ES6~(ES2015)
1.新类型
symbol
2.声明变量
-
let 块级作用域，不存在变量提升（需先声明，后使用），且作用域“锁死”(在域里面不能先用在声明)
-
const块级作用域，var函数作用域
var tem = '1' function k2() { tem = 'kkk'; console.log(tem) // kkk var tem } k2() function k1() { tem = 'kkk'; // Cannot access 'tem' before initialization console.log(tem) let tem // var tem } k1()
3.解构赋值
-
字符串
① const [a,b,c,d,e] = 'hello'; //b =》e ② let {length: len} = 'hello' //len =》5 -
数组
① var [a, b, c] = [1, 2, 3] ② let [foo, [[bar,], baz]] = [1, [[2], 3]] ③ let [head, ...tail] = [1, 2, 3, 4] //...tail =》 2,3,4; ...rest运算符; 类 对象扩展运算符 --arguments: let a = [1,2,3]; let b = [...a]; ④ let [a,b='kk'] = ['33'] // b 的默认值是'kk' -
对象
var foo; ({foo} = {foo:'bbb'}) ① var {foo, bar} = {bar:'bbb', foo:'aaa'} ② let {foo:baz} = {foo:'aaa', bar:'bbb'}// baz =》'aaa' foo =》undefined (var {foo:foo, bar:bar} = {foo:'aaa', bar:'bbb'}) ③ 重命名变量名： let 后端数据 = {a:1, b:2} let {a:name, b:sex} = 后端数据; console.log(name) =》 1 -
函数
function add([x, y]){ return x+y; } add([1,2])
4.字符串
-
模板字符串(
${})let a ='你好'; let b = `hello ${a} world 世界。`; // hello 你好 world 世界 -
增(后两es2017)
repeat() padStart() padEnd() -
查
includes() startsWith() endsWith()
{}
codePointAt()
fromCodePoint()
5.正则
-
修饰符
u、y
-
stickey属性
是否有y修饰符
-
flangs属性
返回修饰符
6.数组
json => array:
Array.form(json); // 类数组转成真正数组， 如new set([1,1,12,3,45])
数字、文本、变量 Array.of(1,2,3);
-
find()
let arr=[1,2,3,4,5,6,7,8,9]; console.log(arr.find(function(value,index,arr){ return value > 5; })) -
fill()
let arr=[0,1,2,3,4,5,6,7,8,9];
arr.fill('jspang',2,5); //填充内容 start end
console.log(arr);
for (let item of arr )
for (let item of arr.keys() )
for (let [ index, val ] of arr.entries() )
```
let arr=['jspang','技术胖','大胖逼逼叨']
let list=arr.entries();
console.log(list.next().value);
console.log(list.next().value);
console.log(list.next().value);
```
- in（对象和数组是否存在）
```
obj = { a: 'blogs'}
console.log('a' in obj); // true
arr = [ 'blogs', '博客园']
console.log(0 in arr); // true
```
- forEach、filter、some、map(替换)、
- toString();
- arr.map(function (arrItem) { /**/ }) 循环数组
### <h1 id="h7"> 7.函数 </h1>
- 参数默认值： y = y|r --> (y=4)
- name
- 箭头函数
```
var a = 0;
let obj1 = {
a: 1,
fn1: function () {
setTimeout(function () {
console.log('普通函数')
console.log(this.a) // 指向调用的对象
},1000)
}
}
let obj2 = {
a: 2,
fn2: function () {
setTimeout( () => {
console.log('箭头函数')
console.log(this.a) // 指向所处的对象
},1000)
}
}
obj1.fn1()
obj2.fn2()
```
### <h1 id="h8"> 对象 </h1>
-
```
var name = 'name', function = 'function'; var obj = {name,function}
```
- 结构
```
var foo = ‘bar’
var baz = {foo}
=> es5
var baz = {foo:'baz'}
```
- function结构
```
var o = {
method () {}
}
=> es5
var o = {
method:function(){}
}
```
- 对象的属性
```
obj['a' + 'bc'] = 123;
=> es5
let obj = {
[prokey] : true,
['a' + 'bc'] : 123;
};
```
- name
```
返回对象名称 Object.is(NaN,NaN); Object.is(+0,-0);
```
- assign
```
合并
```
- for...of
- 模块
```
{ cid as c, aid as a, family as f}
export default vs export import
```
### <h1 id="h9"> 数据结构 </h1>
**new Map()** :map为解决对象中的键值不能为非数字,map((当前元素值,小标,当前数组)=>{})
**new Set()**
```
var m = new Map()
m.set('Adam', 67)
```
### <h1 id="h10"> 历史 </h1>
- ES8(ES2017) [new **`Uint8Array()`**](https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array)
- **babal**
```
npm install -g babel-cli (全局)
npm install --save-dev babel-preset-es2015 babel-cli（生产环境）
```
- promize
https://www.jianshu.com/p/7e60fc1be1b2
- ??
```
1.?? 的意思是，如果 ?? 左边的值是 null 或者 undefined，那么就返回右边的值。
let a = 99;,b=null;
console.log(b??a) => 99 =>
```
- bug1
```
bug1:Invalid attempt to destructure non-iterable instance
let [name,id] = {name: 'tony', id: 1}; // 左右两边类型不同
```
- 生成器函数
>（步骤生成器） function* -- yield -- next().value
> yield 有return效果，但next()就走下一个next
```
function* step(i) {
yield i;
console.log('下一步')
yield i*3;
}
let k = step(10)
console.log(k.next().value) // 10
console.log(k.next().value) // 下一步 30
```
### <h1 id="ck"> 参考 </h1>
[ES6文档](https://es6.ruanyifeng.com/#docs/promise)
https://www.cnblogs.com/lgyong/p/8711550.html
[E6 ~ E10](https://www.cnblogs.com/miaSlady/p/10955729.html)
.lgyong
