[javascript] Subtract days, months, years from a date in JavaScript

As others have said you're subtracting from the numeric values returned from methods like date.getDate(), you need to reset those values on your date variable. I've created a method below that will do this for you. It creates a date using new Date() which will initialize with the current date, then sets the date, month, and year according to the values passed in. For example, if you want to go back 6 days then pass in -6 like so var newdate = createDate(-6,0,0). If you don't want to set a value pass in a zero (or you could set default values). The method will return the new date for you (tested in Chrome and Firefox).

function createDate(days, months, years) {
        var date = new Date(); 
        date.setDate(date.getDate() + days);
        date.setMonth(date.getMonth() + months);
        date.setFullYear(date.getFullYear() + years);
        return date;    
    }