ES6：Symbol创建对象属性及调用方法

1.第一种调用方法：
obj[Reflect.ownKeys(obj)[index]]()

        //向对象中添加方法 up down
        let game = {
            name: 'YY',
            up() {
                console.log('向上');
            },
            down() {
                console.log('向下');
            }
        }

        //声明一个对象
        let methods = {
            up: Symbol(),
            down: Symbol()
        };
        game[methods.up] = function() {
            console.log('up');
        }
        game[methods.down] = function() {
            console.log('down');
        }
        console.log(game);
        game.up(); //向上
        game.down(); //向下

    //调用Symbol创建的函数
    game[Reflect.ownKeys(game)[3]]()  //up
    game[Reflect.ownKeys(game)[4]]()  //down

2.第二种调用方法：
Object.getownPropertySymbols(obj)[index]();

        //直接加入
        let youxi = {
            name: '狼人杀',
            [Symbol('say')]: function() {
                console.log('发言');
            },
            [Symbol('zibao')]() {
                console.log('自爆');
            }
        }
        console.log(youxi);
        console.log(youxi['name']); //狼人杀

    //调用Symbol创建的函数
    const a = Object.getownPropertySymbols(youxi);
    youxi[a[0]](); // 发言
    youxi[a[1]](); // 自爆

3.第三种方法调用：obj[方法名]()

        let up1 = Symbol();
        let down1 = Symbol();
        let game1 = {
            name: 'YY',
            up1() {
                console.log(1);
            },
            down1() {
                console.log(2);
            },
            [up1]() {
                console.log('向上');
            },
            [down1]() {
                console.log('向下');
            }
        }
        console.log(game1);
        game1.up1(); // 1
        game1.down1(); // 2

   //调用Symbol创建的函数
   game1[up1](); // 向上
   game1[down1]();  // 向下