Take a look at this TypeScript code snippet:
lib.ts
interface Person {
name: string;
age: number;
}
export default class PersonFactory {
getPerson(): Person {
return {
name: "Alice",
age: 30,
}
}
}
index.ts
import PersonFactory from "./lib";
export class Bar {
person: any;
constructor() {
const factory = new PersonFactory();
this.person = factory.getPerson();
}
calculateAgeDifferenceWithError(age: number): number {
return age - this.person.name;
}
calculateAgeDifferenceWithTypingAndAutocomplete(age: number): number {
const factory = new PersonFactory();
return age - factory.getPerson().name;
}
}
The issue lies in the "person" property of the "Bar" class. It's difficult to define the type of this variable as the "Person" interface from lib.ts.
In the "calculateAgeDifferenceWithError" method, there is a mistake - using a number "age" and a string "name" in an arithmetic operation, but neither the IDE nor the TypeScript compiler detect it because, in this context, the type of "this.person.name" is set to "any".
In the "calculateAgeDifferenceWithTypingAndAutocomplete" method, I simply use the "getPerson" method. The IDE and compiler recognize the type of the method result which is the "Person" interface with a "string" field for "name". This method triggers an error during compilation.
I encountered this problem when attempting to import a .d.ts file of a JavaScript library where exporting the required interface was not possible. Is there a way to define the valid type of the "person" property without repeatedly copying and pasting the "Person" interface whenever setting the type (and without inline type declarations, like { name: string, age: number })?
I do not intend to create instances of non-exported classes; I just need type checking and auto-completion features.
P.S. I attempted to use this:
person: Person
and received a compiler error: "error TS2304: Cannot find name 'Person'" (as expected)
P.S.S I also tried using the triple-slash directive:
///<reference path="./lib.ts" />
but unfortunately, that didn't work either.
Apologies for my limited English proficiency and thank you for your responses