Introduction

The requirements class takes care of including CSS and JavaScript into your applications. This is preferred to hardcoding any references in the <head>-tag of your template, as it enables a more flexible handling.

Usage

Including inside PHP Code

It is common practice to include most Requirements either in the init()-method of your controller, or as close to rendering as possible (e.g. in FormField→renderWith())

Requirements::javascript("cms/javascript/LeftAndMain.js");
Requirements::css("cms/css/TreeSelector.css");

If you’re using the CSS method a second argument can be used. This argument defines the ‘media’ attribute of the <link> element, so you can define ‘screen’ or ‘print’ for example.

Requirements::css("cms/css/TreeSelector.css", "screen,projection");

Including inside Template files

If you do not want to touch the PHP (for example you are constructing a generic theme) then you can include a file via the templates

<% require css(cms/css/TreeSelector.css) %>
<% require themedCSS(TreeSelector) %>
<% require javascript(cms/javascript/LeftAndMain.js) %>

Note that currently (as of 2.3) you cannot pass a second parameter to a function via the template parser so doing the following will not work.

<% require css(cms/css/TreeSelector.css, 'screen,projection') %>

Custom Inline Scripts

You can also quote custom script directly. This may seem a bit ugly, but is useful when you need to transfer some kind of ‘configuration’ from the database to the javascript/css. You’ll need to use the “heredoc” syntax to quote JS and CSS, this is generally speaking the best way to do these things - it clearly marks the copy as belonging to a different language.

Requirements::customScript(<<<JS
  alert("hi there"); 
JS
);
Requirements::customCSS(<<<CSS
  .tree li.$className {
    background-image: url($icon);
  }
CSS
);

Templated javascript

A variant on the inclusion of custom javascript is the inclusion of templated javascript. Here, you keep your JavaScript in a separate file and instead load, via search and replace, several PHP-generated variables into that code.

$vars = array(
    "EditorCSS" => "mot/css/editor.css",
)
Requirements::javascriptTemplate("cms/javascript/editor.template.js", $vars);

Clearing

You may want to clear all of the requirements mentioned thus far. I’ve used this when you’ve put an iframe generator as an action on the controller that uses it. The iframe has a completely different set of scripting and styling requirements, and it’s easiest to flush all the default stuff and start again.

Requirements::clear();

You can also clear specific Requirements:

Requirements::clear('jsparty/prototype.js');

Caution: Depending on where you call this command, a Requirement might be re-included afterwards.

Inclusion Order

Requirements acts like a stack, where everything is rendered sequentially in the order it was included. There is no way to change inclusion-order, other than using Requirements::clear and rebuilding (=guessing) the whole set of requirements. Caution: Inclusion order is both relevant for CSS and Javascript files in terms of dependencies, inheritance and overlays - please be careful when messing with the order of Requirements.

CMS Requirements

The Silverstripe core includes a lot of Requirements by itself. Most of these are collated in LeftAndMain→init(). If you want to add/remove Requirements in your LeftAndMain-subclass, make sure to call parent::init() first.

Motivation

Every page requested is made up of a number of parts, and many of those parts require their own CSS or JavaScript. Rather than force the developer to put all of those requests into the template, or the header function, you can reference required files anywhere in your application.

This lets you create very modular units of PHP+JavaScript+CSS, which a powerful concept but must be managed carefully.

Managing Generic CSS styling

One of the aims of this is to create units of functionality that can be reasonably easily deployed as-is, while still giving developers the option to customise them. The logical solution to this is to create ‘generic’ CSS to be applied to these things. However, we must take great care to keep the CSS selectors very nonspecific. This precludes us from adding any CSS that would “override customisations” in the form - for example, resetting the width of a field where 100% width isn’t appropriate.

Another solution would be to include some “generic CSS” for form elements at the very high level, so that fixed widths on forms were applied to the generic form, and could therefore be overridden by a field’s generic stylesheet. Similar to this is mandating the use of “form div.field input” to style form input tags, whether it’s a generic form or a custom one.

Perhaps we could make use of a Requirements::disallowCSS() function, with which we could prevent the standard CSS from being included in situations where it caused problems. But the complexity could potentially balloon, and really, it’s a bit of an admission of defeat - we shouldn’t need to have to do this if our generic CSS was well-designed.

Ideas/Problems

Ajax

The whole “include it when you need it” thing shows some weaknesses in areas such as the CMS, where Ajax is used to load in large pieces of the application, which potentially require more CSS and JavaScript to be included. At this stage, the only workaround is to ensure that everything you might need is included on the first page-load.

One idea is to mention the CSS and JavaScript which should be included in the header of the Ajax response, so that the client can load up those scripts and stylesheets upon completion of the Ajax request. This could be coded quite cleanly, but for best results we’d want to extend prototype.js with our own changes to their Ajax system, so that every script had consistent support for this.

Lots of files

Because everything’s quite modular, it’s easy to end up with a large number of small CSS and JavaScript files. This has problems with download time, and potentially maintainability.

We don’t have any easy answers here, but here are some ideas:

Merging the required files into a single download on the server. The flip side of this is that if every page has a slightly different JS/CSS requirements, the whole lot will be refetched.
Better: “Tagging” each required file for different use-cases, and creating a small set of common functionalities (e.g. everything tagged “base” such as prototype.js would always be included)
Do lazy fetching of scripts within an ajax-call. This seems to be possible, but very tricky due to the asynchronous nature of an ajax-request. Needs some more research

API Documentation

Full method documentation available here