ddd329

function isValid(s) {
  return /^\d+(\.\d{1,2})?$/.test(s);
}

console.log(isValid('123')) //true
console.log(isValid('123.')) //false
console.log(isValid('12.3')) //true
console.log(isValid('1.23')) //true
console.log(isValid('0.123')) //false