typeof 1 // number
typeof '1' // string
typeof true // boolean
typeof Symbol('1') // symbol
typeof undefined // undefined

typeof function(){} // function
typeof { a: 1 } // object
typeof [1, 2, 3] // object 這里會(huì)判斷異常，建議使用Array.isArray區(qū)分?jǐn)?shù)組和對(duì)象

//以下也會(huì)判斷異常
typeof new Boolean(true) === 'object';
typeof new Number(1) === 'object';
typeof new String('abc') === 'object';

//最后來(lái)看null
typeof null // object

語(yǔ)法：object instanceof constructor 
object 某個(gè)實(shí)例對(duì)象 constructor 某個(gè)構(gòu)造函數(shù)

'abc' instanceof String //false 檢查原型鏈會(huì)返回undefined
new String('abc') instanceof String //true
new Boolean(true) instanceof Boolean // true 
new Number(1) instanceof Number // true

順便做一下簡(jiǎn)單實(shí)現(xiàn)
function new_instance_of(leftVaule, rightVaule) { 
		let leftProto = leftVaule.__proto__; // 取左表達(dá)式的__proto__值
  let rightPrototype = rightVaule.prototype; // 取右表達(dá)式的 prototype 值
  
  while (true) {
  	if (leftProto === null) {
      return false;	
    }
    if (rightPrototype === rightProto) {
      return true;	
    } 
    leftProto = leftProto.__proto__ 
  }
}

''.constructor == String  //true 
new Number(1).constructor == Number  //true 
new Function().constructor == Function //true 
true.constructor == Boolean  //true
new Date().constructor == Date //true

var toString = Object.prototype.toString;

toString.call(new Date); // [object Date]
toString.call(new String); // [object String]
toString.call(Math); // [object Math]

toString.call(undefined); // [object Undefined]
toString.call(null); // [object Null]

//lodash.baseGetTag部分重要源碼

//如果值是undefined和null返回對(duì)應(yīng)tag
   if (value == null) {
    return value === undefined ? 
 				'[object Undefined]' 
 				: 
 				'[object Null]'
   }
   // 如果不支持Symbol或者value值上面沒(méi)有Symbol.toStringTag屬性，
		 //直接返回Object.prototype.toString調(diào)用后的值  
   if (!(symToStringTag && symToStringTag in Object(value))) {
    return toString.call(value)
   }