一文详解如何在项目中和平时练习中应用es6语法

const obj = {
    a:1,
    b:2,
    c:3,
    d:4,
    e:5,
}
 
const a = obj.a;
const b = obj.b;
const c = obj.c;
const d = obj.d;
const e = obj.e;

const {a,b,c,d,e} = obj;

const {a:a1} = obj;
console.log(a1)

const a = [1,2,3];
const b = [1,5,6];
const c = a.concat(b);//[1,2,3,1,5,6]
 
const obj1 = {
  a:1,
}
const obj2 = {
  b:1,
}
const obj = Object.assign({}, obj1, obj2);//{a:1,b:1}

const a = [1,2,3];
const b = [1,5,6];
const c = [...new Set([...a,...b])];//[1,2,3,5,6]
 
const obj1 = {
  a:1,
}
const obj2 = {
  b:1,
}
const obj = {...obj1,...obj2};//{a:1,b:1}

const name = '小明';
const score = 59;
let result = '';
if(score > 60){
  result = `${name}的考试成绩及格`; 
}else{
  result = `${name}的考试成绩不及格`; 
}

const name = '小明';
const score = 59;
const result = `${name}${score > 60?'的考试成绩及格':'的考试成绩不及格'}`;

if(
    type == 1 ||
    type == 2 ||
    type == 3 ||
    type == 4 ||
){
   //...
}

const condition = [1,2,3,4];
 
if( condition.includes(type) ){
   //...
}

const a = [1,2,3,4,5];
const result = a.filter( 
  item =>{
    return item === 3
  }
)

const a = [1,2,3,4,5];
const result = a.find( 
  item =>{
    return item === 3
  }
)

const name = obj && obj.name;

const name = obj?.name;

if(value !== null && value !== undefined && value !== ''){
    //...
}

if((value??'') !== ''){
  //...
}

const a = 0 ?? '默认值a';
cosnt b = null ?? '默认值b';
 
console.log(a); // "0"  0是假值，但不是 null 或者 undefined
console.log(b); // "默认值b"

const a = 0；
const b = a || 5
 
 
//当0作为有效值，与我们期望的 b 的值不一致
console.log(b); // 5

const fn1 = () =>{
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve(1);
    }, 300);
  });
}
const fn2 = () =>{
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve(2);
    }, 600);
  });
}
const fn = () =>{
   fn1().then(res1 =>{
      console.log(res1);// 1
      fn2().then(res2 =>{
        console.log(res2)
      })
   })
}

const fn = async () =>{
  const res1 = await fn1();
  const res2 = await fn2();
  console.log(res1);// 1
  console.log(res2);// 2
}

function fn (name, age) {
  let name = name || 'hsq'
  let age = age || 22
  console.log(name, age)
}
fn() // hsq 22

function fn (name = 'hsq', age = 22) {
  console.log(name, age)
}
fn() // hsq 22
fn('test', 23) // test 23

function fn (name, ...params) {
  console.log(name)
  console.log(params)
}
fn ('hsq', 1, 2) // hsq [ 1, 2 ]
fn ('hsq', 1, 2, 3, 4, 5) // hsq [ 1, 2, 3, 4, 5 ]

function fn () {}
 
const fn = function () {}

const fn = () => {}
 
// 如果只有一个参数，可以省略括号
const fn = name => {}
 
// 如果函数体里只有一句return
const fn = name => {
    return 2 * name
}
// 可简写为
const fn = name => 2 * name
 
// 如果返回的是对象
const fn = name => ({ name: name })
 

const obj = {
  name: 'hsq',
  age: 22,
  gender: '男'
}
 
const values = Object.keys(obj)
console.log(values) // [ 'hsq', 22, '男' ]

const obj = {
  name: 'hsq',
  age: 22,
  gender: '男'
}
 
const values = Object.values(obj)
console.log(values) // [ 'hsq', 22, '男' ]

const obj = {
  name: 'hsq',
  age: 22,
  gender: '男'
}
 
const entries = Object.entries(obj)
console.log(entries) 
// [ [ 'name', 'hsq' ], [ 'age', 22 ], [ 'gender', '男' ] ]

const arr = [1, 2, 3, [4, 5, 6]]
 
console.log(arr.flat()) // [ 1, 2, 3, 4, 5, 6 ]

const arr = [1, 2, 3, [4, 5, 6, [7, 8, 9]]]
 
console.log(arr.flat(2))
[
  1, 2, 3, 4, 5,
  6, 7, 8, 9
]

const arr = [1, 2, 3, [4, 5, 6, [7, 8, 9, [10, 11, 12]]]]
 
console.log(arr.flat(Infinity))
[
   1,  2, 3, 4,  5,
   6,  7, 8, 9, 10,
   11, 12
]