JavaScript: Date.AddMonth

Date.prototype.AddMonth = function(val){
    val = parseInt(val);
    var m = this.getMonth();
    m += val;
    if (m > 11) {
        while (m > 11) {
            m -= 12;
            this.setYear(this.getFullYear() + 1);
        }
    } 
    if (m < 0) {
        while (m < 0) {
            m += 12;
            this.setYear(this.getFullYear() - 1);
        }
    } 
	this.setMonth(m);
}

Date.prototype.AddMonth = function(val){ val = parseInt(val); var m = this.getMonth(); m += val; if (m > 11) { while (m > 11) { m -= 12; this.setYear(this.getFullYear() + 1); } } if (m < 0) { while (m < 0) { m += 12; this.setYear(this.getFullYear() - 1); } } this.setMonth(m); }