English?

english.js

let user = { 
  teacherId: 1,
  first: 'Bob', 
  last: 'Smith', 
  room: {
    floor: 2,
    number: 40
  }  
};

// Switchish
if (user.teacherId) {
  // is it a teacher?
  
  // More switchish
  if (user.room) {
    if (user.room.floor === 1) {
      // Do stuff
    } else if (user.room.floor ===2) {
      // Do other stuff
    }
  }
} else if (user.studentId) {
  // is it a student?
} else { ... }

// The point: Once I know that this object is not a student but a teacher, I go on to 
// make more specific checks about the state.  At no point would my initial "narrowing down"
// become invalid where I would want to "fall through" the teacher bits to see if it's a student.