Sort by multiple attributes in a backbone collection in the browser

gistfile1.txt

// A multi columns sort implementation that sorts like SQL ORDER BY.

_.extend(Backbone.Collection.prototype, {
 sortOptions: null,
 comparator: function(a, b) {
    var atts = [], dirs = [], att, i;

    if(!this.sortOptions) {
      return 0;
    }

    // take the array of objects {'att':'attName','dir':'dirName'} and put it into two arrays, one for attributes, one for asc/desc
    for(i = 0; i < this.sortOptions.length; i++) {
      atts.push(this.sortOptions[i].att);
      dirs.push(this.sortOptions[i].dir);
    }

    // look through attributes supplied for any that don't have equal values
    att = _.find(atts, function(c) { return a.attributes[c] != b.attributes[c]; });

    // if all the values are equal, att is undefined. No need to sort.
    if(!att) {
      return 0;
    }

    // use that attribute to determine the order. Match the attributes in order to the methods for asc/desc. default = asc
    if((dirs[_.indexOf(atts, att)] || 'asc').toLowerCase() == 'asc') {
       return (a.attributes[att] > b.attributes[att]) ? 1 : -1;
    } else {
       return (a.attributes[att] < b.attributes[att]) ? 1 : -1;
    }
  }
});

// Example usage:
// PeopleList is a collection that is populated.
// Once sorted, render all the models in the collection again to see the sort working

PeopleList.sortOptions = [{'att':'name','dir':'desc'}, {'att':'age','dir':'asc'}];
PeopleList.sort();


// Based on and many thanks to http://www.benknowscode.com/2013/12/multi-column-sort-in-backbone-collections.html