JSFiddle - React, Tailwind, and code Playground

HTML

<script src="//cdn.ckeditor.com/4.5.7/standard/ckeditor.js"></script>
<textarea id="container">How are you!</textarea>

JavaScript

CKEDITOR.replace('container', {
    on: {
        instanceReady: function( evt ) {
		        console.log('instanceReady', evt)
            
            evt.editor.addCommand("mySimpleCommand", {
                exec: function(edt) {
                    alert(edt.getData());
                }
            });
            evt.editor.ui.addButton('SuperButton', {
                label: "Click me",
                command: 'mySimpleCommand',
                toolbar: 'insert',
                icon: 'https://avatars1.githubusercontent.com/u/5500999?v=2&s=16'
            });
        }
    }
});