gistfile1.js

var SelectThing = Backbone.View.extend({
  
  events: {
    'input .select1': 'updateFirstSelect',
    'input .select2': 'updateSecondSelect'
  },
  
  template: _.template($('#select-thing-template').html()),
  
  initialize: function(collection1, collection2) {
    this.firstSelectValue = "";
    this.secondSelectValue = "";
    
    this.firstSelectItems = collection1;
    this.secondSelectItems = collection2;
  },
  
  updateFirstSelect: function(e) {
    var value = $(e.currentTarget).val();
    if (this.secondSelectValue == "whatever") {
      // do some logic
    }
    this.firstSelectValue = value;
  },
  
  updateSecondSelect: function(e) {
    var value = $(e.currentTarget).val();
    if (this.firstSelectValue == "whatever") {
      // do some logic
    }
    this.secondSelectValue = value;
  }
  
  render: function() {
    this.$el.html(this.template({
      firstSelectItems: this.firstSelectItems,
      secondSelectItems: this.secondSelectItems
    }));

    return this;
  }
})