functionInaFunction.js

function higher (d) ({
  add3: () => (d + 3)
})

const higher = (d) => ({
  add3: () => d + 3
})

class higher {
  constructor (d) {
    this.d = d
  }
  add3 () {
    return this.d + 3
  }
}

const c = new higher(3)

// console.log(typeof(higher))

console.log(c.add3())
  

Two way to declare a class(function)

1. Declare a function
2. Declare a class without a constructor
3. Declare a class with a constructor