encodeDecodeMsg

function encodeAndDecodeMessages() {
    let firstBtn = document.querySelectorAll("#main div button")[0];
    let secondBtn = document.querySelectorAll("#main div button")[1];

    let inputEl = document.querySelectorAll("#main div textarea")[0];
    let outputEl = document.querySelectorAll("#main div textarea")[1];

    firstBtn.addEventListener("click", encode);
    secondBtn.addEventListener("click", decode);

    let resultString = "";

    function encode(event) {
        resultString = "";
        let inputValue = inputEl.value;
        outputEl.value = "";

        for (let i = 0; i < inputValue.length; i++) {
            let newSymbol = String.fromCharCode(inputValue.charCodeAt(i) + 1);

            resultString += newSymbol;
        }
        inputEl.value = "";
        outputEl.value = resultString;
    }

    function decode(event) {
        let decoded = "";
        for (let i = 0; i < resultString.length; i++) {
            let newSymbol = String.fromCharCode(resultString.charCodeAt(i) - 1);
            decoded += newSymbol;
        }
        outputEl.value = decoded;
    }
}