Rich text editor as a form input (WYSIWYG contenteditable)

div-as-input.js

(function(){
        // This is a WYSIWYG editing div that can be used as in input in a form.
        // Usage: <div contenteditable is="with-input" name="..."></div>
        // This can be used in a form and values will be submitted as with a text input.
        // You can also get the input with:
        // Array.from(document.querySelectorAll('input')).reduce((d,e) => {d[e.name]=e.value;return d;}, {});
        // The div is a visual component.  An invisible input is appended to
        // hold the form data.  Any changes made to the div will change the
        // value of the input element.
        const global = window;
        var MutationObserver = global.MutationObserver || global.WebKitMutationObserver || global.MozMutationObserver;
        try {
        var proto = Object.create(HTMLDivElement.prototype);
        proto.createdCallback = function() {
                var self = this;
                // The input element:
                var input = this.input = document.createElement('input');
                input.setAttribute('type','text');
                input.setAttribute('name',this.getAttribute('name'));
                input.setAttribute('value',this.innerHTML);
                input.style.display = 'none';
                this.insertAdjacentElement('afterend', input);
                // Update the input element on edit:
                var observer = this.observer = new MutationObserver((mutations) => input.value = this.innerHTML);
                observer.observe(this, { childList: true, characterData: true, subtree: true });
                // Want changes in the input to be refelected in the div but this part doesn't work yet:
                input.addEventListener("change", () => this.innerHTML = input.value);
        };
        var nCB = document.registerElement("with-input", {
                prototype: proto,
                extends: 'div'
        });
        } catch(e){console.error(e.message)}
})();

Demo: https://jsfiddle.net/bitdivine/35rz76tb/2/