<input class="weui-input" id="date" type="date" onchange="fn()" value="" placeholder="取款日期填写今日往后三天的时间">
      
   function fn(){
        var dateB = document.getElementById('date').value;
        var date=new Date(dateB);
        var  newDate   =   DateAdd( "d ",3,date);  
        // 转换中国标准时间
        var PZQ = format(newDate,'yyyy-MM-dd');
        // 改变值
        $("#date").val(PZQ);
    }

    function format(time, format){
    var t = new Date(time);
    var tf = function(i){return (i < 10 ? '0' : '') + i};
    return format.replace(/yyyy|MM|dd|HH|mm|ss/g, function(a){
        switch(a){
            case 'yyyy':
                return tf(t.getFullYear());
                break;
            case 'MM':
                return tf(t.getMonth() + 1);
                break;
            case 'mm':
                return tf(t.getMinutes());
                break;
            case 'dd':
                return tf(t.getDate());
                break;
            case 'HH':
                return tf(t.getHours());
                break;
            case 'ss':
                return tf(t.getSeconds());
                break;
        }
    })
}

function   DateAdd(interval,number,date)  
{  
/* 
  *   功能:实现VBScript的DateAdd功能. 
  *   参数:interval,字符串表达式，表示要添加的时间间隔. 
  *   参数:number,数值表达式，表示要添加的时间间隔的个数. 
  *   参数:date,时间对象. 
  *   返回:新的时间对象. 
  *   var   now   =   new   Date(); 
  *   var   newDate   =   DateAdd( "d ",5,now); 
  *---------------   DateAdd(interval,number,date)   ----------------- 
  */  
        switch(interval)  
        {  
                case   "y "   :   {  
                        date.setFullYear(date.getFullYear()+number);  
                        return   date;  
                        break;  
                }  
                case   "q "   :   {  
                        date.setMonth(date.getMonth()+number*3);  
                        return   date;  
                        break;  
                }  
                case   "m "   :   {  
                        date.setMonth(date.getMonth()+number);  
                        return   date;  
                        break;  
                }  
                case   "w "   :   {  
                        date.setDate(date.getDate()+number*7);  
                        return   date;  
                        break;  
                }  
                case   "d "   :   {  
                        date.setDate(date.getDate()+number);  
                        return   date;  
                        break;  
                }  
                case   "h "   :   {  
                        date.setHours(date.getHours()+number);  
                        return   date;  
                        break;  
                }  
                case   "m "   :   {  
                        date.setMinutes(date.getMinutes()+number);  
                        return   date;  
                        break;  
                }  
                case   "s "   :   {  
                        date.setSeconds(date.getSeconds()+number);  
                        return   date;  
                        break;  
                }  
                default   :   {  
                        date.setDate(d.getDate()+number);  
                        return   date;  
                        break;  
                }  
        }  
}