TypeScript import stripping

definitions.ts

export type MyType = { foo: string };


export interface MyInterface {
    foo: string;
}

export class MyClass implements MyInterface {
    constructor(private foo: string) { }
}


export enum MyEnum { CASE_1, CASE_2 }

erased.ts

// This import statement will be completely removed from the output JavaScript because none of the imported symbols
// are used for their actual JavaScript value
import { MyType, MyClass, MyInterface, MyEnum } from "./definitions";

const instance: MyInterface = getInstance<MyClass>("my-class");

const theType: MyType = { foo: 'abc' };

class MyOtherClass implements MyInterface {
  
  member: MyEnum;
}

preserved.ts

// This import statement will be transformed to: import { MyClass, MyEnum } from "./definitions";
// because MyClass and MyEnum are actually needed at runtime
import { MyType, MyClass, MyInterface, MyEnum } from "./definitions";

const instance: MyInterface = getInstance(MyClass); // MyClass constructor is actually used here

// types and interfaces are never retained. They do not exist in JavaScript.
const theType: MyType = { foo: 'abc' };

class MyOtherClass implements MyInterface{
  member: MyEnum = MyEnum.CASE_1; // Value of CASE_1 is used here
}