Why do constructor functions return objects, but not primitives in JavaScript? [duplicate]

Answer 1

That's because, by definition, the purpose of constructors is producing objects, not primitives:

4.3.4 constructor

function object that creates and initialises objects

Therefore, the [[Construct]] internal method (called via the new operator), checks the type of the value returned by [[Call]]:

13.2.2 [[Construct]]

8. Let result be the result of calling the [[Call]] internal property of F, providing obj as the this value and providing the argument list passed into [[Construct]] as args.
9. If Type(result) is Object then return result.
10. Return obj.

In fact, this is an invariant:

[[Construct]] ( )

• The Type of the return value must be Object.