node util 包中帶有is*** 的工具函式，用來進行型別判斷

var util = require("util");
console.log(util.isString("a"))
console.log(util.isArray([]));
console.log(util.isFunction(function(){}));

console.log(util.isNumber(1));
console.log(util.isNumber(1.1));

var b ="1"
console.log(util.isUndefined(b.b));
console.log(util.isUndefined
 
(b));
console.log(util.isDate(new Date()));