iframe.html

         <div class="rich_text_area">
             <iframe class="cl" id="editor" name="editor" frameborder="2"  ></iframe>
         </div>
...
    <script src="script.js"></script>
    <script>
        window.onload=()=>{
    
        const editor = document.getElementById('editor');
        const doc = editor.contentDocument;
        console.log(doc);
        console.log(editor);
        doc.designMode = "on";
        editor.contentDocument.designMode = "on";
         
         document.getElementById('boldBtn').addEventListener('click', ()=>{
             doc.execCommand("Bold", false,null);
         })
         document.getElementById('ItalicBtn').addEventListener('click', ()=>{
             doc.execCommand("Italic", false,null);
         })
         document.getElementById('html').addEventListener('click', ()=>{
            //doc.execCommand("Italic", false,null);
             
        })

        };