Why set prototype's constructor to its constructor function? [duplicate]

Answer 1

It restores the .constructor property that was on the original prototype object that you overwrote. People restore it because it's expected to be there.

Some people like to do...

if (my_obj.constructor === Car) { ... }

This isn't required, since instanceof is a better test IMO.

if (my_obj instanceof Car) { ... }

if (my_obj instanceof Vehicle) { ... }