Select2 dropdown but allow new values by user?

Just for the sake of keep the code alive, I'm posting @rrauenza Fiddle's code from his comment.

HTML

<input type='hidden' id='tags' style='width:300px'/>

jQuery

$("#tags").select2({
    createSearchChoice:function(term, data) { 
        if ($(data).filter(function() { 
            return this.text.localeCompare(term)===0; 
        }).length===0) 
        {return {id:term, text:term};} 
    },
    multiple: false,
    data: [{id: 0, text: 'story'},{id: 1, text: 'bug'},{id: 2, text: 'task'}]
});

For version 4+ check this answer below by Kevin Brown

In Select2 3.5.2 and below, you can use something like:

$(selector).select2({
  minimumInputLength:1,
  "ajax": {
    data:function (term, page) {
      return { term:term, page:page };
    },
    dataType:"json",
    quietMillis:100,
    results: function (data, page) {
      return {results: data.results};
    },
    "url": url
  },
  id: function(object) {
    return object.text;
  },
  //Allow manually entered text in drop down.
  createSearchChoice:function(term, data) {
    if ( $(data).filter( function() {
      return this.text.localeCompare(term)===0;
    }).length===0) {
      return {id:term, text:term};
    }
  },
});

(taken from an answer on the select2 mailing list, but cannot find the link now)

The excellent answer provided by @fmpwizard works for Select2 3.5.2 and below, but it will not work in 4.0.0.

Since very early on (but perhaps not as early as this question), Select2 has supported "tagging": where users can add in their own value if you allow them to. This can be enabled through the tags option, and you can play around with an example in the documentation.

$("select").select2({
  tags: true
});

By default, this will create an option that has the same text as the search term that they have entered. You can modify the object that is used if you are looking to mark it in a special way, or create the object remotely once it is selected.

$("select").select2({
  tags: true,
  createTag: function (params) {
    return {
      id: params.term,
      text: params.term,
      newOption: true
    }
  }
});

In addition to serving as an easy to spot flag on the object passed in through the select2:select event, the extra property also allows you to render the option slightly differently in the result. So if you wanted to visually signal the fact that it is a new option by putting "(new)" next to it, you could do something like this.

$("select").select2({
  tags: true,
  createTag: function (params) {
    return {
      id: params.term,
      text: params.term,
      newOption: true
    }
  },
  templateResult: function (data) {
    var $result = $("<span></span>");

    $result.text(data.text);

    if (data.newOption) {
      $result.append(" <em>(new)</em>");
    }

    return $result;
  }
});

Since many of these answers don't work in 4.0+, if you are using ajax, you could have the server add the new value as an option. So it would work like this:

1. User searches for value (which makes ajax request to server)
2. If value found great, return the option. If not just have the server append that option like this: [{"text":" my NEW option)","id":"0"}]
3. When the form is submitted just check to see if that option is in the db and if not create it before saving.