Edit in JSFiddle

Date.prototype.AddDays = function(noOfDays) {
    this.setTime(this.getTime() + (noOfDays * (1000 * 60 * 60 * 24)));
    return this;
}
    
$(function() {
    $("a").click(function() {
        var dateNew = new Date();
        var noOfDays = $("#input").val();
        
        dateNew.AddDays(noOfDays);
        $("#result").val(dateNew);
        return false;
    });
});

<input type='text' id="input" value="1"/>
<a id="add-days" href="#">Add Days</a>

<input type='text' id="result"/>