Running KaTeX on Jekyll?

Are a couple of days that I'm trying to use KaTeX instead of MathJax on my static Jekyll website. I tried a lot of suggestion found on internet without success. The last one is the jekyll-katex plugin. I followed all the steps in the readme.

This is my current Gemfile:

source "https://rubygems.org"

gem "jekyll", "~> 3.8.3"
gem "minima", "~> 2.0"

group :jekyll_plugins do
  gem "jekyll-feed", "~> 0.6"
  gem 'jekyll-katex', "~> 0.2"
end

# Windows does not include zoneinfo files, so bundle the tzinfo-data gem
gem "tzinfo-data", platforms: [:mingw, :mswin, :x64_mingw, :jruby]

# Performance-booster for watching directories on Windows
gem "wdm", "~> 0.1.0" if Gem.win_platform?

This is the relevant part in my current _config.yml:

markdown: kramdown
theme: minima
plugins:
  - jekyll-feed
  - jekyll-katex

When I run bundle exec jekyll serve I receive this error:

bundler: failed to load command: jekyll (/usr/local/bin/jekyll)
Bundler::GemRequireError: There was an error while trying to load the gem 'jekyll-katex'.
Gem Load Error is: undefined method `[]' for nil:NilClass
Backtrace for gem load error is:
/var/lib/gems/2.5.0/gems/jekyll-katex-0.2.0/lib/jekyll-katex/configuration.rb:22:in `js_path'
/var/lib/gems/2.5.0/gems/jekyll-katex-0.2.0/lib/jekyll/tags/katex.rb:14:in `<class:Katex>'
/var/lib/gems/2.5.0/gems/jekyll-katex-0.2.0/lib/jekyll/tags/katex.rb:12:in `<module:Tags>'
/var/lib/gems/2.5.0/gems/jekyll-katex-0.2.0/lib/jekyll/tags/katex.rb:7:in `<module:Jekyll>'
/var/lib/gems/2.5.0/gems/jekyll-katex-0.2.0/lib/jekyll/tags/katex.rb:6:in `<top (required)>'
/var/lib/gems/2.5.0/gems/jekyll-katex-0.2.0/lib/jekyll-katex.rb:7:in `require'
/var/lib/gems/2.5.0/gems/jekyll-katex-0.2.0/lib/jekyll-katex.rb:7:in `<top (required)>'
/usr/local/lib/site_ruby/2.5.0/bundler/runtime.rb:81:in `require'
/usr/local/lib/site_ruby/2.5.0/bundler/runtime.rb:81:in `block (2 levels) in require'
/usr/local/lib/site_ruby/2.5.0/bundler/runtime.rb:76:in `each'
/usr/local/lib/site_ruby/2.5.0/bundler/runtime.rb:76:in `block in require'
/usr/local/lib/site_ruby/2.5.0/bundler/runtime.rb:65:in `each'
/usr/local/lib/site_ruby/2.5.0/bundler/runtime.rb:65:in `require'
/usr/local/lib/site_ruby/2.5.0/bundler.rb:114:in `require'
/var/lib/gems/2.5.0/gems/jekyll-3.8.3/lib/jekyll/plugin_manager.rb:51:in `require_from_bundler'
/var/lib/gems/2.5.0/gems/jekyll-3.8.3/exe/jekyll:11:in `<top (required)>'
/usr/local/bin/jekyll:23:in `load'
/usr/local/bin/jekyll:23:in `<top (required)>'
/usr/local/lib/site_ruby/2.5.0/bundler/cli/exec.rb:74:in `load'
/usr/local/lib/site_ruby/2.5.0/bundler/cli/exec.rb:74:in `kernel_load'
/usr/local/lib/site_ruby/2.5.0/bundler/cli/exec.rb:28:in `run'
/usr/local/lib/site_ruby/2.5.0/bundler/cli.rb:424:in `exec'
/usr/local/lib/site_ruby/2.5.0/bundler/vendor/thor/lib/thor/command.rb:27:in `run'
/usr/local/lib/site_ruby/2.5.0/bundler/vendor/thor/lib/thor/invocation.rb:126:in `invoke_command'
/usr/local/lib/site_ruby/2.5.0/bundler/vendor/thor/lib/thor.rb:387:in `dispatch'
/usr/local/lib/site_ruby/2.5.0/bundler/cli.rb:27:in `dispatch'
/usr/local/lib/site_ruby/2.5.0/bundler/vendor/thor/lib/thor/base.rb:466:in `start'
/usr/local/lib/site_ruby/2.5.0/bundler/cli.rb:18:in `start'
/usr/lib/ruby/gems/2.5.0/gems/bundler-1.16.2/exe/bundle:30:in `block in <top (required)>'
/usr/local/lib/site_ruby/2.5.0/bundler/friendly_errors.rb:124:in `with_friendly_errors'
/usr/lib/ruby/gems/2.5.0/gems/bundler-1.16.2/exe/bundle:22:in `<top (required)>'
/usr/local/bin/bundle:23:in `load'
/usr/local/bin/bundle:23:in `<main>'
Bundler Error Backtrace:

  /usr/local/lib/site_ruby/2.5.0/bundler/runtime.rb:84:in `rescue in block (2 levels) in require'
  /usr/local/lib/site_ruby/2.5.0/bundler/runtime.rb:80:in `block (2 levels) in require'
  /usr/local/lib/site_ruby/2.5.0/bundler/runtime.rb:76:in `each'
  /usr/local/lib/site_ruby/2.5.0/bundler/runtime.rb:76:in `block in require'
  /usr/local/lib/site_ruby/2.5.0/bundler/runtime.rb:65:in `each'
  /usr/local/lib/site_ruby/2.5.0/bundler/runtime.rb:65:in `require'
  /usr/local/lib/site_ruby/2.5.0/bundler.rb:114:in `require'
  /var/lib/gems/2.5.0/gems/jekyll-3.8.3/lib/jekyll/plugin_manager.rb:51:in `require_from_bundler'
  /var/lib/gems/2.5.0/gems/jekyll-3.8.3/exe/jekyll:11:in `<top (required)>'
  /usr/local/bin/jekyll:23:in `load'
  /usr/local/bin/jekyll:23:in `<top (required)>'

Any help is appreciated.

I did it! However I didn't use jekyll-katex plugin but jekyll-katek-block. I simply followed the instruction in its readme. Basically the only steps needed are:

1. Put katex_block.rb in _plugins folder

2. Store katex.min.js anywhere in your website. Default is /public/js/katex.min.js, otherwise you have to modify your _config.yml adding

   katex:
     path_to_js: "./your/path/to/katex/js"
   

3. (almost optional) Link katek.min.css and fonts.

katex.min.js, katex.min.css, and fonts can be downloaded from KaTeX GitHub page.

As I said my purpose was to run KaTeX with Jekyll and this method works. However, if someone else is able to make jekyll-katex works, since it was the original request, I'll mark it as accepted.