[js]바닐라자바스크립트로 글자수제한 구현하기

<script>
        var checkUnload = true;
        const countingWords = (category) => {
            if (category == 'one_line') {
                const currentOneline =document.getElementById("one_line").value.length;
                  document.getElementById("current-one-line-num").innerText = currentOneline ;
                 if(currentOneline>40){
                     alert('40자를 넘길 수 없습니다!');
                     const value = document.getElementById("one_line").value;
                     document.getElementById("one_line").value= value.split('',38).join('');
                         document.getElementById("current-one-line-num").innerText = 38 ;
                 }


            } else {
                  const currentOneline =document.getElementById("introduction").value.length;
                  document.getElementById("current-introduction-num").innerText = currentOneline ;
                 if(currentOneline>200) {
                     alert('200자를 넘길 수 없습니다!');
                     const value = document.getElementById("introduction").value;
                     document.getElementById("introduction").value = value.split('', 198).join('');
                     document.getElementById("current-introduction-num").innerText = 198;
                 }
            }
        }

        function onSubmitFunc() {
            checkUnload = false;
        }

        $(window).on("beforeunload", function () {
            if (checkUnload) return "이 페이지를 벗어나면 작성된 내용은 저장되지 않습니다.";
        });
        $('input[type="text"]').keydown(function () {
            if (event.keyCode === 13) {
                event.preventDefault();
            }
            ;
        });


    </script>