simple two way binding with vanilla js as explained by Blaize Stewart (@theonemule) at https://www.wintellect.com/data-binding-pure-javascript/

Binding.js

// inspired by @theonemule (Blaize Stewart) via https://www.wintellect.com/data-binding-pure-javascript/

window.Binding = (function () {
	var bindingStore = {};

	function Binding(prop, obj) {
		if (!obj) {
			obj = bindingStore;
			bindingStore[prop] = undefined;
		}

		var self = this;

		this.bindings = [];

		this.value = obj[prop];
		this.valueGetter = function () {
			return self.value;
		};
		this.valueSetter = function (val) {
			for (var i = 0; i < self.bindings.length; i++) {
				var binding = self.bindings[i];

				if (binding.func) {
					if (binding.scope) {
						val = binding.func.apply(binding.scope, [val]);
					} else {
						val = binding.func(val);
					}
				}

				if (binding.element && binding.attribute) {
					binding.element[binding.attribute] = val;
				}

				if (binding.element && binding.style) {
					binding.element.style[binding.style] = val + 'px';
				}
			}
			self.value = val;
		};

		this.addElement = function (element, attribute, event) {
			var binding = {
				element: element,
				attribute: attribute
			};

			if (event) {
				element.addEventListener(event, function (event) {
					self.valueSetter(element[attribute]);
				})
				binding.event = event;
			}

			this.bindings.push(binding);
			element[attribute] = self.value;

			return self;
		};

		this.addFunction = function (func, scope) {
			var binding = {
				func: func,
				scope: scope
			};

			this.bindings.push(binding);

			if (scope) {
				func.apply(scope, [self.value]);
			} else {
				func(self.value);
			}

			return self;
		};

		this.addStyle = function (element, style) {
			var binding = {
				element: element,
				style: style
			};

			this.bindings.push(binding);
			element.style[style] = self.value + 'px';

			return self;
		}

		Object.defineProperty(obj, prop, {
			get: this.valueGetter,
			set: this.valueSetter
		}); 

		obj[prop] = this.value;
	}

	Binding.store = bindingStore;

	return Binding;
})();

I use https://raw.githack.com/ to embed this gist with proper mimetype into my codepen.io pens as https://gist.githack.com/matths/1ea82b24326692d327b7c265a9dee8fa/raw/5c88c31d0ec3e73941164a2dfa51d47a6df58822/Binding.js