データ型の判断
var str = 'abc'
var num = 123
var boo = true
var arr = [1, 2, 3]
var obj = {
}
var fun = function() {
}
var nul = null
var und;
console.log(Object.prototype.toString.call(str))
console.log(Object.prototype.toString.call(num))
console.log(Object.prototype.toString.call(boo))
console.log(Object.prototype.toString.call(arr))
console.log(Object.prototype.toString.call(obj))
console.log(Object.prototype.toString.call(fun))
console.log(Object.prototype.toString.call(nul))
console.log(Object.prototype.toString.call(und))