textarea with syntax highlighting

        function inputHandler(event) {
            let code, inp;
            // Clone text into pre immediately
            // code = event.target.previousElementSibling.firstChild;
            // if (!code) return;
            inp = document.querySelector('#stack-input');
            code = inp.previousElementSibling.firstChild;
            code.textContent = inp.value;

            // Highlight the syntax
            Prism.highlightElement(code); // , Prism.languages.javascript, 'javascript');
        }
        document.getElementById('stack-input').addEventListener('input', inputHandler);
        document.getElementById('stack-input').addEventListener('focus', inputHandler);
        window.addEventListener('load', inputHandler);