# 類 > 類(class)本質上是 es5 構造函數的另一種寫法. </br> > </br> > **注意:** </br> > 1.class 定義的對象，不用 **new 關鍵字**聲明是無法運行的，和函數加 () 是有些區別的. > 2.class 不存在變量提升. > 3.class 內部使用的是嚴格模式. ```javascript //es5 var Monkey = function(name, age) { this.name = name; this.age = age; this.lol = function() { console.log("i'm laughing~"); }; }; var monkey1 = new Monkey('neer', 2); monkey1.lol(); console.log("i'm" + monkey1.name + ', ' + monkey1.age + 'years old'); //es6 class Monkey { constructor(name, age) { this.name = name; this.age = age; } lol() { console.log("i'm laughing~"); } } let monkey1 = new Monkey('neer', 2); monkey1.lol(); console.log(`i'm ${monkey1.name}, ${monkey1.age} years old`); //子類必須在constructor方法中調用super方法，否則新建實例時會報錯。這是因為子類沒有自己的this對象，而是繼承父類的this對象，然后對其進行加工。如果不調用super方法，子類就得不到this對象。 // 類的繼承 class Person { constructor(name, gender) { this.name = name; this.gender = gender; } introduction() { console.log(`my name is ${this.name} and i'm a ${this.gender}`); } } class Son extends Person { constructor(name, gender, age) { super(name, gender); this.age = age; } call() { console.log( `i'm ${this.name}'s son, my father is ${this.gender},i was ${ this.age } years old ` ); } } ```