JSFiddle - React, Tailwind, and code Playground

JavaScript

// var actualDate = new Date('2014-12-16'); //this works
 var actualDate = new Date('2014-12-31'); // does not increment month

        var year = actualDate.getFullYear();
        var monthy = actualDate.getMonth()+1;
        var days = actualDate.getDate()+3;
        var out = year + '-' + (monthy < 10 ? '0' : '') + monthy + '-' + days;

console.log(out);