js 导入excel时间显示5位数解决方法

时间显示为5位数比如2019/12/31会显示为43830，其实这个43830就是1900-01-01到2019/12/31的天数，取1900-01-01跟Unix时间戳起始时间1970-01-01的天数来换算的，我们只要把它转化为时间戳，然后再由时间戳转化为日期格式就ok了，下边上代码

function formatDate(numb) {

            var second = 25569,
                    day_timestamp = 24 * 60 * 60 * 1000;
            //把五位数的numb转化为时间戳类型，单位是毫秒
            var cTime = (numb - second) * day_timestamp;
                 //如果numb为空或者不为时间类型，则原数据赋值
            if (cTime.toString() == 'NaN'|| cTime <= 0){
                return numb
            }else {
                //转化为时间格式
                return timestamptodate('Y-m-d',cTime)
            };

        }
        function timestamptodate(format, timestamp){
            var a, jsdate=((timestamp) ? new Date(timestamp) : new Date());
            var pad = function(n, c){
                if((n = n + "").length < c){
                    return new Array(++c - n.length).join("0") + n;
                } else {
                    return n;
                }
            };
            var txt_weekdays = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];
            var txt_ordin = {1:"st", 2:"nd", 3:"rd", 21:"st", 22:"nd", 23:"rd", 31:"st"};
            var txt_months = ["", "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"];
            var f = {
                // Day
                d: function(){return pad(f.j(), 2)},
                D: function(){return f.l().substr(0,3)},
                j: function(){return jsdate.getDate()},
                l: function(){return txt_weekdays[f.w()]},
                N: function(){return f.w() + 1},
                S: function(){return txt_ordin[f.j()] ? txt_ordin[f.j()] : 'th'},
                w: function(){return jsdate.getDay()},
                z: function(){return (jsdate - new Date(jsdate.getFullYear() + "/1/1")) / 864e5 >> 0},

                // Week
                W: function(){
                    var a = f.z(), b = 364 + f.L() - a;
                    var nd2, nd = (new Date(jsdate.getFullYear() + "/1/1").getDay() || 7) - 1;
                    if(b <= 2 && ((jsdate.getDay() || 7) - 1) <= 2 - b){
                        return 1;
                    } else{
                        if(a <= 2 && nd >= 4 && a >= (6 - nd)){
                            nd2 = new Date(jsdate.getFullYear() - 1 + "/12/31");
                            return date("W", Math.round(nd2.getTime()/1000));
                        } else{
                            return (1 + (nd <= 3 ? ((a + nd) / 7) : (a - (7 - nd)) / 7) >> 0);
                        }
                    }
                },

                // Month
                F: function(){return txt_months[f.n()]},
                m: function(){return pad(f.n(), 2)},
                M: function(){return f.F().substr(0,3)},
                n: function(){return jsdate.getMonth() + 1},
                t: function(){
                    var n;
                    if( (n = jsdate.getMonth() + 1) == 2 ){
                        return 28 + f.L();
                    } else{
                        if( n & 1 && n < 8 || !(n & 1) && n > 7 ){
                            return 31;
                        } else{
                            return 30;
                        }
                    }
                },

                // Year
                L: function(){var y = f.Y();return (!(y & 3) && (y % 1e2 || !(y % 4e2))) ? 1 : 0},
                //o not supported yet
                Y: function(){return jsdate.getFullYear()},
                y: function(){return (jsdate.getFullYear() + "").slice(2)},

                // Time
                a: function(){return jsdate.getHours() > 11 ? "pm" : "am"},
                A: function(){return f.a().toUpperCase()},
                B: function(){
                    // peter paul koch:
                    var off = (jsdate.getTimezoneOffset() + 60)*60;
                    var theSeconds = (jsdate.getHours() * 3600) + (jsdate.getMinutes() * 60) + jsdate.getSeconds() + off;
                    var beat = Math.floor(theSeconds/86.4);
                    if (beat > 1000) beat -= 1000;
                    if (beat < 0) beat += 1000;
                    if ((String(beat)).length == 1) beat = "00"+beat;
                    if ((String(beat)).length == 2) beat = "0"+beat;
                    return beat;
                },
                g: function(){return jsdate.getHours() % 12 || 12},
                G: function(){return jsdate.getHours()},
                h: function(){return pad(f.g(), 2)},
                H: function(){return pad(jsdate.getHours(), 2)},
                i: function(){return pad(jsdate.getMinutes(), 2)},
                s: function(){return pad(jsdate.getSeconds(), 2)},
                //u not supported yet

                // Timezone
                //e not supported yet
                //I not supported yet
                O: function(){
                    var t = pad(Math.abs(jsdate.getTimezoneOffset()/60*100), 4);
                    if (jsdate.getTimezoneOffset() > 0) t = "-" + t; else t = "+" + t;
                    return t;
                },
                P: function(){var O = f.O();return (O.substr(0, 3) + ":" + O.substr(3, 2))},
                //T not supported yet
                //Z not supported yet

                // Full Date/Time
                c: function(){return f.Y() + "-" + f.m() + "-" + f.d() + "T" + f.h() + ":" + f.i() + ":" + f.s() + f.P()},
                //r not supported yet
                U: function(){return Math.round(jsdate.getTime()/1000)}
            };

            return format.replace(/[\ ]?([a-zA-Z])/g, function(t, s){
                if( t!=s ){
                    // escaped
                    ret = s;
                } else if( f[s] ){
                    // a date function exists
                    ret = f[s]();
                } else{
                    // nothing special
                    ret = s;
                }
                return ret;
            });
        }