NAME

HTML::DeferableCSS - Simplify management of stylesheets in your HTML

VERSION

version v0.4.2

SYNOPSIS

use HTML::DeferableCSS;

my $css = HTML::DeferableCSS->new(
    css_root      => '/var/www/css',
    url_base_path => '/css',
    inline_max    => 512,
    simple  => 1,
    aliases => {
      reset => 1,
      jqui  => 'jquery-ui',
      site  => 'style',
    },
    cdn => {
      jqui  => '//cdn.example.com/jquery-ui.min.css',
    },
);

$css->check or die "Something is wrong";

...

print $css->deferred_link_html( qw[ jqui site ] );

DESCRIPTION

This is an experimental module for generating HTML-snippets for deferable stylesheets.

This allows the stylesheets to be loaded asynchronously, allowing the page to be rendered faster.

Ideally, this would be a simple matter of changing stylesheet links to something like

<link rel="preload" as="stylesheet" href="....">

but this is not well supported by all web browsers. So a web page needs to use some JavaScript to handle this, as well as a noscript block as a fallback.

This module allows you to simplify the management of stylesheets for a web application, from development to production by

• declaring all stylesheets used by your web application;
• specifying remote aliases for stylesheets, e.g. from a CDN;
• enable or disable the use of minified stylesheets;
• switch between local copies of stylesheets or CDN versions;
• automatically inline small stylesheets;
• use deferred-loading stylesheets, which requires embedding JavaScript code as a workaround for web browsers that do not support these natively.

ATTRIBUTES

aliases

This is a required hash reference of names and their relative filenames to "css_root".

It is recommended that the .css and .min.css suffixes be omitted.

If the name is the same as the filename (without the extension) than you can simply use 1. (Likewise, an empty string or 0 disables the alias:

my $css = HTML::DeferableCSS->new(
  aliases => {
      reset => 1,
      gone  => 0,       # "gone" will be silently ignored
      one   => "1.css", #
  }
  ...
);

If all names are the same as their filenames, then an array reference can be used:

my $css = HTML::DeferableCSS->new(
  aliases => [ qw( foo bar } ],
  ...
);

If an alias is disabled, then it will simply be ignored, e.g.

$css->deferred_link_html('gone')

Returns an empty string. This allows you to disable a stylesheet in your configuration without having to remove all references to it.

Absolute paths cannot be used.

You may specify URLs instead of files, but this is not recommended, except for cases when the files are not available locally.

css_root

This is the required root directory where all stylesheets can be found.

url_base_path

This is the URL prefix for stylesheets.

It can be a full URL prefix.

prefer_min

If true (default), then a file with the .min.css suffix will be preferred, if it exists in the same directory.

Note that this does not do any minification. You will need separate tools for that.

css_files

This is a hash reference used internally to translate "aliases" into the actual files or URLs.

If files cannot be found, then it will throw an error. (See "check").

cdn_links

This is a hash reference of "aliases" to URLs. (Only one URL per alias is supported.)

When "use_cdn_links" is true, then these URLs will be used instead of local versions.

has_cdn_links

This is true when there are "cdn_links".

use_cdn_links

When true, this will prefer CDN URLs instead of local files.

inline_max

This specifies the maximum size of an file to inline.

Local files under the size will be inlined using the "link_or_inline_html" or "deferred_link_html" methods.

Setting this to 0 disables the use of inline links, unless "inline_html" is called explicitly.

defer_css

True by default.

This is used by "deferred_link_html" to determine whether to emit code for deferred stylesheets.

include_noscript

When true, a noscript element will be included with non-deffered links.

This defaults to the same value as "defer_css".

preload_script

This is the pathname of the cssrelpreload.js file that will be embedded in the resulting code.

The script comes from https://github.com/filamentgroup/loadCSS.

You do not need to modify this unless you want to use a different script from the one included with this module.

link_template

This is a code reference for a subroutine that returns a stylesheet link.

preload_template

This is a code reference for a subroutine that returns a stylesheet preload link.

asset_id

This is an optional static asset id to append to local links. It may refer to a version number or commit-id, for example.

This is useful to ensure that changes to stylesheets are picked up by web browsers that would otherwise use cached copies of older versions of files.

has_asset_id

True if there is an "asset_id".

log

This is a code reference for logging errors and warnings:

$css->log->( $level => $message );

By default, this is a wrapper around Carp that dies when the level is "error", and emits a warning for everything else.

You can override this so that errors are treated as warnings,

log => sub { warn $_[1] },

or that warnings are fatal,

log => sub { die $_[1] },

or even integrate this with your own logging system:

log => sub { $logger->log(@_) },

simple

When true, this enables a simpler method of using deferable CSS, without the need for the loadCSS script.

It is false by default, for backwards compatability. But it is recommended that you set this to true.

See https://www.filamentgroup.com/lab/load-css-simpler/.

This attribute was added in v0.4.0.

METHODS

check

This method instantiates lazy attributes and performs some minimal checks on the data. (This should be called instead of "css_files".)

It will throw an error or return false (depending on "log") if there is something wrong.

This was added in v0.3.0.

href

my $href = $css->href( $alias );

This returns this URL for an alias.

link_html

my $html = $css->link_html( $alias );

This returns the link HTML markup for the stylesheet referred to by $alias.

inline_html

my $html = $css->inline_html( $alias );

This returns an embedded stylesheet referred to by $alias.

link_or_inline_html

my $html = $css->link_or_inline_html( @aliases );

This returns either the link HTML markup, or the embedded stylesheet, if the file size is not greater than "inline_max".

Note that a stylesheet will be inlined, even if there is are "cdn_links".

deferred_link_html

my $html = $css->deferred_link_html( @aliases );

This returns the HTML markup for the stylesheets specified by "aliases", as appropriate for each stylesheet.

If the stylesheets are not greater than "inline_max", then it will embed them. Otherwise it will return the appropriate markup, depending on "defer_css".

KNOWN ISSUES

Content-Security-Policy (CSP)

If a web site configures a Content-Security-Policy setting to disable all inlined JavaScript, then the JavaScript shim will not work.

XHTML Support

This module is written for HTML5.

It does not support XHTML self-closing elements or embedding styles and scripts in CDATA sections.

Encoding

All files are embedded as raw files.

No URL encoding is done on the HTML links or "asset_id".

It's spelled "Deferrable"

It's also spelled "Deferable".

SOURCE

The development version is on github at https://github.com/robrwo/HTML-DeferableCSS and may be cloned from git://github.com/robrwo/HTML-DeferableCSS.git

BUGS

Please report any bugs or feature requests on the bugtracker website https://github.com/robrwo/HTML-DeferableCSS/issues

When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.

Please report any bugs in cssrelpreload.js to https://github.com/filamentgroup/loadCSS/issues.

AUTHOR

Robert Rothenberg rrwo@cpan.org

This module was developed from work for Science Photo Library https://www.sciencephoto.com.

reset.css comes from http://meyerweb.com/eric/tools/css/reset/.

cssrelpreload.js comes from https://github.com/filamentgroup/loadCSS/.

COPYRIGHT AND LICENSE

This software is Copyright (c) 2020 by Robert Rothenberg.

This is free software, licensed under:

The MIT (X11) License