getTypes.js

getTypes = function (field) {
     var alltypes=[
                { t: "Regex", minv: Timestamp(2147483647,9999) },
                { t: "Timestamp", minv: Timestamp(0,0) },
                { t: "ISODate", minv: new Date(0,0,0) },
                { t: "True", minv: true },
                { t: "False", minv: false },
                { t: "ObjectId", minv: ObjectId("000000000000000000000000") },
                { t: "BinData", minv: BinData(0,"") },
                { t: "Array", minv: [] },
                { t: "Subdocument", minv: {} },
                { t: "String", minv: "" },
                { t: "Number", minv: NumberLong("-9223372036854775807") },
                { t: "Null", minv: null }
     ] ;

     var maxPos=alltypes.length;

     var con=[];
     con[maxPos]="Other/Unknown";
     for (pos = maxPos-1; pos > -1; pos--) {
        con[pos] = {"$cond":{
              if: {$gte:[field, alltypes[pos]["minv"] ]},
              then:  alltypes[pos]["t"],
              else:  con[pos+1]
        }};
     }
     return con[0];
}