x.valueOf()
x.valueOf.call(undefined)
TypeError: undefined is not an object (evaluating 'x.valueOf.call(undefined)')
x.valueOf.call(null)
TypeError: null is not an object (evaluating 'x.valueOf.call(null)')
x.valueOf.call()
TypeError: undefined is not an object (evaluating 'x.valueOf.call()')
typeof x.valueOf.call(true)
object
typeof x.valueOf.call(42)
object
typeof x.valueOf.call('Hello')
object