# 定義
執行階段才進行型別檢查，相反的在撰寫時就可明確定義變數的型別稱為靜態型別
var num = 1;
console.log(typeof num);//number
var name = 'Tony';
console.log(typeof name);//string
var total = function(){
}
console.log(typeof total);//function
var num = null;
console.log(typeof num);//object
# 顯性轉換(Explicit conversion)
var item = 1;
console.log(typeof item);//number
item = 'phone';
console.log(typeof item);//string
# 隱性轉換(Implicit conversion)
var brand = 1;
console.log(typeof brand);//number
brand = brand + '';
console.log(typeof brand);//string