Cannot get selected value of Select2 dropdownlist

Question

I use Select2 Dropdown dropdownlist in my MVC project as shown below. Although I can pass the "query" parameter via AJAX by setting it directly, I cannot get the selected text or value of dropdownlist in the data section below. How to get it?

@Html.DropDownListFor(x => x.StudentId, Enumerable.Empty<SelectListItem>(), 
    new { style ="width: 100%;" } )

$("#StudentId").select2({
   multiple: false,
   placeholder: "Select",
   allowClear: true,
   tags: true,

   ajax: {
       url: '/Grade/StudentLookup',
       dataType: 'json',
       delay: 250,

       data: function (params) {
           return {
               //q: params.Name, // search term
               //page: params.page
               query : 'test' //this parameter can be passed via AJAX
               //!!! but I cannot get the selected text or value of dropdownlist 
           };
       },              

       processResults: function (data, page) {
           var newData = [];
           $.each(data, function (index, item) {
               newData.push({
                   id: item.Id,     //id part present in data 
                   text: item.Name  //string to be displayed
               });
           });
           return { results: newData };
       },
       cache: true
   },
   escapeMarkup: function (markup) { return markup; }, // let our custom formatter work
   minimumInputLength: 0, //for listing all, set : 0
   maximumInputLength: 20, // only allow terms up to 20 characters long
});

Answer 1

You can simply listen to the select2:select event to get the selected item.

Events

select2:select

Triggered whenever a result is selected.

 var select2 = $(".select2"); select2.select2({ multiple: false, placeholder: "Select", allowClear: true, tags: true, width: "180" }); function onSelect(evt) { console.log($(this).val()); } select2.on('select2:select', onSelect) 

 @import url('https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.3/css/select2.min.css'); 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.3/js/select2.min.js"></script> <select class="select2"> <option value="item-1">Item 1</option> <option value="item-2">Item 2</option> <option value="item-3">Item 3</option> <option value="item-4">Item 4</option> <option value="item-5">Item 5</option> <option value="item-6">Item 6</option> <option value="item-7">Item 7</option> <option value="item-8">Item 8</option> <option value="item-9">Item 9</option> <option value="item-10">Item 10</option> </select> 

Answer 2

============================== SOLVED ==============================

Here is the solution of the problem:

In order to send the text value in Select2 via AJAX use params.term in the data section as shown below. Many thanks to @DavidDomain as his answer also very useful in order to use selected index change.

//code omitted for brevity
data: function (params) {
   return {
             query: params.term, // search term
             page: params.page
           };
   }, 
...