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Extra Credit Tricks and HTML Escaping

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Keep on Learning!

You're a pro now, so let's have a little fun and see some sweet tricks!

Expert Control of Blocks with the block Function

We've learned a lot about template inheritance and blocks. Now, let's make things a bit more interesting. We created a title block in our layout so that individual pages could control the page title. If a page has a title block, it replaces the page title entirely. If it has no title block, then the default title is used.

Let me change the title block to be a little more interesting:

    {% block title %}
        Penguins Pants Plus! Your source for fancy penguin suits
    {% endblock %} | Penguins Pants Plus!

My goal is to suffix the page title with "Penguins Pants Plus!" so that all of our pages are consistent. The only funny thing here, besides penguin pants, is that if the title block isn't overridden, the suffix is a little redundant. Is it possible to only add the extra text if the title block is overridden?

The secret is the block function, which you can use to return the content of a block at any time. Replace the traditional {% block title %} and instead use the block() function in a say something tag:

{{ block('title') }} | Penguins Pants Plus!

When we refresh, this works like before: the block function prints out the content from the title block. The only thing we're missing is the default page title if the title block isn't set.

Now that we know about this block function, we can do that easily with an if statement:

{% if block('title') %}
    {{ block('title') }} | Penguins Pants Plus!
{% else %}
    Penguins Pants Plus! Your source for fancy penguin suits
{% endif %}


The block() function throws an exception since Twig 2.0 if there's no block with specified name. At first, be sure that the block is defined:

{% if block('title') is defined %}
    {{ block('title') }} | Penguins Pants Plus!
{% else %}
    Penguins Pants Plus! Your source for fancy penguin suits
{% endif %}

Success! When we override the title block on the homepage, we get the suffix added. But on the contact page, we just get the default page title. I try to use blocks in their traditional fashion as often as possible. But when things get more complicated, use the block function to do some really custom things.

Go Deeper!

To get really advanced, you can import blocks from other templates and use them in this way. See the use tag for more details.

The Short block Syntax

And while we're on this topic, we can make the title block even shorter in homepage.twig:

{% block title 'Start looking fly!' %}

You're free to choose whatever format you want, but if your block is just a simple string, you'll often see this version used.

Concatenating Strings

One apparent drawback to this is that you can't mix static text and variables like you could before by just writing some text and then using the "say something" syntax.

For example, suppose we wanted to include the pageData.title variable in the page title. How can we combine it with the static text? The answer is with the ~ character, which concatenates strings in Twig.

{% block title 'Start looking fly! '~pageData.title %}

You won't see this too often, but it'll come in handy when you need it.

Whitespace Control

Normally, the whitespace you put in a Twig file is left completely alone. We can see this when we view the source. In fact, we have some extra space around the title tag because of the new trick we're using in Twig. Let's see if we can get rid of it!

On any twig starting or ending tag, you can add a minus sign (-):

    {%- if block('title') %}
        {{ block('title') }} | Penguins Pants Plus!
    {% else %}
        Penguins Pants Plus! Your source for fancy penguin suits
    {% endif %}

This tells Twig to trim all the whitespace to the left of that tag until it hits a non-whitespace character. When we view the source, we can see a slightly smaller amount of whitespace. If we add enough of these, we'll see all the extra space disappear:

    {%- if block('title') -%}
        {{- block('title') -}} | Penguins Pants Plus!
    {%- else -%}
        Penguins Pants Plus! Your source for fancy penguin suits
    {%- endif -%}

The spaceless Tag

Another way to control whitespace is with the spaceless tag. The point of this tag is a little different: it removes all whitespace between HTML tags, without affecting space inside an HTML tag or inside static text. If we surround the meta tags with this and refresh, we'll see those meta tags all print right next to each other on one line:

{% spaceless %}
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="description" content="">
<meta name="author" content="">
{% endspaceless %}

Using Undefined Variables with the default Filter

Let's see one more common trick that may look strange when you first see it. Look back in the banner.twig template where we used the single-line if syntax. Actually, there's an easier way to do this by using the default filter:

<div class="well" style="background-color: {{ backgroundColor|default('lightblue') }};">

Normally, if you reference an undefined variable in Twig, it blows up! But when you use the default filter, it avoids that error and instead, returns the default value lightblue. You may see this trick quite often when someone is using a variable that may or may not be defined.


Depending on your settings, Twig may just fail silently if you reference an undefined variable.


Ok, one last thing - HTML escaping! Whenever you render content that may have been filled in by the user, you need to escape it. This prevents people from writing HTML tags that you don't want or, worse, JavaScript code that could be used for cross-site scripting attacks. That's scarier than a hungry pack of leopard seals!

Let's try this out by adding some HTML markup to our page summary:

// index.php
// ...

echo $twig->render('homepage.twig', array(
    'pageData' => array(
        'summary'   => "You're <strong>hip</strong>, you're cool ...",
    // ...

When we refresh, Twig is automatically escaping these characters and printing them out safely. Actually, whether or not Twig automatically does this depends on how it's setup. In your case, try this out and see if Twig is escaping or not escaping automatically. You can try this easily by printing out a static string and seeing what happens.

{{ '<strong>hallo</strong>'|upper }}

In some cases, you may need to actually print out some content unescaped. To do this, just use the handy raw filter:

    {{ pageData.summary|raw }}


If automatic escaping is off, then you need to be quite careful and use the escape filter on any strings you print out to make sure they are escaped.

Happy Trails

Well hello Twig expert! Our time talking about Twig is coming to an end, but the good news is that you have all the tools you need to be successful and your penguins are looking dapper. Remember that all the tags, functions, filters and tests that are available in Twig can be found on the bottom of its documentation page.

Also remember that in your project, you may have even more tags, functions, filters or tests that are specific to you. Your challenge from here is to find out what those are and what secrets each holds.

Good luck, and seeya next time!