Time-like string format.js

/*
Description:
Build up a method that takes an integer and formats it to a 'time - like' format.

The method must raise an exception if its hour length is less than 3 digits and greater than 4.

Example:
solution(800); // should return '8:00'
solution(1000); // should return '10:00'
solution(1451); // should return '14:51'
solution(3351); // should return '33:51'
solution(10000); // should raise an exception
*/
function solution(hour) {
  let str=hour.toString()
  if (str.length>4||str.length<3) throw Error()
  if (str.length===4) return str[0]+str[1]+':'+str[2]+str[3]
  else return  str[0]+':'+str[1]+str[2]
}