html-minifier: An HTML repository from kt3k

HTMLMinifier is a highly configurable, well-tested, JavaScript-based HTML minifier, with lint-like capabilities.

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

Test suite is available online.

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

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
HTMLMinifier page	49	37	42	44	43
NBC	91	74	84	86	85
ES6 table	118	80	93	95	94
New York Times	131	101	122	125	120
Google	133	128	132	135	131
MSN	157	130	138	145	138
Stackoverflow	200	159	165	174	166
Amazon	246	204	234	230	219
Wikipedia	401	367	388	400	n/a
Eloquent Javascript	870	827	840	864	n/a
ES6 draft	3678	2990	3079	3204	n/a

Options Quick Reference

Option	Description	Default
`removeComments`	Strip HTML comments	`false`
`removeCommentsFromCDATA`	Strip HTML comments from scripts and styles	`false`
`removeCDATASectionsFromCDATA`	Remove CDATA sections from script and style elements	`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`
`collapseInlineTagWhitespace`	Don't leave any spaces between `display:inline;` elements when collapsing. Must be used in conjunction with `collapseWhitespace=true`	`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`
`collapseBooleanAttributes`	Omit attribute values from boolean attributes	`false`
`removeTagWhitespace`	Remove space between attributes whenever possible.	`false`
`removeAttributeQuotes`	Remove quotes around attributes when possible.	`false`
`removeRedundantAttributes`	Remove attributes when value matches default.	`false`
`preventAttributesEscaping`	Prevents the escaping of the values of attributes.	`false`
`useShortDoctype`	Replaces the doctype with the short (HTML5) doctype	`false`
`removeEmptyAttributes`	Remove all attributes with whitespace-only values	`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`
`removeOptionalTags`	Remove unrequired tags	`false`
`removeEmptyElements`	Remove all elements with empty contents	`false`
`lint`	Toggle linting	`false`
`keepClosingSlash`	Keep the trailing slash on singleton elements	`false`
`caseSensitive`	Treat attributes in case sensitive manner (useful for custom HTML tags.)	`false`
`minifyJS`	Minify Javascript in script elements and event attributes (uses UglifyJS)	`false` (could be `true`, `false`, `Object` (options))
`minifyCSS`	Minify CSS in style elements and style attributes (uses clean-css)	`false` (could be `true`, `false`, `Object` (options))
`minifyURLs`	Minify URLs in various attributes (uses relateurl)	`false` (could be `Object` (options))
`ignoreCustomComments`	Array of regex'es that allow to ignore certain comments, when matched	`[ ]`
`ignoreCustomFragments`	Array of regex'es that allow to ignore certain fragments, when matched (e.g. `<?php ... ?>`, `{{ ... }}`, etc.)	`[ /<%[\s\S]?%>/, /<\?[\s\S]?\?>/ ]`
`processScripts`	Array of strings corresponding to types of script elements to process through minifier (e.g. `text/ng-template`, `text/x-handlebars-template`, etc.)	`[ ]`
`maxLineLength`	Specify a maximum line length. Compressed output will be split by newlines at valid HTML split-points.
`customEventAttributes`	Arrays of regex'es that allow to support custom event attributes for `minifyJS` (e.g. `ng-click`)	`[ /^on[a-z]{3,}$/ ]`
`customAttrAssign`	Arrays of regex'es that allow to support custom attribute assign expressions (e.g. `'<div flex?="{{mode != cover}}"></div>'`)	`[ ]`
`customAttrSurround`	Arrays of regex'es that allow to support custom attribute surround expressions (e.g. `<input {{#if value}}checked="checked"{{/if}}>`)	`[ ]`
`customAttrCollapse`	Regex that specifies custom attribute to strip newlines from (e.g. `/ng\-class/`)
`quoteCharacter`	Type of quote to use for attribute values (' or ")

Special cases

Ignoring chunks of markup

If you have chunks of markup you would like preserved, you can wrap them .

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 ingored, 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.

Installation Instructions

From NPM for use as a command line app:

npm install html-minifier -g

From NPM for programmatic use:

npm install html-minifier

From Git:

git clone git://github.com/kangax/html-minifier.git
cd html-minifier
npm link .

Usage

For command line usage please see html-minifier --help

Node.js

var minify = require('html-minifier').minify;
var result = minify('<p title="blah" id="moo">foo</p>', {
  removeAttributeQuotes: true
});
result; // '<p title=blah id=moo>foo</p>'

Running benchmarks

Benchmarks for minified HTML:

node benchmark.js

kt3k/html-minifier