How in the TypeScript interface to set a common type for any elements of an object?

Question

typescript

interface Obj {
    elemA: MainType;
    elemB: MainType;
}

In addition to elemA, elemB can also be elemC and so on, and they are all of the same type. How to write an interface so that MainType is applied to all elements without requiring them to be written, as in the example?

Answer 1

interface Obj {
    [key: string]: MainType;
    other: OtherType;
}