JSFiddle - React, Tailwind, and code Playground

JavaScript

var dates = {
   convert:function(d) {
      // Converts the date in d to a date-object.
      return (
        d.constructor === Date ? d :
        d.constructor === Array ? new Date(d[0],d[1],d[2]) :
        d.constructor === Number ? new Date(d) :
        d.constructor === String ? new Date(d) :
        typeof d === "object" ? new Date(d.year,d.month,d.date) :
        NaN
      );
    },
    inRange:function(d,start,end) {
       // Checks if date in d is between dates in start and end.
       return (
        isFinite(d=this.convert(d).valueOf()) &&
        isFinite(start=this.convert(start).valueOf()) &&
        isFinite(end=this.convert(end).valueOf()) ?
        start <= d && d <= end :
        NaN
       );
    }
}

var d = new Date('October 13, 2014 11:13:00');
var start = new Date('October 12, 2014 11:13:00');

console.log (dates.inRange(d, start, d));