HTMLMinifier

HTMLMinifier is a highly configurable, well-tested, JavaScript-based HTML minifier.

Installation

From NPM for use as a command line app:

npm install html-minifier-terser -g

From NPM for programmatic use:

npm install html-minifier-terser

Usage

Note that almost all options are disabled by default. Experiment and find what works best for you and your project.

For command line usage please see html-minifier-terser --help for a list of available options.

Sample command line:

html-minifier-terser --collapse-whitespace --remove-comments --minify-js true

Node.js

const { minify } = require('html-minifier-terser');

const result = await minify('<p title="blah" id="moo">foo</p>', {
  removeAttributeQuotes: true,
});
result; // '<p title=blah id=moo>foo</p>'

See corresponding blog post for all the gory details of how it works, description of each option, testing results and conclusions.

Also see corresponding Ruby wrapper, and for Node.js, Grunt plugin, Gulp plugin, Koa middleware wrapper and Express middleware wrapper.

For lint-like capabilities take a look at HTMLLint.

Minification comparison

How does HTMLMinifier compare to other solutions — HTML Minifier from Will Peavy (1st result in Google search for "html minifier") as well as htmlcompressor.com and minimize?

Site	Original size (KB)	HTMLMinifier	minimize	Will Peavy	htmlcompressor.com
Google	52	48	52	54	n/a
Stack Overflow	177	143	154	154	n/a
HTMLMinifier	252	171	230	250	n/a
Bootstrap CSS	271	260	269	229	n/a
BBC	355	324	353	344	n/a
Amazon	466	430	456	474	n/a
Twitter	469	394	462	513	n/a
Wikipedia	703	569	682	708	n/a
Eloquent Javascript	870	815	840	864	n/a
NBC	1701	1566	1689	1705	n/a
New York Times	1731	1583	1726	1680	n/a
ES draft	6296	5538	5733	n/a	n/a

Options Quick Reference

Most of the options are disabled by default.

Option	Description	Default
caseSensitive	Treat attributes in case sensitive manner (useful for custom HTML tags)	false
collapseBooleanAttributes	Omit attribute values from boolean attributes	false
collapseInlineTagWhitespace	Don't leave any spaces between display:inline; elements when collapsing. Must be used in conjunction with collapseWhitespace=true	false
collapseWhitespace	Collapse white space that contributes to text nodes in a document tree	false
conservativeCollapse	Always collapse to 1 space (never remove it entirely). Must be used in conjunction with collapseWhitespace=true	false
continueOnParseError	Handle parse errors instead of aborting.	false
customAttrAssign	Arrays of regex'es that allow to support custom attribute assign expressions (e.g. '<div flex?="{{mode != cover}}"></div>')	[ ]
customAttrCollapse	Regex that specifies custom attribute to strip newlines from (e.g. /ng-class/)
customAttrSurround	Arrays of regex'es that allow to support custom attribute surround expressions (e.g. <input {{#if value}}checked="checked"{{/if}}>)	[ ]
customEventAttributes	Arrays of regex'es that allow to support custom event attributes for minifyJS (e.g. ng-click)	[ /^on[a-z]{3,}$/ ]
decodeEntities	Use direct Unicode characters whenever possible	false
html5	Parse input according to HTML5 specifications	true
ignoreCustomComments	Array of regex'es that allow to ignore certain comments, when matched	[ /^!/, /^\s*#/ ]
ignoreCustomFragments	Array of regex'es that allow to ignore certain fragments, when matched (e.g. <?php ... ?>, {{ ... }}, etc.)	[ /<%[\s\S]*?%>/, /<\?[\s\S]*?\?>/ ]
includeAutoGeneratedTags	Insert tags generated by HTML parser	true
keepClosingSlash	Keep the trailing slash on singleton elements	false
maxLineLength	Specify a maximum line length. Compressed output will be split by newlines at valid HTML split-points
minifyCSS	Minify CSS in style elements and style attributes (uses clean-css)	false (could be true, Object, Function(text, type))
minifyJS	Minify JavaScript in script elements and event attributes (uses Terser)	false (could be true, Object, Function(text, inline))
minifyURLs	Minify URLs in various attributes (uses relateurl)	false (could be String, Object, Function(text))
noNewlinesBeforeTagClose	Never add a newline before a tag that closes an element	false
preserveLineBreaks	Always collapse to 1 line break (never remove it entirely) when whitespace between tags include a line break. Must be used in conjunction with collapseWhitespace=true	false
preventAttributesEscaping	Prevents the escaping of the values of attributes	false
processConditionalComments	Process contents of conditional comments through minifier	false
processScripts	Array of strings corresponding to types of script elements to process through minifier (e.g. text/ng-template, text/x-handlebars-template, etc.)	[ ]
quoteCharacter	Type of quote to use for attribute values (' or ")
removeAttributeQuotes	Remove quotes around attributes when possible	false
removeComments	Strip HTML comments	false
removeEmptyAttributes	Remove all attributes with whitespace-only values	false (could be true, Function(attrName, tag))
removeEmptyElements	Remove all elements with empty contents	false
removeOptionalTags	Remove optional tags	false
removeRedundantAttributes	Remove attributes when value matches default.	false
removeScriptTypeAttributes	Remove type="text/javascript" from script tags. Other type attribute values are left intact	false
removeStyleLinkTypeAttributes	Remove type="text/css" from style and link tags. Other type attribute values are left intact	false
removeTagWhitespace	Remove space between attributes whenever possible. Note that this will result in invalid HTML!	false
sortAttributes	Sort attributes by frequency	false
sortClassName	Sort style classes by frequency	false
trimCustomFragments	Trim white space around ignoreCustomFragments.	false
useShortDoctype	Replaces the doctype with the short (HTML5) doctype	false

Sorting attributes / style classes

Minifier options like sortAttributes and sortClassName won't impact the plain-text size of the output. However, they form long repetitive chains of characters that should improve compression ratio of gzip used in HTTP compression.

Special cases

Ignoring chunks of markup

If you have chunks of markup you would like preserved, you can wrap them <!-- htmlmin:ignore -->.

Minifying JSON-LD

You can minify script tags with JSON-LD by setting the option { processScripts: ['application/ld+json'] }. Note that this minification is very rudimentary, it is mainly useful for removing newlines and excessive whitespace.

Preserving SVG tags

SVG tags are automatically recognized, and when they are minified, both case-sensitivity and closing-slashes are preserved, regardless of the minification settings used for the rest of the file.

Working with invalid markup

HTMLMinifier can't work with invalid or partial chunks of markup. This is because it parses markup into a tree structure, then modifies it (removing anything that was specified for removal, ignoring anything that was specified to be ignored, etc.), then it creates a markup out of that tree and returns it.

Input markup (e.g. <p id="">foo)

↓

Internal representation of markup in a form of tree (e.g. { tag: "p", attr: "id", children: ["foo"] })

↓

Transformation of internal representation (e.g. removal of id attribute)

↓

Output of resulting markup (e.g. <p>foo</p>)

HTMLMinifier can't know that original markup was only half of the tree; it does its best to try to parse it as a full tree and it loses information about tree being malformed or partial in the beginning. As a result, it can't create a partial/malformed tree at the time of the output.

Running benchmarks

Benchmarks for minified HTML:

cd benchmarks
npm install
npm run benchmark

Running local server

npm run serve