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HTMLMinifier

NPM version Build Status Dependency Status

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

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, 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 46 42 46 48 46
HTMLMinifier 125 98 111 117 111
Twitter 207 165 200 224 200
Stack Overflow 253 195 207 215 204
Bootstrap CSS 271 260 269 228 269
BBC 298 239 290 291 280
Amazon 422 316 412 425 n/a
NBC 553 530 552 553 534
Wikipedia 565 461 548 569 548
New York Times 678 606 675 670 n/a
Eloquent Javascript 870 815 840 864 n/a
ES6 table 5911 5051 5595 n/a n/a
ES draft 6126 5495 5664 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 [ /^!/ ]
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 UglifyJS) false (could be true, Object, Function(text, inline))
minifyURLs Minify URLs in various attributes (uses relateurl) false (could be String, Object, Function(text))
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 -->.

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.

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

Note that almost all options are disabled by default. For command line usage please see html-minifier --help for a list of available options. Experiment and find what works best for you and your project.

  • Sample command line: html-minifier --collapse-whitespace --remove-comments --remove-optional-tags --remove-redundant-attributes --remove-script-type-attributes --remove-tag-whitespace --use-short-doctype --minify-css true --minify-js true

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