below:
class Sup {
static member: any;
static log() {
console.log('sup');
}
}
If you write the following code:
let x = Sup;
Why does the type of x show up as typeof Sup (highlighted in vscode) and what does typeof Sup mean? Is it related to the typeof operator?
Moreover, how would you type something like let y = Object.create(Sup)?
Is it correctly typed as
let y: typeof Sup = Object.create(Sup)typeof in TypeScript has a unique definition compared to regular JavaScript. It serves as an operator for determining the type of an entity within the value space.
let person = { name: 'bob', age: 26 }
type Person = typeof person // Person is { name: string, age: number }
// These declarations are all the same
let personRef1: { name: string, age: number } = person
let personRef2: typeof person = person
let personRef3: Person = person
let personRef4 = person
// additional examples
let secret = 'helloworld'
type Secret = typeof secret // string
let key = 123
type Key = typeof key // number
let add = (a: number, b: number) => a + b
type Add = typeof add // (a: number, b: number) => number
When assigning SomeClass to a variable, the variable's type becomes typeof SomeClass. The format remains unchanged, unlike other examples, due to the ambiguity involved in simplifying class types; it stays as typeof SomeClass for clarity.
When encountering the statement let x = Sup; in your scenario, it essentially means that variable x is capable of storing the constructor function Sup, rather than an actual instance of it:
class Sup { }
let x: typeof Sup;
x = Sup; // acceptable
x = new Sup(); // not valid
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