前端面试题 驼峰转下划线，下划线转驼峰

let str = "helloWorldHello"
let str2 = "hello_orld_ello"
let result = str.replace(/[A-Z]/g,(p, m) => {
    return '_'+p.toLowerCase()
})
let result1 = str2.replace(/_[a-z]/g,(p,m)=>{
    return p[1].toUpperCase()
})