JavaScript date function allow to input time difference from now.

myDateFunction.js

function myDate(description) {
    var result = new Date();
    if (description === undefined || description == "" || description.trim() == "") {
        console.info(description + "=[" + result + "]");
        return result;
    }
    var desc = description.trim().toLowerCase();
    var section = desc.split(" ");
    if (section.length < 2) {
        console.info(description + "=[" + result + "]");
        return result;
    }
    var temp = 0;
    for (var i = 0; i < section.length; i++) {
        var word = section[i];
        if (!isNaN(word)) {
            temp = parseInt(word);
        } else {
            if (section[section.length - 1] == "ago") {
                temp *= -1;
            }
            switch (word) {
                case 'second':
                case 'seconds':
                    result.setSeconds(result.getSeconds() + temp);
                    break;
                case 'minute':
                case 'minutes':
                    result.setMinutes(result.getMinutes() + temp);
                    break;
                case 'hour':
                case 'hours':
                    result.setHours(result.getHours() + temp);
                    break;
                case 'day':
                case 'days':
                    result.setDate(result.getDate() + temp);
                    break;
                case 'month':
                case 'months':
                    result.setMonth(result.getMonth() + temp);
                    break;
                case 'year':
                case 'years':
                    result.setFullYear(result.getFullYear() + temp);
                    break;
                default:
                    break;
            }
            temp = 0;
        }
    }
    console.info(description + "=[" + result + "]");
    return result;
}

var time = myDate();
time = myDate("2 years 13 month ago");
time = myDate("1 years 1 month ago");
time = myDate("1 years 1 month 1 day 1 hour 1 minute 1 second ago");

time = myDate("in 2 years 13 month");
time = myDate("in 1 years 1 month");
time = myDate("in 1 years 1 month 1 day 1 hour 1 minute 1 second");