Add Critical CSS to hexo to help improve render speed of a hexo site
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README.md

Hexo Critical CSS

A Hexo wrapper filter for critical.

Installation

npm install --save hexo-critical-css

Motivation

Speed up the initial load of your Hexo website.

Ensure critical parts of your CSS are within the HTML page, and then load your full CSS file in a defered manner.

Configuration

This respects skip_render to not run critical on anything that matches skip render.

critical

Purpose

The options object that would be given to critical.generate

Type

object, the options that are defined by critical.

This is mostly a pass-through so we limit the coupling that this library and critical has, so critical options can change with minimal impact on hexo-critical-css.

Special cases for critical paramters that affect hexo-critical-css

parameter effect on hexo-critical-css
inline Changes the way that hexo-critical-css injects the CSS into the HTML. If true, hexo-critical-css will trust the generated HTML and ignore the settings htmlTagToReplace, replacementHtmlHeader and replacementHtmlTrailer. If false, hexo-critical-css will inject the critical CSS using htmlTagToReplace, replacementHtmlHeader and replacementHtmlTrailer.

Special cases for critical paramters that are not passed through

parameter reason parameter is ignored
base hexo-critical-css library determines base for itself.
dest hexo-critical-css library cannot cope with dest (yet)
src hexo-critical-css library determines src for itself.

See also

Example

Add this rule in _config.yml to ensure critical minify options is set.

criticalcss:
  critical:
    minify: true

enable

Purpose

Use a configuration option to turn off hexo-critical-css.

Type

boolean, true will enable hexo-critical-css.

Example

Add this rule in _config.yml to enable hexo-critical-css

criticalcss:
  enable: true

htmlTagToReplace

Purpose

The expression used to search the HTML document for a token or HTML tag to inject the critical CSS into

Type

regular expression string, suitable to be passed into new RegExp(htmlTagToReplace).

See also

Example

Add this rule in _config.yml to match the closing </head> of the HTML file.

criticalcss:
  htmlTagToReplace: "</\\s*head>"

perPageCss

Purpose

There is difference of opinion on whether a CSS asset should be defined as site-wide, or per-page. This option allows you to choose which policy you wish to adopt.

Adopting a per-page implementation means that you will have a css directory in each of your subdirectories in your public directory that has an HTML file within it. Adopting a site-wide implementation means that you will have one css directory in public.

The default is site-wide implementation.

Type

boolean

Example

Add this rule in _config.yml to adopt per-page CSS implementation.

criticalcss:
  perPageCss: true

priority

Purpose

Allows hexo-critical-css to be run in a different order in regards to other filters.

Type

integer

See also

https://hexo.io/api/filter.html

Example

Add this rule in _config.yml to adjust the priority

criticalcss:
  priority: 10000

replacementHtmlHeader

Purpose

When injecting the critical CSS into the HTML document, it may be useful to have a prefix.

Type

string, which the critical CSS will be prefixed with

See also

Example

Add this rule in _config.yml to prepend the critical CSS output with.

criticalcss:
  replacementHtmlHeader: "<style type=\"text/css\">"

replacementHtmlTrailer

Purpose

When injecting the critical CSS into the HTML document, it may be useful to have a suffix.

Type

string, which the critical CSS will be suffixed with

See also

Example

Add this rule in _config.yml to postpend the critical CSS output with.

criticalcss:
  replacementHtmlTrailer: "</style></head>"

TODO

This was written very quickly as I needed it for another project I am undertaking. This means that I have work still to do. At least:

  • Find a way to allow critical dest option to be passed through.
  • Seek a way to get the inline deferred CSS link to not use inline scripts to be compatible with CSP rules preventing inline scripts.
  • Provide coding style guides
  • Move to an ECMA6 structure for future-proofing
  • Add babel as a pre-publish step to ensure current compatibility
  • Add example of best way to implement CSS in a theme

License

Copyright (c) 2016, John Whitley All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

  • Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

  • Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

  • Neither the name of hexo-critical-css nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.