需要优化if语句

Question

I make a currency converter and as a result it turns out that the condition operators are almost identical, it would be better to somehow optimize through the ternary operator

 var exchan=document.getElementById("exchan"); exchan.addEventListener("click",function(e){ var numberOne=document.getElementById("numberOne").value; var numberTwo=document.getElementById("numberTwo"); var sExchange; var currencyOne=document.getElementById("currencyOne").value; var currencyTwo=document.getElementById("currencyTwo").value; if(currencyOne=="UAH" && currencyTwo=="USD"){ numberTwo.value=(numberOne/cursUSD).toFixed(2); } if(currencyOne=="UAH" && currencyTwo=="EUR"){ numberTwo.value=(numberOne/cursEUR).toFixed(2); } if(currencyOne=="UAH" && currencyTwo=="PLN"){ numberTwo.value=(numberOne/cursPLN).toFixed(2); } },false);

Answer 1

Instead of standalone variables cursUSD , cursEUR , etc, onsider using an object indexed by the currency abbreviation. Then, just look up the conversion factor on the object:

const conversions = {
  USD: <value of cursUSD>,
  EUR: <value of cursEUR>,
  PLN: <value of cursPLN>
};
const exchan = document.getElementById("exchan");
exchan.addEventListener("click", function(e) {
  const [numberOneVal, currencyOneVal, currencyTwoVal] = ['numberOne', 'currencyOne', 'currencyTwo']
    .map(id => document.getElementById(id).value);
  if (currencyOneVal === "UAH" && conversions[currencyTwoVal]) {
    document.getElementById("numberTwo").value = (numberOneVal / conversions[currencyTwoVal]).toFixed(2);
  }
}, false);

Answer 2

You can make the check for 'currencyOne' on the top part, since all your check require it, and it will evaluate once. You can create a variable to hold the value of the operation, since the onlything changing is the value of the currencyTwo, so that you only have one line of 'numberTwo.value' assignment. You could use a switch if the if/else does not suite you for the inner checkings

 var curOperator;
    if(currencyOne=="UAH")
    {
     if(currencyTwo=="USD") curOperator = cursUSD; 
     else if(currencyTwo=="EUR") curOperator = cursEUR;  
     else if(currencyTwo=="PLN") curOperator = cursPLN; 
     else
        throw;
    }

    numberTwo.value=(numberOne/curOperator).toFixed(2);