JuniorTheoryCommon

What does tsc report for this file?

TypeScript

interface Box { width: number }
interface Box { height: number }
const b: Box = { width: 2 };
console.log(b.width);

An error: the object has no property height

Expecting a duplicate-name error, as with two type aliases: interfaces of one name merge into one type with the members of both.
Expecting the second declaration to replace the first: the members add up, so Box needs both width and height.

What does tsc report if the second declaration also gives width the type string?
Why can two type aliases of one name not merge the same way?

JuniorTheoryCommon

TypeScript

interface Box { width: number }
interface Box { height: number }
const b: Box = { width: 2 };
console.log(b.width);

An error: the object has no property height

Expecting a duplicate-name error, as with two type aliases: interfaces of one name merge into one type with the members of both.
Expecting the second declaration to replace the first: the members add up, so Box needs both width and height.

What does tsc report if the second declaration also gives width the type string?
Why can two type aliases of one name not merge the same way?