类型

1.Number
2.String
3.Boolean
4.Undefined
5.Null
6.Symbol
7.Object

variables

1. var
2. let
3. const

Conditionals

1. if 2. else 3. esle if 4. ternary operator 5. switch

Logical Operators

1. && 2. || 3. !

Functions

Data Structror

1.Array
2.Object

scope

ES6

EcmaScript 6

let and const

advanced functions

const first = () =>{
  const greet = 'Hi';
  const second = () =>{
     alert(greet)
  }
  return second
}

const newFunc= first();

/* 
*/

advancend arrays

forEach,map,filter,reduce

forEach不改变原数组，对数组内每个元素操作 map遍历数组，需要输出元素，它创建了一个新的数组

filter 过滤器，遍历条件

reduce

const array = [1,2,10,16];

const double =[];
array.forEach(num => double.push(num*2));
console.log(double)
console.log(array)

const mapArray = array.map(num => num*2);
console.log('map',mapArray)

const filterArray = array.filter(num=> num>5);
console.log('filter',filterArray)

const reduceArray = array.reduce((accumulator, sum) => {
    return accumulator +sum;
},11);
console.log('reduce', reduceArray)

/*
foreach (4) [1, 2, 10, 16]
array (4) [2, 4, 20, 32]
map (4) [2, 4, 20, 32]
filter (2) [10, 16]
reduce 40
*/

advanced objects

reference type,context,instantiation

class Player{
    constructor(name,type){
        this.name = name;
        this.type = type;
    }
    introduce(){
        console.log(`Hi I am ${this.name}, I'm a ${this.type}`);
    }
}

class Wizard extends Player{
    constructor(name,type){
        super(name,type);
    }
    play(){
        console.log(`WWWWWWWWeeeeeee I'm a ${this.type}`);
    }
}

const wizard1 = new Wizard('Shelly', "Healer");

/*
wizard1.introduce()
Script snippet #27:7 Hi I am Shelly, I'm a Healer
*/

Es7 Es8

es7 .includes() ```js const array=['bird','cat','dog']

array.includes('bird') //true array.includes('panda') //false

```js
const square = (x) => x**2

square(5)    //25

es8

.padStart() .padEnd()

'Turtle'.padStart(10)   //'    Turtle'
'Turtle'.padEnd(10)   //'Turtle    '

Object.values Object.entries Object.keys

let obj ={
    username0: 'Santa',
    username1: 'Rudolf',
    username2: 'Mr.Crinch'
}

Object.keys(obj).forEach((key,index) => console.log(key,obj[key]))
/*
username0 Santa
username1 Rudolf
username2 Mr.Crinch
*/

Object.values(obj).forEach(value => console.log(value))
/*
Santa
Rudolf
Mr.Crinch
*/

Object.entries(obj).forEach(value => console.log(value))
/*
(2) ['username0', 'Santa']
(2) ['username1', 'Rudolf']
(2) ['username2', 'Mr.Crinch']
*/

Es10

.flat() 展平数组 默认是1级，可更改参数，less than 50

//.flat

const array1 = [1,2,3,4,5];
array1.flat();
//(5) [1, 2, 3, 4, 5]

const array2 = [[1],2,[3,4],5];
array2.flat();
//(5) [1, 2, 3, 4, 5]

const array3 = [[1],2,[3,4],[[5]]];
array3.flat();
//(5) [1, 2, 3, 4, Array(1)]  //[5]

const array4 = [[1],2,[3,4],[[5]]];
array4.flat(2);
//(5) [1, 2, 3, 4, 5]

//清理数组
const entries = ['bob', 'sally',,,,,,'cindy']
entries.flat();
//(3) ['bob', 'sally', 'cindy']

.flatMap()

.trimStart()

.trimEnd()

const userProfiles = [['commanderTom',23],['derekZlander',40],['hansel',18]]

const userObj=Object.fromEntries(userProfiles)
console.log(userObj)
/*
commanderTom: 23
derekZlander: 40
hansel: 18
*/
Object.entries(userObj)

/*
 (2) ['commanderTom', 23]
 (2) ['derekZlander', 40]
 (2) ['hansel', 18]
*/

advanced loop

const basket =['apples','oranges','grapes'];

//1.
for(let i =0;i<basket.length;i++){
    console.log(basket[i]);
}
/*
apples
oranges
grapes
*/
//2.
basket.forEach(item => {
    console.log(item)
})
/*
apples
oranges
grapes
*/
//3. for of
//Iterating - arrays,strings
for(item of basket){
    console.log(item)
}
/*
apples
oranges
grapes
*/

const detailedBasket = {
    apples: 5,
    oranges: 10,
    grapes: 1000
}

//4. for in  - properties
//enumerating - objects
for(item in detailedBasket){
    console.log(item)
}

ES2020

BigInt
Nullish Codescing Operator ??
Optional Chaining Operator ?.

let will_pokemon = {
    pikachu: {
        species: 'Mouse pokemon',
        height: 0.4,
        weight: 6
    }
}

let andri_pokemon = {
    raichu:{
        species: 'Mouse pokemon',
        height: 0.8,
        weight: 30
    }
}

let weight = will_pokemon.pikachu.weight;
console.log('weight',weight)
//weight 6

let weight2 =''
if(andri_pokemon.pikachu&&andri_pokemon.pikachu.weight)
 weight2 = andri_pokemon.pikachu.weight;
else 
    weight2= undefined;
console.log('weight2',weight2)
//weight2 undefined

//es2020
let weight3 = andri_pokemon?.pikachu?.weight;
console.log('weight3',weight3)
//weight3 undefined

globalThis

globalThis

Debugging

const flattened = [[0,1],[2,3],[4,5]].reduce((a,b) => a.concat(b),[]);
//console.log(flattened)
//(6) [0, 1, 2, 3, 4, 5]

//console.log()
const flattened1 = [[0,1],[2,3],[4,5]].reduce((a,b) =>{
    console.log('b',b);
    console.log('a',a);
    return a.concat(b)
} ,[]);

//debugger
const flattened2 = [[0,1],[2,3],[4,5]].reduce((a,b) =>{
    debugger
    return a.concat(b)
} ,[]);

Modules

IIFE