let form = document.getElementById("form");
let info = document.getElementById("res");
let typeInput = document.getElementById("type");

form.onsubmit = async (e) => {
    e.preventDefault();
  
    if(form.num1.value === "") return;
    if(form.num2.value === "") return;
  
    let index = form.selected.selectedIndex;
    let op = form.selected.options[index].textContent;
    let res = "";
  
    function chooseOperation(oper){
      switch(oper){
        case "Сложение":
          return "sum"
        case "Вычитание":
          return "minus"
        case "Переворачивание":
          return "reverse"
        case "Сравнение":
          return "comparison"
      }
    }
    let type = typeInput.value;
    let operstor = chooseOperation(op)
    if(form.num2.value == 0)
        return;
    res = await fetch(`http://localhost:8080/${operstor}?first=${form.num1.value}&second=${form.num2.value }&type=${type}`)

    res = await res.text();

    form.res.value = res;
  }