"The undefined is not an object, so there is no toString."How do you understand this sentence?Is it that only Object can toString and none of the other six data types can toString?Which data types can be toString?
let y = 1
console.log(y.toString()) // 1
y = [1,"1a"]
console.log(y.toString()) // 1,1a
y = {data:1}
console.log(y.toString()) // [object Object]