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();
