multiple sorting in backbone.js -

sorting in backbone it's working fine. want sort multiple fields, passing sort argument dynamically clicking sorting headers. have 5 headers(id,desc,type,category,hierarchy). when click headers it's sort ascending , next click descending problem sort 1 attribute want multiple attribute pass collection , maintain previous sorting order , again sort till data relative.

in collection:

   sortasc: function(sortfield) {        var key = sortfield;         this.comparator = function(model) {             return model.get(key);         };           this.sort();     },      sortdesc: function(sortfield) {         var key = sortfield;         this.comparator = function(a, b) {             = a.get(key);             b = b.get(key);             return < b ?  1 : > b ? -1 : 0;         }         this.sort();     }, 

view: called when click header(click event) , elem id (dynamically change on click) id,,desc,category,type , hierarchy.

        sortitems: function(e) {                     if ( currentclass.indexof("ascending")>0 ) {             this.currentcollection.sortasc(elem.id);         }          else {             this.currentcollection.sortdesc(elem.id);         }      }, 

i create function receives comparators array , return composite comparator comparators[n] tie breaker of comparator[n-1]

var createcompositecomparators = function(comparators){   return function(a,b){      var = 0;      var tempresult = 0;      for(i=0; i<comparators.length; i++){         tempresult = comparators[i](a,b);         if (tempresult !== 0 ) return tempresult;      }      return tempresult;   }; }; 

and function creates comparator field, should accept [+|-]fieldname (e.g. +count or -count)

var createfieldcomparator = function(fullfield){   var field = fullfield.substring(1);   var desc = fullfield.substring(0,1) === "-" ? -1 : 1;   return function(a, b) {         return  desc * (a.get(field) - b.get(field));     }; } 

to finalize sortbyfields:

sortbyfields: function(sortfields){ // array   var comparators = _.map(sortfields, createfieldcomparator);//create list of comparators list of fields in form of [+|-]field   this.comparator = createcompositecomparators(comparators);   this.sort(); } 

to use send array of fields

collection.sortbyfields(["+category", "-id"]); 

off course code not production ready... not tested