<textarea id="example-id" autocomplete="off"></textarea>

<div>👇現在の文字数</div>
<div id="current-length"></div>
// textarea要素オブジェクト
const textareaElem = document.getElementById("example-id");
// 値を埋め込む先
const currentLengthElem = document.getElementById("current-length");

textareaElem.addEventListener('input', (event) => {
  currentLengthElem.innerText = event.target.value.length;
});

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