<button onclick="openFile()">Dosya aç</button>
<div id="editor-container" style="display: none">
    <textarea id="editor" cols="50" rows="5"></textarea> <br>
    <button onclick="saveFile()">Kaydet</button>
</div>

<script>
    const editor = document.getElementById('editor'),
        openBtn = document.getElementById('open-file'),
        editorContainer = document.getElementById('editor-container')

    const openFile = async () => {
        [fileHandle] = await window.showOpenFilePicker()
        let file = await fileHandle.getFile()
        editor.value = await file.text()
        editorContainer.style.display = 'block'
    }

    const saveFile = async () => {
        let writable = await fileHandle.createWritable()
        await writable.write(editor.value)
        await writable.close()
    }
</script>