2011-02-07 07:48:44 +01:00
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# Requirements
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## Introduction
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The requirements class takes care of including CSS and JavaScript into your applications. This is preferred to
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hardcoding any references in the `<head>`-tag of your template, as it enables a more flexible handling.
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## Including inside PHP Code
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It is common practice to include most Requirements either in the *init()*-method of your [controller](/topics/controller), or
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as close to rendering as possible (e.g. in `[api:FormField]`
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:::php
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Requirements::javascript("cms/javascript/LeftAndMain.js");
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Requirements::css("cms/css/TreeSelector.css");
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If you're using the CSS method a second argument can be used. This argument defines the 'media' attribute of the `<link>`
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element, so you can define 'screen' or 'print' for example.
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Requirements::css("cms/css/TreeSelector.css", "screen,projection");
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## Including inside Template files
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If you do not want to touch the PHP (for example you are constructing a generic theme) then you can include a file via
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the templates
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<% require css(cms/css/TreeSelector.css) %>
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<% require themedCSS(TreeSelector) %>
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<% require javascript(cms/javascript/LeftAndMain.js) %>
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## Combining Files
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You can concatenate several CSS or javascript files into a single dynamically generated file. This increases performance
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reducing HTTP requests. Note that for debugging purposes combined files is disabled in devmode.
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:::php
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// supports CSS + JS
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Requirements::combine_files(
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'foobar.js',
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array(
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'mysite/javascript/foo.js',
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'mysite/javascript/bar.js',
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)
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);
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2013-03-21 19:48:54 +01:00
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By default it stores the generated file in the assets/ folder but you can configure this by pointing
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the `Requirements.combined_files_folder` configuration setting to a specific folder.
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2011-02-07 07:48:44 +01:00
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If SilverStripe doesn't have permissions on your server to write these files it will default back to including them
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individually .
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2013-02-12 22:54:53 +01:00
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You can also combine CSS files into a media-specific stylesheets as you would with the `Requirements::css` call - use
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the third paramter of the `combine_files` function:
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:::php
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$printStylesheets = array(
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"$themeDir/css/print_HomePage.css",
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"$themeDir/css/print_Page.css",
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);
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Requirements::combine_files('print.css', $printStylesheets, 'print');
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2011-02-07 07:48:44 +01:00
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## Custom Inline Scripts
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You can also quote custom script directly. This may seem a bit ugly, but is useful when you need to transfer some kind
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of 'configuration' from the database to the javascript/css. You'll need to use the "heredoc" syntax to quote JS and
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CSS, this is generally speaking the best way to do these things - it clearly marks the copy as belonging to a different
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language.
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:::php
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Requirements::customScript(<<<JS
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alert("hi there");
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JS
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);
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Requirements::customCSS(<<<CSS
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.tree li.$className {
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background-image: url($icon);
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}
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CSS
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);
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## Templated javascript
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A variant on the inclusion of custom javascript is the inclusion of *templated* javascript. Here, you keep your
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JavaScript in a separate file and instead load, via search and replace, several PHP-generated variables into that code.
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:::php
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$vars = array(
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"EditorCSS" => "mot/css/editor.css",
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)
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Requirements::javascriptTemplate("cms/javascript/editor.template.js", $vars);
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## Clearing
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You may want to clear all of the requirements mentioned thus far. I've used this when you've put an iframe generator as
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an action on the controller that uses it. The iframe has a completely different set of scripting and styling
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requirements, and it's easiest to flush all the default stuff and start again.
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:::php
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Requirements::clear();
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You can also clear specific Requirements:
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:::php
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Requirements::clear('jsparty/prototype.js');
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Caution: Depending on where you call this command, a Requirement might be *re-included* afterwards.
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## Inclusion Order
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Requirements acts like a stack, where everything is rendered sequentially in the order it was included. There is no way
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to change inclusion-order, other than using *Requirements::clear* and rebuilding (=guessing) the whole set of
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requirements. Caution: Inclusion order is both relevant for CSS and Javascript files in terms of dependencies,
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inheritance and overlays - please be careful when messing with the order of Requirements.
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NOTE:
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By default, SilverStripe includes all Javascript files at the bottom of the page body. If this causes problems for you,
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for example if you're using animation that ends up showing everything until the bottom of the page loads, or shows
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2013-03-21 19:48:54 +01:00
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buttons before pushing them will actually work, you can change this behaviour through
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the `Requirements.write_js_to_body` configuration setting.
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2011-02-07 07:48:44 +01:00
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## CMS Requirements
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2011-03-08 22:05:51 +01:00
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The SilverStripe core includes a lot of Requirements by itself. Most of these are collated in `[api:LeftAndMain]` first.
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2011-02-07 07:48:44 +01:00
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## Motivation
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Every page requested is made up of a number of parts, and many of those parts require their own CSS or JavaScript.
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Rather than force the developer to put all of those requests into the template, or the header function, you can
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reference required files anywhere in your application.
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This lets you create very modular units of PHP+JavaScript+CSS, which a powerful concept but must be managed carefully.
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## Managing Generic CSS styling
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One of the aims of this is to create units of functionality that can be reasonably easily deployed as-is, while still
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giving developers the option to customise them. The logical solution to this is to create 'generic' CSS to be applied
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to these things. However, we must take great care to keep the CSS selectors very nonspecific. This precludes us from
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adding any CSS that would "override customisations" in the form - for example, resetting the width of a field where 100%
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width isn't appropriate.
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Another solution would be to include some "generic CSS" for form elements at the very high level, so that fixed widths
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on forms were applied to the generic form, and could therefore be overridden by a field's generic stylesheet. Similar
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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
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one.
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Perhaps we could make use of a Requirements::disallowCSS() function, with which we could prevent the standard CSS from
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being included in situations where it caused problems. But the complexity could potentially balloon, and really, it's a
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bit of an admission of defeat - we shouldn't need to have to do this if our generic CSS was well-designed.
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## Ideas/Problems
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### Ajax
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The whole "include it when you need it" thing shows some weaknesses in areas such as the CMS, where Ajax is used to load
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in large pieces of the application, which potentially require more CSS and JavaScript to be included. At this stage,
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the only workaround is to ensure that everything you might need is included on the first page-load.
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One idea is to mention the CSS and JavaScript which should be included in the header of the Ajax response, so that the
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client can load up those scripts and stylesheets upon completion of the Ajax request. This could be coded quite
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cleanly, but for best results we'd want to extend prototype.js with our own changes to their Ajax system, so that every
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script had consistent support for this.
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### Lots of files
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Because everything's quite modular, it's easy to end up with a large number of small CSS and JavaScript files. This has
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problems with download time, and potentially maintainability.
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We don't have any easy answers here, but here are some ideas:
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* Merging the required files into a single download on the server. The flip side of this is that if every page has a
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slightly different JS/CSS requirements, the whole lot will be refetched.
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* Better: "Tagging" each required file for different use-cases, and creating a small set of common functionalities
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(e.g. everything tagged "base" such as prototype.js would always be included)
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* Do lazy fetching of scripts within an ajax-call. This seems to be possible, but very tricky due to the asynchronous
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nature of an ajax-request. Needs some more research
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## API Documentation
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`[api:Requirements]`
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