ES6與ES5對照—–’類’

// ES5

function Application() {
    this.a = 123;
    this.b = 456;

    this.foo = function() {
        return 135;
    }
}

var pro = Application.prototype;

pro.bar = function() {
    return 246;
}

var app = new Application();

console.dir(typeof Application);    // => 'function'
console.dir(Application);           // => [Function: Application]
console.dir(app);                   // => {a:123, b: 456, foo: [function]}
console.dir(typeof app);            // => 'object'
console.dir(app.bar());             // => 246

// ES6

class Application {

    // constructor方法默許返回實例對象，1個類必須有該方法，沒有會被默許添加
    constructor() {              
        this.a = 123;           // => this指代新的實例對象，即new的對象
        this.b = 456;
        this.foo = function() {
            return 135;
        }
    }

    bar() {
        return 246;
    }
}

let app = new Application();

console.dir(typeof Application);    // => 'function'
console.dir(Application);           // => [Function: Application]
console.dir(app);                   // => {a:123, b: 456, foo: [function]}
console.dir(typeof app);            // => 'object'
console.dir(app.bar());             // => 246

console.dir(app.constructor);       // => [Function: Application]

* 可以發現，兩次的打印1模1樣，我們可以理解為class實際上是構造函數的1個語法糖，只是為了讓JavaScript看起來更像1門面向對象的語言 *