Meteor - update var on select change

Question

I've got a dropdown, but when a user select another value, I want some code to be executed. My question: How can I check whether the selected value of the dropdown has changed?

In my html file:

<template name="jaren">    
    <form id="yearFilter">
        <select class="selectpicker span2" id="yearpicker" >
            {{#each jaren}}
                {{#if selectedYear}}
                <option selected value="{{_id}}">{{jaar}} {{description}}</option>
                {{else}}
                <option value="{{_id}}">{{jaar}} {{description}}</option>
                {{/if}}
            {{/each}}
        </select> 
    </form>
</template>

in my javascript file:

Template.jaren.jaren = function() {
  return Years.find();
}
Template.jaren.selectedYear = function() {
  if (Session.get('year_id') == this._id) {
    return true;
  } else {
    return false;
  }
}
Template.jaren.events({
  'change form#yearFilter #yearpicker': function(event, template) {
    Session.set('year_id', template.find('#yearpicker').value);
    console.log("value changed");
  }
});

Answer 1

You can get the value of the select element inside the event handler and then compare it to the old value you had already stored:

"change #yearpicker": function(evt) {
  var newValue = $(evt.target).val();
  var oldValue = Session.get("year_id");
  if (newValue != oldValue) {
    // value changed, let's do something
  }
  Session.set("year_id", newValue);
}

Answer 2

A solution with pure JavaScript would be:

'change #yearpicker': function (event) {
  var currentTarget = event.currentTarget;
  var newValue = currentTarget.options[currentTarget.selectedIndex].value;
  if(!Session.equals('year_id', newValue)){
    Session.set('year_id', newValue);
  }
}