# HTMLMinifier
[](https://www.npmjs.com/package/html-minifier-terser)
[](https://github.com/terser/html-minifier-terser/actions?workflow=CI)
[HTMLMinifier](https://terser.org/html-minifier-terser/) is a highly **configurable**, **well-tested**, JavaScript-based HTML minifier.
## Installation
From NPM for use as a command line app:
```shell
npm install html-minifier-terser -g
```
From NPM for programmatic use:
```shell
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:**
```bash
html-minifier-terser --collapse-whitespace --remove-comments --minify-js true
```
### Node.js
```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](http://perfectionkills.com/experimenting-with-html-minifier) for all the gory details of [how it works](http://perfectionkills.com/experimenting-with-html-minifier#how_it_works), [description of each option](http://perfectionkills.com/experimenting-with-html-minifier#options), [testing results](http://perfectionkills.com/experimenting-with-html-minifier#field_testing) and [conclusions](http://perfectionkills.com/experimenting-with-html-minifier#cost_and_benefits).
Also see corresponding [Ruby wrapper](https://github.com/stereobooster/html_minifier), and for Node.js, [Grunt plugin](https://github.com/gruntjs/grunt-contrib-htmlmin), [Gulp plugin](https://github.com/pioug/gulp-html-minifier-terser), [Koa middleware wrapper](https://github.com/koajs/html-minifier) and [Express middleware wrapper](https://github.com/melonmanchan/express-minify-html).
For lint-like capabilities take a look at [HTMLLint](https://github.com/kangax/html-lint).
## Minification comparison
How does HTMLMinifier compare to other solutions — [HTML Minifier from Will Peavy](http://www.willpeavy.com/minifier/) (1st result in [Google search for "html minifier"](https://www.google.com/#q=html+minifier)) as well as [htmlcompressor.com](http://htmlcompressor.com) and [minimize](https://github.com/Swaagie/minimize)?
| Site | Original size *(KB)* | HTMLMinifier | minimize | Will Peavy | htmlcompressor.com |
| ---------------------------------------------------------------------------- |:--------------------:| ------------:| --------:| ----------:| ------------------:|
| [Google](https://www.google.com/) | 52 | **48** | 52 | 54 | n/a |
| [Stack Overflow](https://stackoverflow.com/) | 177 | **143** | 154 | 154 | n/a |
| [HTMLMinifier](https://github.com/kangax/html-minifier) | 252 | **171** | 230 | 250 | n/a |
| [Bootstrap CSS](https://getbootstrap.com/docs/3.3/css/) | 271 | **260** | 269 | 229 | n/a |
| [BBC](https://www.bbc.co.uk/) | 355 | **324** | 353 | 344 | n/a |
| [Amazon](https://www.amazon.co.uk/) | 466 | **430** | 456 | 474 | n/a |
| [Twitter](https://twitter.com/) | 469 | **394** | 462 | 513 | n/a |
| [Wikipedia](https://en.wikipedia.org/wiki/President_of_the_United_States) | 703 | **569** | 682 | 708 | n/a |
| [Eloquent Javascript](https://eloquentjavascript.net/1st_edition/print.html) | 870 | **815** | 840 | 864 | n/a |
| [NBC](https://www.nbc.com/) | 1701 | **1566** | 1689 | 1705 | n/a |
| [New York Times](https://www.nytimes.com/) | 1731 | **1583** | 1726 | 1680 | n/a |
| [ES draft](https://tc39.github.io/ecma262/) | 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](http://perfectionkills.com/experimenting-with-html-minifier#collapse_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](http://perfectionkills.com/experimenting-with-html-minifier#collapse_whitespace) | `false` |
| `conservativeCollapse` | Always collapse to 1 space (never remove it entirely). Must be used in conjunction with `collapseWhitespace=true` | `false` |
| `continueOnParseError` | [Handle parse errors](https://html.spec.whatwg.org/multipage/parsing.html#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](https://github.com/jakubpawlowicz/clean-css)) | `false` (could be `true`, `Object`, `Function(text, type)`) |
| `minifyJS` | Minify JavaScript in script elements and event attributes (uses [Terser](https://github.com/terser/terser)) | `false` (could be `true`, `Object`, `Function(text, inline)`) |
| `minifyURLs` | Minify URLs in various attributes (uses [relateurl](https://github.com/stevenvachon/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](http://perfectionkills.com/experimenting-with-html-minifier#remove_attribute_quotes) | `false` |
| `removeComments` | [Strip HTML comments](http://perfectionkills.com/experimenting-with-html-minifier#remove_comments) | `false` |
| `removeEmptyAttributes` | [Remove all attributes with whitespace-only values](http://perfectionkills.com/experimenting-with-html-minifier#remove_empty_or_blank_attributes) | `false` (could be `true`, `Function(attrName, tag)`) |
| `removeEmptyElements` | [Remove all elements with empty contents](http://perfectionkills.com/experimenting-with-html-minifier#remove_empty_elements) | `false` |
| `removeOptionalTags` | [Remove optional tags](http://perfectionkills.com/experimenting-with-html-minifier#remove_optional_tags) | `false` |
| `removeRedundantAttributes` | [Remove attributes when value matches default.](http://perfectionkills.com/experimenting-with-html-minifier#remove_redundant_attributes) | `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](#sorting-attributes--style-classes) | `false` |
| `sortClassName` | [Sort style classes by frequency](#sorting-attributes--style-classes) | `false` |
| `trimCustomFragments` | Trim white space around `ignoreCustomFragments`. | `false` |
| `useShortDoctype` | [Replaces the `doctype` with the short (HTML5) doctype](http://perfectionkills.com/experimenting-with-html-minifier#use_short_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:
```shell
cd benchmarks
npm install
npm run benchmark
```
## Running local server
```shell
npm run serve
```
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