x.valueOf()
x.valueOf.call(undefined)
TypeError: Object.prototype.valueOf: 'this' is null or undefined
x.valueOf.call(null)
TypeError: Object.prototype.valueOf: 'this' is null or undefined
x.valueOf.call()
TypeError: Object.prototype.valueOf: 'this' is null or undefined
typeof x.valueOf.call(true)
object
typeof x.valueOf.call(42)
object
typeof x.valueOf.call('Hello')
object