HTML Compressor in Shopify Liquid

compress.liquid

{% comment %}

	Input

{% endcomment %}{% capture _content %}{{ content }}{% endcapture %}{% comment %}

	Remove redundant closing tags

{% endcomment %}{% assign _endings = "html head body li dt dd p rt rp optgroup option colgroup caption thead tbody tfoot tr td th" | split: " " %}{% for _element in _endings %}
	{% capture _end %}</{{ _element }}>{% endcapture %}
	{% assign _content = _content | remove: _end %}
{% endfor %}{% comment %}

	Create a variable to match newlines

{% endcomment %}{% capture nl %}
{% endcapture %}{% comment %}

	Prepare inline <script>'s for compression
		- We have to ensure a space after every </script> otherwise Liquid won't match, and blow up everything if two elements comes straight after eachother: <script></script><div></div>

{% endcomment %}{% assign _content = _content | replace: '</script>', '</script><!-- [SPACE] -->' | replace: '<!-- [SPACE] -->', " " %}{% assign _script_befores = _content | split: "<script" %}{% assign _content = "" %}{% for _script_before in _script_befores %}
	{% assign _scripts = _script_before | split: "</script>" %}
    {% case _scripts.size %}
    {% when 2 %}
		{% assign _script = _scripts.first |

			replace: "// //", "/*[COMMENT]*/ " |
			replace: "//	//", "/*[COMMENT]*/ " |
			replace: "// ", "/*[COMMENT]*/ " |
			replace: " //", "/*[COMMENT]*/ " |
			replace: "  	//", "/*[COMMENT]*/ " |
			replace: "//	", "/*[COMMENT]*/ " |
			replace: "//<![CDATA[", "/*[COMMENT]*/ " |
			replace: "//]]>", "/*[COMMENT]*/ " |

		%}

		{% assign _script_comment_befores = _script | split: "/*[COMMENT]*/ " %}{% for _script_comment_before in _script_comment_befores %}
			{% assign _script_comment_content = _script_comment_before | split: nl | first %}
			{% if _script_comment_content %}
				{% capture _script_comment %}{{ "/*[COMMENT]*/ " }}{{ _script_comment_content }}{{ nl }}{% endcapture %}
				{% assign _script = _script | remove: _script_comment  %}
			{% endif %}
		{% endfor %}
		{% assign _script_comment_befores = _script | split: "/*" %}{% for _script_comment_before in _script_comment_befores %}
			{% assign _script_comment_content = _script_comment_before | split: "*/" | first %}
			{% if _script_comment_content %}
				{% capture _script_comment %}{{ "/*" }}{{ _script_comment_content }}{{ "*/" }}{% endcapture %}
				{% assign _script = _script | remove: _script_comment  %}
			{% endif %}
		{% endfor %}

		{% capture _content %}{{ _content }}<script {{ _script }}</script>{{ _scripts.last }}{% endcapture %}
    {% when 1 %}
		{% capture _content %}{{ _content }}{{ _scripts.last }}{% endcapture %}
    {% endcase %}
{% endfor %}{% comment %}

	Cleanup
		- There is an 'missing semicolon' issue with Shopify's Enhanced Ecommerce for Google Analytics, which gets corrected here as well.
		- There is an 'missing semicolon' issue with Shopify's inline Admin Panel script, which gets corrected here as well.

{% endcomment %}{% assign _content = _content | replace: '<script >', '<script>' | replace: '<script  ', '<script ' | replace: 'analytics.onload = onload', ';analytics.onload = onload' | replace: 'analytics.async = true;', ';analytics.async = true;' | replace: 'if (window.addEventListener){ addEventListener("message", ', ';if (window.addEventListener){ addEventListener("message", ' %}{% comment %}

	Compress whitespace outside of <pre>
		- We have to ensure a space after every </pre> otherwise Liquid won't match, and blow up everything if two elements comes straight after eachother: <pre></pre><div></div>

{% endcomment %}{% assign _content = _content | replace: '</pre>', '</pre><!-- [SPACE] -->' | replace: '<!-- [SPACE] -->', " " %}{% assign _pre_befores = _content | split: "<pre" %}{% assign _content = "" %}{% for _pre_before in _pre_befores %}
  {% assign _pres = _pre_before | split: "</pre>" %}
    {% case _pres.size %}
    {% when 2 %}
      {% capture _content %}{{ _content }}<pre{{ _pres.first }}</pre>{{ _pres.last | split: " " | join: " " }}{% endcapture %}
    {% when 1 %}
      {% capture _content %}{{ _content }}{{ _pres.last | split: " " | join: " " }}{% endcapture %}
    {% endcase %}
{% endfor %}{% comment %}

	Remove html comments
		- Matching just "<!--" and "-->" will whipe out IE Conditional Comments, which you probably don't want

{% endcomment %}{% assign _comment_befores = _content | split: "<!-- " %}{% for _comment_before in _comment_befores %}
	{% assign _comment_content = _comment_before | split: " -->" | first %}
	{% if _comment_content %}
		{% capture _comment %}{{ "<!-- " }}{{ _comment_content }}{{ " -->" }}{% endcapture %}
		{% assign _content = _content | remove: _comment %}
	{% endif %}
{% endfor %}{% comment %}

	Clip whitespace around elements

{% endcomment %}{% assign _clippings = "html head title base link meta style body article section nav aside h1 h2 h3 h4 h5 h6 hgroup header footer address p hr blockquote ol ul li dl dt dd figure figcaption main div table caption colgroup col tbody thead tfoot tr td th option img script" | split: " " %}{% for _element in _clippings %}
	{% assign _edges = " <e;<e; </e>;</e>;</e> ;</e>" | replace: "e", _element | split: ";" %}
	{% assign _content = _content | replace: _edges[0], _edges[1] | replace: _edges[2], _edges[3] | replace: _edges[4], _edges[5] %}
{% endfor %}{% comment %}

	Output

{% endcomment %}{{ _content }}

You can use it like this:
Create a snippit name 'compress'
{%- capture minified -%}
<!doctype html>
<!--all content--->
</html>
{%- endcapture -%}
{%- include 'compress', content: minified -%}