select2/docs/announcements-4.0.html

---
layout: default
title: Select2 4.0.0 Released
slug: announcements-4.0
---

<div class="container">
  <section id="pre-release">
    <h1>Pre-release notes</h1>

    <hr />

    <p class="lead">
      The 4.0 release is ready for early adopters interested in testing it out.
      You can use the development version, available on GitHub, by getting the
      source code available in the <code>select2-ng</code> branch. The source
      code can be
      <a href="https://github.com/select2/select2/archive/select2-ng.zip">
        downloaded as a <code>zip</code> archive
      </a> as well.
    </p>
  </section>

  <hr />

  <section id="release">
    <h1>Select2 4.0.0</h1>

    <p>
      The 4.0 release of Select2 is the result of three years of working on the
      code base and watching where it needs to go. At the core, it is a full
      rewrite that addresses many of the extensibility and usability problems
      that could not be addressed in previous versions.
    </p>

    <p>
      This release contains many breaking changes, but easy-upgrade pathes have
      been created as well as helper modules that will allow for backwards
      compatibility to be maintained with past versions of Select2. Upgrading
      <em>will</em> require you to read the release notes carefully, but the
      migration path should be relatively straightforward. You can view a list
      of the most common changes that you will need to make
      <a href="https://github.com/select2/select2/releases">in the release notes</a>.
    </p>

    <p>
      Below is an in-depth review of what is new in Select2, as well as some of
      the major changes that have been made.
    </p>
  </section>

  <section id="new">
    <h2>New features</h2>

    <p>
      The notable features of this new release include:
    </p>

    <ul>
      <li>
        A more flexible plugin framework that allows you to override Select2 to
        behave exactly how you want it to.
      </li>
      <li>
        Consistency with standard <code>&lt;select&gt;</code> elements for all
        data adapters, removing the need for hidden <code>&lt;input&gt;</code>
        elements.
      </li>
      <li>
        A new build system that uses AMD to keep everything organized.
      </li>
      <li>
        Less specific selectors allowing for Select2 to be styled to fit the
        rest of your application.
      </li>
    </ul>
  </section>

  <section id="plugins">
    <h2>Plugin system</h2>

    <p>
      Select2 now provides interfaces that allow for it to be easily extended,
      allowing for anyone to create a plugin that changes the way Select2 works.
      This is the result of Select2 being broken into four distinct sections,
      each of which can be extended and used together to create your unique
      Select2.
    </p>

    <p>
      The adapters implement a consistent interface that is documented in the
      <a href="options.html#adapters">options section for adapters</a>, allowing
      you to customize Select2 to do exactly what you are looking for. Select2
      is designed such that you can mix and match plugins, with most of the core
      options being built as decorators that wrap the standard adapters.
    </p>
  </section>

  <section id="amd-builds">
    <h2>AMD-based build system</h2>

    <p>
      Select2 now uses an
      <a href="https://en.wikipedia.org/wiki/Asynchronous_module_definition">AMD-based build system</a>,
      allowing for builds that only require the parts of Select2 that you need.
      While a custom build system has not yet been created, Select2 is open
      source and will gladly accept a pull request for one.
    </p>

    <p>
      Select2 includes the minimal <a href="https://github.com/jrburke/almond">almond</a>
      AMD loader, but a custom <code>select2.amd.js</code> build is available
      if you already use an AMD loader. The code base (available in the
      <code>src</code> directory) also uses AMD, allowing you to include Select2
      in your own build system and generate your own builds alongside your
      existing infrastructure.
    </p>

    <p>
      The AMD methods used by Select2 are available as
      <code>jQuery.fn.select2.amd.define()/require()</code>, allowing you to use the
      included almond loader. These methods are primarily used by the
      translations, but they are the recommended way to access custom modules
      that Select2 provides.
    </p>
  </section>

  <section id="migrating">
    <h1>Migrating from Select2 3.5</h1>

    <p>
      There are a few breaking changes that migrators should be aware of when
      they are coming from older versions of Select2.
    </p>

    <p>
      If you use the full build of Select2 (<code>select2.full.js</code>), you
      will be automatically notified of the major breaking changes, and
      compatibility modules will be used in some cases to ensure that your code
      still behaves how you were expecting.
    </p>

    <h2 id="hidden-input">No more hidden input tags</h2>

    <p>
      In past versions of Select2, an <code>&lt;input type="hidden" /&gt;</code>
      tag was recommended if you wanted to do anything advanced with Select2,
      such as work with remote data sources or allow users to add their own
      tags. This had the unfortunate side-effect of servers not receiving the
      data from Select2 as an array, like a standard <code>&lt;select&gt;</code>
      element does, but instead sending a string containing the comma-separated
      strings. The code base ended up being littered with special cases for the
      hidden input, and libraries using Select2 had to work around the
      differences it caused.
    </p>

    <p>
      In Select2 4.0, the <code>&lt;select&gt;</code> element supports all core
      options, and support for the old
      <code>&lt;input type="hidden" /&gt;</code> has been removed. This means
      that if you previously declared an AJAX field with some pre-selected
      options that looked like...
    </p>

<pre class="prettyprint linenums">
&lt;input type="hidden" name="select-boxes" value="1,2,4,6" /&gt;
</pre>

    <p>
      Will need to be recreated as a <code>&lt;select&gt;</code> element with
      some <code>&lt;option&gt;</code> tags that have <code>value</code>
      attributes that match the old value.
    </p>

<pre class="prettyprint linenums">
&lt;select name="select-boxes" multiple="multiple"&gt;
  &lt;option value="1" selected="selected"&gt;Select2&lt;/option&gt;
  &lt;option value="2" selected="selected"&gt;Chosen&lt;/option&gt;
  &lt;option value="4" selected="selected"&gt;selectize.js&lt;/option&gt;
  &lt;option value="6" selected="selected"&gt;typeahead.js&lt;/option&gt;
&lt;/select&gt;
</pre>

    <p>
      The options that you create should have <code>selected="selected"</code>
      set so Select2 and the browser knows that they should be selected. The
      <code>value</code> attribute of the option should also be set to the value
      that will be returned from the server for the result, so Select2 can
      highlight it as selected in the dropdown. The text within the option
      should also reflect the value that should be displayed by default for the
      option.
    </p>

    <h2 id="new-matcher">Advanced matching of searches</h2>

    <p>
      In past versions of Select2, when matching search terms to individual
      options, which limited the control that you had when displaying results,
      especially in cases where there was nested data. The <code>matcher</code>
      function was only given the individual option, even if it was a nested
      options, without any context.
    </p>

    <p>
      With the new matcher function, only the root-level options are matched and
      matchers are expected to limit the results of any children options that
      they contain. This allows developers to customize how options within
      groups can be displayed, and modify how the results are returned.
    </p>

    <p>
      A function has been created that allows old-style matcher functions to be
      converted to the new style. You can retrieve the function from the
      <code>select2/compat/matcher</code> module, which should just wrap the old
      matcher function.
    </p>

    <h2 id="flexible-placeholders">More flexible placeholders</h2>

    <p>
      In the most recent versions of Select2, placeholders could only be
      applied to the first (typically the default) option in a
      <code>&lt;select&gt;</code> if it was blank. The
      <code>placeholderOption</code> option was added to Select2 to allow users
      using the <code>select</code> tag to select a different option, typically
      an automatically generated option with a different value.
    </p>

    <p>
      The <code>placeholder</code> option can now take an object as well as just
      a string. This replaces the need for the old
      <code>placeholderOption</code>, as now the <code>id</code> of the object
      can be set to the <code>value</code> attribute of the
      <code>&lt;option&gt;</code> tag.
    </p>

    <p>
      For a select that looks like the following, where the first option (with a
      value of <code>-1</code>) is the placeholder option...
    </p>

<pre class="prettyprint linenums">
&lt;select&gt;
  &lt;option value="-1" selected="selected"&gt;Select an option&lt;/option&gt;
  &lt;option value="1"&gt;Something else&lt;/option&gt;
&lt;/select&gt;
</pre>

    <p>
      You would have previously had to get the placeholder option through the
      <code>placeholderOption</code>, but now you can do it through the
      <code>placeholder</code> option by setting an <code>id</code>.
    </p>

<pre class="prettyprint linenums">
$("select").select2({
  placeholder: {
    id: "-1",
    placeholder: "Select an option"
  }
})
</pre>

    <p>
      And Select2 will automatically display the placeholder when the value of
      the select is <code>-1</code>, which it is by default. This does not break
      the old functionality of Select2 where the placeholder option was blank by
      default.
    </p>

    <h2 id="value-ordering">Display reflects the actual order of the values</h2>

    <p>
      In past versions of Select2, choices were displayed in the order that
      they were selected. In cases where Select2 was used on a
      <code>&lt;select&gt;</code> element, the order that the server recieved
      the selections did not always match the order that the choices were
      displayed, resulting in confusion in situations where the order is
      important.
    </p>

    <p>
      Select2 will now order selected choices in the same order that will be
      sent to the server.
    </p>

    <h2 id="changed-options">Changed method and option names</h2>

    <p>
      When designing the future option set for Select2 4.0, special care was
      taken to ensure that the most commonly used options were brought over.
      For the most part, the commonly used options of Select2 can still be
      referenced under their previous names, but there were some changes which
      have been noted.
    </p>

    <h3 id="removed-initselection">
      Removed the requirement of <code>initSelection</code>
    </h3>

    <p>
      In the past, whenever you wanted to use a custom data adapter, such as
      AJAX or tagging, you needed to help Select2 out in determining the initial
      values that were selected. This was typically done through the
      <code>initSelection</code> option, which took the underlying data of the
      input and converted it into data objects that Select2 could use.
    </p>

    <p>
      This is now handled by
      <a href="options.html#dataAdapter">the data adapter</a> in the
      <code>current</code> method, which allows Select2 to convert the currently
      selected values into data objects that can be displayed. The default
      implementation converts the text and value of <code>option</code> elements
      into data objects, and is probably suitable for most cases. An example of
      the old <code>initSelection</code> option is included below, which
      converts the value of the selected options into a data object with both
      the <code>id</code> and <code>text</code> matching the selected value.
    </p>

<pre class="prettyprint linenums">
initSelection : function (element, callback) {
  var data = [];
  $(element.val()).each(function () {
    data.push({id: this, text: this});
  });
  callback(data);
}
</pre>

    <p>
      When using the new <code>current</code> method of the custom data adapter,
      <strong>this method is called any time Select2 needs a list</strong> of
      the currently selected options. This is different from the old
      <code>initSelection</code> in that it was only called once, so it could
      suffer from being relatively slow to process the data (such as from a
      remote data source).
    </p>

<pre class="prettyprint linenums">
$.fn.select2.amd.require(
['select2/data/array', 'select2/utils'],
function (ArrayData, Utils) {
  function CustomData ($element, options) {
    CustomData.__super__.constructor.call(this, $element, options);
  }

  Utils.Extend(CustomData, ArrayData);

  CustomData.prototype.current = function (callback) {
    var data = [];
    var currentVal = this.$element.val();

    if (!this.$element.prop('multiple')) {
      currentVal = [currentVal];
    }

    for (var v = 0; v < currentVal.length; v++) {
      data.push({
        id: currentVal[v],
        text: currentVal[v]
      });
    }

    callback(data);
  };

  $("#select").select2({
    dataAdapter: CustomData
  });
}
</pre>

    <p>
      The new <code>current</code> method of the data adapter works in a similar
      way to the old <code>initSelection</code> method, with three notable
      differences. The first, and most important, is that <code>it is called
        whenever the current selections are needed</code> to ensure that Select2
        is always displaying the most accurate and up to date data. No matter
        what type of element Select2 is attached to, whether it supports a
        single or multiple selections, the data passed to the callback
        <strong>must be an array, even if it contains one selection</strong>.
        The last is that there is only one parameter, the callback to be
        executed with the latest data, and the current element that Select2 is
        attached to is available on the class itself as
        <code>this.$element</code>.
    </p>

    <h3 id="query-to-data-adapter">
      Custom data adapters instead of <code>query</code>
    </h3>

    <p>
      <a href="http://select2.github.io/select2/#data">In the past</a>, any time
      you wanted to hook Select2 up to a diferent data source you would be
      required to implement custom <code>query</code> and
      <code>initSelection</code> methods. This allowed Select2 to determine the
      initial selection and the list of results to display, and it would handle
      everything else internally, which was fine more most people.
    </p>

    <p>
      The custom <code>query</code> and <code>initSelection</code> methods have
      been replaced by
      <a href="options.html#dataAdapter">custom data adapters</a> that handle
      how Select2 stores and retrieves the data that will be displayed to the
      user. An example of the old <code>query</code> option is provided below,
      which is
      <a href="http://select2.github.io/select2/#data">the same as the old example</a>,
      and it generates results that contain the search term repeated a certain
      number of times.
    </p>

<pre class="prettyprint linenums">
query: function (query) {
  var data = {results: []}, i, j, s;
  for (i = 1; i < 5; i++) {
    s = "";
    for (j = 0; j < i; j++) {s = s + query.term;}
    data.results.push({id: query.term + i, text: s});
  }
  query.callback(data);
}
</pre>

    <p>
      This has been replaced by custom data adapters which define a similarly
      named <code>query</code> method. The comparable data adapter is provided
      below as an example.
    </p>

<pre class="prettyprint linenums">
$.fn.select2.amd.require(
['select2/data/array', 'select2/utils'],
function (ArrayData, Utils) {
  function CustomData ($element, options) {
    CustomData.__super__.constructor.call(this, $element, options);
  }

  Utils.Extend(CustomData, ArrayData);

  CustomData.prototype.query = function (params, callback) {
    var data = {
      results: []
    };

    for (var i = 1; i < 5; i++) {
      var s = "";

      for (var j = 0; j < i; j++) {
        s = s + params.term;
      }

      data.results.push({
        id: params.term + i,
        text: s
      });
    }

    callback(data);
  };

  $("#select").select2({
    dataAdapter: CustomData
  });
}
</pre>

    <p>
      The new <code>query</code> method of the data adapter is very similar to
      the old <code>query</code> option that was passed into Select2 when
      initializing it. The old <code>query</code> argument is mostly the same as
      the new <code>params</code> that are passed in to query on, and the
      callback that should be used to return the results is now passed in as the
      second parameter.
    </p>

    <h3 id="changed-templating">Renamed templating options</h3>

    <p>
      Select2 previously provided multiple options for formatting the results
      list and selected options, commonly referred to as "formatters", using the
      <code>formatSelection</code> and <code>formatResult</code> options. As the
      "formatters" were also used for things such as localization,
      <a href="#changed-translations">which has also changed</a>, they have been
      renamed to <code>templateSelection</code> and <code>templateResult</code>
      and their signatures have changed as well.
    </p>

    <p>
      You should refer to the updated
      <a href="options.html#templates">documentation on templates</a> when
      migrating from previous versions of Select2.
    </p>

    <h3 id="changed-id">
      The <code>id</code> and <code>text</code> properties are strictly enforced
    </h3>

    <p>
      When working with array and AJAX data in the past, Select2 allowed a
      custom <code>id</code> function or attribute to be set in various places,
      ranging from the initialization of Select2 to when the remote data was
      being returned. This allowed Select2 to better integrate with existing
      data sources that did not necessarily use the <code>id</code> attribute to
      indicate the unique identifier for an object.
    </p>

    <p>
      Select2 no longer supports a custom <code>id</code> or <code>text</code>
      to be used, but provides integration points for converting incorrect data
      to the expected format.
    </p>

    <h4>
      When working with array data
    </h4>

    <p>
      Select2 previously supported defining array data as an object that matched
      the signature of an AJAX response. A <code>text</code> property could be
      specified that would map the given property to the <code>text</code>
      property on the individual objects. You can now do this when initializing
      Select2 by using the following jQuery code to map the old
      <code>text</code> and <code>id</code> properties to the new ones.
    </p>

<pre class="prettyprint linenums">
var data = $.map([
  {
    pk: 1,
    word: 'one'
  },
  {
    pk: 2,
    word: 'two'
  }
], function (obj) {
  obj.id = obj.id || obj.pk;
  obj.text = obj.text || obj.word;

  return obj;
});
</pre>

    <p>
      This will result in an array of data objects that have the <code>id</code>
      properties that match the existing <code>pk</code> properties and
      <code>text</code> properties that match the existing <code>word</code>
      properties.
    </p>

    <h4>
      When working with remote data
    </h4>

    <p>
      The same code that was given above can be used in the
      <code>processResults</code> method of an AJAX call to map properties there
      as well.
    </p>

    <h3 id="changed-translations">Renamed translation options</h3>

    <p>
      In previous versions of Select2, the default messages provided to users
      could be localized to fit the language of the website that it was being
      used on. Select2 only comes with the English language by default, but
      provides
      <a href="options.html#language">community-contributed translations</a> for
      many common languages. Many of the formatters have been moved to the
      <code>language</code> option and the signatures of the formatters have
      been changed to handle future additions.
    </p>

    <h3 id="changed-data">
      Declaring options using <code>data-*</code> attributes
    </h3>

    <p>
      In the past, Select2 has only supported declaring a subset of options
      using <code>data-*</code> attributes. Select2 now supports declaring all
      options using the attributes, using
      <a href="options.html#data-attributes">the format specified in the documentation</a>.
    </p>

    <p>
      You could previously declare the URL that was used for AJAX requests using
      the <code>data-ajax-url</code> attribute. While Select2 still allows for
      this, the new attribute that should be used is the
      <code>data-ajax--url</code> attribute. Support for the old attribute will
      be removed in Select2 4.1.
    </p>

    <p>
      Although it was not documented, a list of possible tags could also be
      provided using the <code>data-select2-tags</code> attribute and passing in
      a JSON-formatted array of objects for tags. As the method for specifying
      tags has changed in 4.0, you should now provide the array of objects using
      the <code>data-data</code> attribute, which maps to
      <a href="options.html#data">the array data</a> option. You should also
      enable tags by setting <code>data-tags="true"</code> on the object, to
      maintain the ability for users to create their own options as well.
    </p>

    <p>
      If you previously declared the list of tags as...
    </p>

<pre class="prettyprint linenums">
&lt;select data-select2-tags="[{id: '1', text: 'One', id: '2', text: 'Two'}]"&gt;&lt;/select&gt;
</pre>

    <p>
      ...then you should now delare it as...
    </p>

<pre class="prettyprint linenums">
&lt;select data-data="[{id: '1', text: 'One', id: '2', text: 'Two'}]" data-tags="true"&gt;&lt;/select&gt;
</pre>

    <h2 id="removed-methods">Deprecated and removed methods</h2>

    <p>
      As Select2 now uses a <code>&lt;select&gt;</code> element for all data
      sources, a few methods that were available by calling
      <code>.select2()</code> are no longer required.
    </p>

    <h3>.select2("val")</h3>

    <p>
      The <code>"val"</code> method has been deprecated and will be removed in
      Select2 4.1. The deprecated method no longer includes the
      <code>triggerChange</code> parameter.
    </p>

    <p>
      You should directly call <code>.val</code> on the underlying
      <code>&lt;select&gt;</code> element instead. If you needed the second
      parameter (<code>triggerChange</code>), you should also call
      <code>.trigger("change")</code> on the element.
    </p>

<pre class="prettyprint linenums">
$("select").val("1"); // instead of $("select").select2("val", "1");
</pre>

    <h3>.select2("enable")</h3>

    <p>
      Select2 will respect the <code>disabled</code> property of the underlying
      select element. In order to enable or disable Select2, you should call
      <code>.prop('disabled', true/false)</code> on the
      <code>&lt;select&gt;</code> element. Support for the old methods will be
      completely removed in Select2 4.1.
    </p>

<pre class="prettyprint linenums">
$("select").prop("disabled", true); // instead of $("select").enable(false);
</pre>
  </section>
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