ES6（ECMAScript2015） 基础知识 浅析

1.块级作用域（let）

{

let fruit = “apple”;

}

console.log(fruit)

会报错，因为{ }大括号包含的区域为块级作用域，let在其中申明的变量只能在该块中生效

2.恒量声明（const）

const fruit = "apple";

fruit = "banana";

console.log(fruit)

会报错，因为const声明的是恒量，不能被重新赋值，只能用方法改变，如const arr = [ ]，可以使用arr.push()

3.结构写法

数组写法：

function breakfast() {

return ["cake", "tea", "apple"];

}

let [dessert, drink, fruit] = breakfast();

console.log(dessert, drink, fruit) ------ cake tea apple

对象写法：

function breakfast() {

return { dessert: "cake" , drink: "tea" , fruit: "apple"};

}

let {dessert: drink , drink: dessert , fruit: fruit} = breakfast();

console.log(dessert, drink, fruit) ------ tea cake apple

4. …用法

当做展开的用法：

let fruits = ['apple', 'banana'],

foods = ['cake', ...fruits];

console.log(fruits) ------ ["apple", "banana"]

console.log(...fruits) ------ apple banana

console.log(foods) ------- ["cake", "apple", "banana"]

函数参数数组包容：

function breakfast(dessert, drink, ...foods) {

console.log(dessert, drink, foods) ------ cake tea ["apple", "pear"]

}

breakfast("cake", "tea", "apple", "pear")

5.字符模板

 let dessert="cake",drink="tea";

let breakfast=`今天早餐是${dessert}和${drink}!`;  使用反引号包裹

console.log(breakfast) ------ 今天早餐是cake和tea!

查看字符串以什么开头：

console.log(breakfast.startsWith(‘今天’)) ------ true

查看字符串以什么结尾：

console.log(breakfast.endsWith(‘今天’)) ------ false

查看字符串以是否包含什么：

console.log(breakfast.includes(‘今天’)) ------ true

标签字符串：kitchen是设置的任意标签名

var dessert = "cake",drink = "tea";

var breakfast = kitchen `今天早餐是${dessert}和${drink}!`;

function kitchen(string, ...values) {

console.log(string); ------ ["今天早餐是", "和", "!", raw: Array[3]]

console.log(values); ------ ["cake", "tea"]

}

6.函数设置

设置函数参数的默认值：

function breakfast(drink = "tea", fruit = "apple") {

return `${drink} ${fruit}`;

}

console.log(breakfast()) ------ tea apple

console.log(breakfast("coffee", "banana")) ------ coffee banana

结构对象：

function breakfast(dessert, drink, {location,name}={}) { 设置默认值防止报错

console.log(dessert, drink, location,name) ------ cake tea 兰州 董小姐

}

breakfast("cake", "tea", {location:"兰州",name:"董小姐"})

name属性：

let func=function breakfast() { }

console.log(func.name) ------ breakfast

Arrow Functions 箭头函数：

let breakfast = (dessert, drink) => {

console.log(dessert + drink) ------ caketea

return dessert

}

console.log(breakfast('cake', 'tea')) ------ cake

let lunch = (dessert, drink) => dessert

console.log(lunch('cake', 'tea')) ------- cake

创建对象属性中的函数

let dessert = 'cake' , drink = 'tea';

let food = {

dessert,

drink,

 breakfast() { }  类似于breakfast: function() { }

}

console.log(food) ------ Object {breakfast: () , dessert: "cake" , drink: "tea"}

console.log(food.breakfast) ------ breakfast() {}

迭代next()：

function* chef(foods) {  function后面加上*号

for (var i = 0; i < foods.length; i++) {

yield foods[i];

}

}

let dinner = chef(["egg" , "apple"])

console.log(dinner.next()) ------ Object {value: "egg", done: false}

console.log(dinner.next()) ------ Object {value: "apple", done: false}

console.log(dinner.next()) ------ Object {value: undefined, done: true}

7.对象设置

设置具有空格的属性名：

let food={};

// food.hot drink="tea";   直接设置会报错

food['hot drink']="tea";

console.log(food) ------ Object {hot drink: "tea"}

判断相等：

console.log(+0 === -0) ------ true

console.log(Object.is(+0, -0)) ------ false

console.log(NaN === NaN) ------ false

console.log(Object.is(NaN, NaN)) ------ true

属性赋值：

let breakfast = {}

Object.assign(

breakfast,

{drink: 'beer'},

{fruit: 'apple'},

{fruit: 'pear'}  此处会替换上面设置的apple

)

console.log(breakfast) ------ Object {drink: "beer", fruit: "pear"}

判断设置对象的prototype：

let breakfast = {

getDrink() { return "beer" }

}

let lunch = {

getDrink() { return "tea" }

}

let sunday = Object.create(breakfast);

console.log(sunday.getDrink()); ------ beer

console.log(Object.getPrototypeOf(sunday) === breakfast) ------ true

Object.setPrototypeOf(Sunday , lunch);

console.log(sunday.getDrink()); ------ tea

console.log(Object.getPrototypeOf(sunday) === lunch) ------ true

设置对象的__proro__：

let breakfast = {

getDrink() { return "beer" }

}

let lunch = {

getDrink() { return "tea" }

}

let sunday = { __proto__:breakfast }

console.log(sunday.getDrink()); ------ beer

console.log(Object.getPrototypeOf(sunday) === breakfast) ------ true

sunday.__proto__=lunch;

console.log(sunday.getDrink()); ------ tea

console.log(Object.getPrototypeOf(sunday) === lunch) ------ true

sunday = {

__proto__: breakfast,

getDrink() {

return super.getDrink() + "tea";  super可以执行之前设置的方法

}

}

console.log(sunday.getDrink()); ------ beertea

8.类class

创建一个类：

class chef {

constructor(food) {

this.food = food;

this.dish = [];

}

set menu(dish) {

this.dish.push(dish);

}

get menu() {

return this.dish

}

cook() {

console.log(this.food); ------ apple

}

static cook2(food) {  设置静态的方法

console.log(food) ; ------ orange

}

}

let dinner = new chef("apple")

dinner.cook();

console.log(dinner.menu = "banana"); ------ banana

console.log(dinner.menu = "pear"); ------ pear

console.log(dinner.menu); ------ [‘banana’ , ‘pear’]

chef.cook2("orange") 调用静态方法

类的继承：

    class Person {

constructor(name, birthday) {

this.name = name;

this.birthday = birthday;

}

intro() {

return `${this.name},${this.birthday}`;

}

}

 class Chef extends Person {  Chef通过extends继承Person的内容

constructor(name, birthday) {

super(name, birthday);   执行Person中的内容

}

}

let dinner = new Chef('Tom', '1992-03-07');

console.log(dinner.intro()); ------ Tom,1992-03-07

9.创建一个Map

let food = new Map();

let fruit = {} , cook = function() {} , dessert = 'cake';

food.set(fruit, 'apple');

food.set(cook, 'fork');

food.set(dessert, 'cake');

console.log(food); ------ Map {Object {} => "apple", function => "fork", "cake" => "cake"}

console.log(food.size); ------ 3

console.log(food.get(fruit)); ------ apple

food.delete(dessert);

console.log(food.has(dessert)); ------ false

food.forEach((value, key) => {

console.log(`${key}=${value}`);

})

------ [object Object]=apple

------ function () {}=fork

food.clear();

10.模块导入需要使用辅助工具，查阅相关文档