let str = "1.txt"
// let arr = Array.from(str).reverse()
// console.log(arr)
// let i = arr.findIndex(v=>v==".")
// let arr1 = arr.slice(0,i).join("");
// console.log(arr1)
let i = str.lastIndexOf(".")
console.log(i)
let c = str.slice(i)
console.log(c)