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Autocomplete JavaScript

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From a backend perspective, the custom field is done! When the user submits a string email address, the data transformer turns that into the proper User object, with built-in validation.

But from a frontend perspective, it could use some help. It would be way more awesome if this field had some cool JavaScript auto-completion magic where it suggested valid emails as I typed. So... let's do it!

Google for "Algolia autocomplete". There are a lot of autocomplete libraries, and this one is pretty nice. Click into their documentation and then to the GitHub page for autocomplete.js.

Many of you might know that Symfony comes with a great a JavaScript tool called Webpack Encore, which helps you create organized JavaScript and build it all into compiled files. We have not been using Encore in this tutorial yet. So I'm going to keep things simple and continue without it. Don't worry: the most important part of what we're about to do is the same no matter what: it's how you connect custom JavaScript to your form fields.

Adding the autocomplete.js JavaScript

Copy the script tag for jQuery, open templates/article_admin/edit.html.twig and override {% block javascripts %} and {% endblock %}. Call the {{ parent() }} function to keep rendering the parent JavaScript. Then paste in that new <script> tag.

23 lines | templates/article_admin/edit.html.twig
// ... lines 1 - 2
{% block javascripts %}
{{ parent() }}
<script src="https://cdn.jsdelivr.net/autocomplete.js/0/autocomplete.jquery.min.js"></script>
// ... line 7
{% endblock %}
// ... lines 9 - 23

Yes, we are also going to need to do this in the new template. We'll take care of that in a little bit.

Now, if you scroll down a little on their docs... there it is! This page has some CSS that helps make all of this look good. Copy that, go to the public/css directory, and create a new file: algolia-autocomplete.css. Paste this there.

Include this file in our template as well: override {% block stylesheets %} and {% endblock %}. This time add a <link> tag that points to that file: algolia-autocomplete.css. Oh, and don't forget the parent() call - I'll add that in a second.

23 lines | templates/article_admin/edit.html.twig
// ... lines 1 - 9
{% block stylesheets %}
{{ parent() }}
<link rel="stylesheet" href="{{ asset('css/algolia-autocomplete.css') }}">
{% endblock %}
// ... lines 15 - 23

Finally, for the custom JavaScript logic, in the js/ directory, create a new file called algolia-autocomplete.js. Before I fill anything in here, include that in the template: a <script> tag pointing to js/algolia-autocomplete.js.

23 lines | templates/article_admin/edit.html.twig
// ... lines 1 - 2
{% block javascripts %}
// ... lines 4 - 6
<script src="{{ asset('js/algolia-autocomplete.js') }}"></script>
{% endblock %}
// ... lines 9 - 23

Implementing autocomplete.js

Initial setup done! Head back to their documentation to find where it talks about how to use this with jQuery. It looks kinda simple: select an element, call .autcomplete() on it, then... pass a ton of options that tell it how to fetch and process the autocomplete data.

Cool! Let's do something similar! I'll start with the document.ready() block from jQuery just to make sure the DOM is fully loaded. Now: here is the key moment: how can we write JavaScript that can connect to our custom field? Should we select it by the id? Something else?

I like to select with a class. Find all elements with, how about, some .js-user-autocomplete class. Nothing has this class yet, but our field will soon. Call .autocomplete() on this, pass it that same hint: false and then an array. This looks a bit complex: add a JavaScript object with a source option set to a function() that receives a query argument and a callback cb argument.

Basically, as we're typing in the text field, the library will call this function and pass whatever we've entered into the text box so far as the query argument. Our job is to determine which results match this "query" text and pass those back by calling the cb function.

To start... let's hardcode something and see if it works! Call cb() and pass it an array where each entry is an object with a value key... because that's how the library wants the data to be structured by default.

$(document).ready(function() {
$('.js-user-autocomplete').autocomplete({hint: false}, [
source: function(query, cb) {
{value: 'foo'},
{value: 'bar'}

Thanks to my imaginative code, no matter what we type, foo and bar should be suggested.

Adding the js- Class to the Field

And... we're almost... sorta done! In order for this to be applied to our field, all we need to do is add this class to the author field. No problem! Copy the class name and open UserSelectTextType. Here, we can set a default value for the attr option to an array with class set to js-user-autocomplete.

47 lines | src/Form/UserSelectTextType.php
// ... lines 1 - 11
class UserSelectTextType extends AbstractType
// ... lines 14 - 33
public function configureOptions(OptionsResolver $resolver)
// ... lines 37 - 40
'attr' => [
'class' => 'js-user-autocomplete'

Field Options vs View Variables

Up until now, if we've wanted to add a class attribute, we've done it from inside of our Twig template. For example, open security/register.html.twig. For the form start tag, we're passing an attr variable with a class key. Or, for the fields, we're adding a placeholder attribute.

attr is one of a few things that can be passed either as a view variable or also as a field option. But, I want to be clear: options and variables are two different things. Go back and open the profiler. Click on, how about, the author field. We know that there is a set of options that we can pass to the field from inside the form class. And then, when you're rendering in your template, there is a different set of view variables. These are two different concepts. However, there is some overlap, like attr.

Behind the scenes, when you pass the attr option, that simply becomes the default value for the attr view variable. The attr option, just like the label and help options - exists just for the added convenience of being able to set these in your form class or in your template.

Anyways, thanks to the code in UserSelectTextType, our field should have this class. Let's try it! Close the profiler, refresh and... ah! I killed my page! The CSS is gone! I always do that! Go back to the template and add the missing parent() call: I don't want to completely replace the CSS from our layout.

Ok, try it again. Much better. And when we type into the field... yes! We get foo and bar no matter what we type. Awesome!

Next, hey: I like foo and bar as much as the next programmer. But we should probably make an AJAX call to fetch a true list of matching email addresses.