JSFiddle - React, Tailwind, and code Playground

JavaScript

// this is very similar to using Object.watch()
// instead we attach multiple listeners
var myModel = (function () {
    var actualValue,
        interceptors = [];

    function callInterceptors(newValue) {
        for (var i = 0; i < interceptors.length; i += 1) {
            interceptors[i](newValue);
        }
    }

    return {
        get value() {
            // user never has access to the private variable "actualValue"
            // we can control what they get back from saying "myModel.value"
            return actualValue;
        },

        set value(newValue) {
            callInterceptors(newValue);
            actualValue = newValue;
        },

        listen : function (fn) {
            if (typeof fn === 'function') {
                interceptors.push(fn);
            }
        }
    };
}());

// add a listener
myModel.listen(function (passedValue) {
    alert('You tried to set myValue to ' + passedValue);
});

// add another listener
myModel.listen(function (passedValue) {
    alert('AAARRG! Why did you modify that value to ' + passedValue + '?!?!');
});

// our functions are called when we
// modify our value
myModel.vale = 0;