pascal and camel case - js advanced

function solve() {
  const text = document.getElementById("text").value;
  const naming = document.getElementById("naming-convention").value;
  const resultContainer = document.getElementById("result");

  const splitted = text.split(" ");

  const resultString = "";
  if (naming == "Pascal Case") {
      for (let i = 0; i < splitted.length; i++) {
        resultString += splitted[i][0].toUpperCase() +
        splitted[i].slice(1, splitted[i].length).toLowerCase();
      }
  } else if (naming == "Camel Case") {
    resultString += splitted[0][0].toLowerCase()
    + splitted[0].slice(1, splitted[0].length).toLowerCase();
    for (let i = 1; i < splitted.length; i++) {
      resultString += splitted[i][0].toUpperCase() +
      splitted[i].slice(1, splitted[i].length).toLowerCase();
    }
  } else {
    resultContainer.textContent() = resultString;
  }
  resultContainer.textContent = "Error";
}