1 'use strict';
2
3 if (true) {
4     let app = 'apple';
5 }
6
7 console.log(app);　　//外面是访问不到app的

1 'use strict';
2
3 const app = 'apple';
4 console.log(app);
5
6 const app = 'peach';
7 console.log(app);　　//报错，常量不能多次赋值

'use strict';function breakfast () {return ['egg','bread','milk'];
}//传统方法
var arr = breakfast(), egg = arr[0], bread = arr[1], milk = arr[2];
console.log(egg,bread,milk);//es6
let [t1,t2,t3] = breakfast();
console.log(t1,t2,t3);

'use strict';function breakfast () {return {egg:'egg', milk:'milk', bread:'bread'};
}let {egg: a1, milk: a2, bread: a3} = breakfast();    //a1,a2,a3是自己定义的名字
console.log(a1,a2,a3);

'use strict';let food1 = 'egg', food2 = 'bread';let str = `今天的早餐是 ${food1} 和 　　　　　　${food2}`;　　//通过反斜线引号可以对字符串换行console.log(str);

'use strict';let food1 = 'egg', food2 = 'bread';let str = `今天的早餐是 ${food1} 和 ${food2}`;　console.log(str.startsWith('今天'),str.endsWith('bread'),str.includes('早餐'));　　//true true true

1 'use strict';
2
3 function breadfast (food = '食物', drink = '饮料') {
4     console.log(`${food} ${drink}`);
5 }
6
7 breadfast();        //输出默认值
8 breadfast('面包', '啤酒');        //输出给定值

1 'use strict';
2
3 function breakfast (food, drink, ...others) {        //...表示后面除了前面两个参数，其余参数都放在others这个数组里
4     console.log(food, drink, others);
5     console.log(food, drink, ...others);    //将others数组里面的值展开
6 }
7
8 breakfast('面包', '牛奶', '培根', '香肠');

 1 'use strict';
 2
 3 //breakfast是函数名字，箭头前面是传入的参数，箭头后面是返回值
 4 let breakfast = (food,drink) => food + drink;
 5
 6 console.log(breakfast('面包', '牛奶'));
 7
 8 //箭头后面的大括号可以写函数的具体操作
 9 let lunch = (food, drink) => {
10     return '今天午餐吃' + food + '，喝' +drink;
11 };
12
13 console.log(lunch('鸡肉', '汤'));

 1 'use strict';
 2
 3 let food = '鸡肉', drink = '汤';
 4
 5 let breakfast = {
 6     food: food,        //添加属性
 7     drink: drink,
 8     eat(){}            //添加方法
 9 };
10
11 console.log(breakfast);
12
13 //添加属性的其他方法
14 let food1 = 'food1';
15
16 breakfast.afood = '面条';
17 breakfast['hot drink'] = '牛奶';
18 breakfast[food1] = '蔬菜';    //这里的food1是变量food1的值
19
20 console.log(breakfast);

 1 'use strict';
 2
 3 let lunch = {
 4     getDrink(){
 5         return '啤酒';
 6     }
 7 };
 8
 9 let dinner = {
10     getDrink(){
11         return '可乐';
12     }
13 };
14
15 let food1 = Object.create(lunch);
16 console.log(food1.getDrink());                            //啤酒
17 console.log(Object.getPrototypeOf(food1) === lunch);    //true
18
19 Object.setPrototypeOf(food1, dinner);
20 console.log(food1.getDrink());                            //可乐
21 console.log(Object.getPrototypeOf(food1) === dinner);    //true

 1 'use strict';
 2
 3 let lunch = {
 4     getDrink(){
 5         return '啤酒';
 6     }
 7 };
 8
 9 let dinner = {
10     getDrink(){
11         return '可乐';
12     }
13 };
14
15 //__proto__
16 let food2 = {
17     __proto__: lunch        //通过__proto__来指定food2的prototype
18 };
19
20 console.log(food2.getDrink());
21 console.log(Object.getPrototypeOf(food2) === lunch);    //true
22
23 food2.__proto__ = dinner;
24 console.log(food2.getDrink());
25 console.log(Object.getPrototypeOf(food2) === dinner);    //true

 1 'use strict';
 2
 3 let lunch = {
 4     getDrink(){
 5         return '啤酒';
 6     }
 7 };
 8
 9 let dinner = {
10     getDrink(){
11         return '可乐';
12     }
13 };
14
15 //super
16 let food3 = {
17     __proto__: lunch,
18     getDrink(){
19         return super.getDrink() + '和汤';    //super.getDrink()是调用原型的getDrink方法
20     }
21 };
22
23 console.log(food3.getDrink());

 1 'use strict';
 2
 3 function chef(foods){
 4     let i = 0;
 5
 6     return {
 7         next(){
 8             let done = (i >= foods.length);
 9             let value = !done ? foods[i++] : undefined;
10
11             return {
12                 value: value,
13                 done: done
14             }
15         }
16     }
17 }
18
19 let meal = chef(['黄瓜', '鸡蛋']);
20 console.log(meal.next());        //Object {value: "黄瓜", done: false}
21 console.log(meal.next());        //Object {value: "鸡蛋", done: false}
22 console.log(meal.next());        //Object {value: undefined, done: true}

 1 'use strict';
 2
 3 class Chef {
 4     constructor(food){        //创建一个Chef类实例时会自动执行constructor方法
 5         this.food = food;
 6     }
 7
 8     cook(){
 9         console.log(this.food);
10     }
11 }
12
13 let chef1 = new Chef('鸡蛋');
14 chef1.cook();

 1 'use strict';
 2
 3 //Set类似于数组
 4 let food = new Set('鸡蛋');
 5 console.log(food);
 6
 7 food.add('菜');        //添加新的项
 8 food.add('豆');
 9
10 console.log(food);
11
12 console.log(food.size);            //food的长度
13 console.log(food.has('菜'));    //判断是否含有某一项
14 food.delete('豆');                //删除某一项
15 console.log(food);
16
17 food.forEach(food => {            //批量对food中的项进行操作
18     console.log(food);
19 });
20
21 food.clear();                    //清空food
22 console.log(food);