字符串
通过单引号，双引号，反引号都是字符串
外双内单
let str = 'abc'
let str1 = "abc"
let str2 = `abc`
console.log("你说'你好'啊")字符串中间用 ${ } 包含变量
let age = 18
document.write("我今年${age}岁了")外双内单
let str = 'abc'
let str1 = "abc"
let str2 = `abc`
console.log("你说'你好'啊")let age = 18
document.write("我今年${age}岁了")