定義常量

const T = '我是一個常量，常量是一旦定義不能修改的';

console.log(T)//我是一個常量，常量是一旦定義不能修改的

標籤模板 ``
 

let divId = 'div';

let divText = 'div 文字'

let html = `<div id=${divId}>${divText}</div>`

變數會被直接解析 

console.log(html)
<div id=div>div 文字</div>

${ }可以解析變數 函式 常量 

in includes 用於 判斷物件,陣列 字元 是否存在某個屬性，元素，字元

let a = {c:'ccc',d:'ddd','e':false} 
'c' in a
15:00:04.226 true
'e' in a
15:00:25.282 true

'cc' in a
15:02:53.974 false

let a = [1,2,3];
a.includes(1)
14:32:32.291 true
14:32:44.911 let b = '12345';
14:32:44.912 undefined
14:32:55.942 b.includes(3)
14:32:55.946 true

for of 迴圈 

用於迴圈 陣列  set 型別 

let forssa= ['c','b','ccc','bbb']; for(let w of forssa){console.log(w)}
 c
 b
 ccc
 bbb
let set = new Set();
set.add('aaaaa')
 for(let seta of set){console.log(seta)}
 aaaaa

let map = new Map();

map.set('d','dddddddddddddc');

map.set('c','ccccccc');

for(let mapa of map){console.log(mapa)}

["c", "ccccccc"]

["d", "dddddddddddddc"]

set map es6新資料型別

set 

可用方法

add  / has / size / keys / values ／delete ／clear ／entries

map

 set ／get ／ has ／ delete ／ clear 

共同特點，不允許有重複的值