function convert(currency) { var inputValue = Number(document.querySelector('input[type=number]').value); var result; if (currency === 'dolar') { result = (inputValue / 32).toFixed(2) + ' Dolar = '+inputValue + ' TL'; } else if (currency === 'euro') { result = (inputValue / 40).toFixed(2) + ' Euro = '+inputValue + ' TL'; } else if (currency === 'sterlin') { result = (inputValue / 45).toFixed(2) + ' Pound = '+inputValue + ' TL'; } document.getElementById("resultTextbox").value = result; }