html-minifier-next

# HTML Minifier Next [![npm version](https://img.shields.io/npm/v/html-minifier-next.svg)](https://www.npmjs.com/package/html-minifier-next) [![Build status](https://github.com/j9t/html-minifier-next/workflows/Tests/badge.svg)](https://github.com/j9t/html-minifier-next/actions) [![Socket](https://badge.socket.dev/npm/package/html-minifier-next)](https://socket.dev/npm/package/html-minifier-next) Your web page optimization precision tool: HTML Minifier Next (HMN) is a **super-configurable, well-tested, JavaScript-based HTML minifier** able to also handle in-document CSS, JavaScript, and SVG minification. The project was based on [HTML Minifier Terser (HMT)](https://github.com/terser/html-minifier-terser), which in turn had been based on [Juriy “kangax” Zaytsev’s HTML Minifier (HM)](https://github.com/kangax/html-minifier); as of 2025, both HTML Minifier Terser and HTML Minifier had been unmaintained for several years. HMN offers additional features and has been optimized for speed. While an independent project, it is still backwards-compatible with HMT and HM. ## Installation From npm for use as a command-line app: ```shell npm i -g html-minifier-next ``` Directly with npx: ```shell npx html-minifier-next --help ``` (For immediate, zero-config use in the current folder: `npx html-minifier-next --zero`) From npm for programmatic use: ```shell npm i html-minifier-next ``` ## General usage ### CLI Use `html-minifier-next --help` to check all available options: | Option | Description | Example | | --- | --- | --- | | `--zero`, `-z` | Minify all HTML files in the current folder and its subfolders in place (except node_modules), using comprehensive settings (standalone—flag is ignored when combined with other options) | `html-minifier-next --zero` | | `--input-dir <dir>`, `-I <dir>` | Specify an input directory | `--input-dir=src` | | `--ignore-dir <patterns>`, `-X <patterns>` | Exclude directories—relative to input directory—from processing (comma-separated, overrides config file setting) | `--ignore-dir=libs`, `--ignore-dir=libs,vendor,node_modules` | | `--output-dir <dir>`, `-O <dir>` | Specify an output directory | `--output-dir=dist` | | `--output <file>`, `-o <file>` | Specify output file (reads from file arguments or STDIN) | File to file: `html-minifier-next input.html -o output.html` Pipe to file: `cat input.html \| html-minifier-next -o output.html` File to STDOUT: `html-minifier-next input.html` | | `--file-ext <extensions>`, `-f <extensions>` | Specify file extension(s) to process (comma-separated, overrides config file setting); defaults to `html,htm,shtml,shtm`; use `*` for all files | `--file-ext=html,php`, `--file-ext='*'` | | `--preset <name>`, `-p <name>` | Use a preset configuration (conservative or comprehensive) | `--preset=conservative` | | `--config-file <file>`, `-c <file>` | Use a configuration file | `--config-file=html-minifier.json` | | `--verbose`, `-v` | Show detailed processing information (active options, file statistics) | `html-minifier-next --input-dir=src --output-dir=dist --verbose --collapse-whitespace` | | `--dry`, `-d` | Dry run: Process and report statistics without writing output | `html-minifier-next input.html --dry --collapse-whitespace` | ### Configuration file You can use a configuration file to specify options. The file can be either JSON format or a JavaScript module that exports the configuration object: **JSON configuration example:** ```json { "collapseWhitespace": true, "removeComments": true, "fileExt": "html,php", "ignoreDir": "libs,vendor" } ``` **JavaScript module configuration example:** ```javascript module.exports = { collapseWhitespace: true, removeComments: true, fileExt: "html,php", ignoreDir: ["libs", "vendor"] }; ``` ### Node.js ESM with Node.js ≥16.14: ```javascript import { minify } from 'html-minifier-next'; const result = await minify('foo', { removeAttributeQuotes: true, removeOptionalTags: true }); console.log(result); // “foo” ``` CommonJS: ```javascript const { minify } = require('html-minifier-next'); (async () => { const result = await minify('foo', { preset: 'comprehensive' }); console.log(result); // “foo” })(); ``` See [the original blog post](https://perfectionkills.com/experimenting-with-html-minifier/) for details of [how it works](https://perfectionkills.com/experimenting-with-html-minifier/#how_it_works), [descriptions of most options](https://perfectionkills.com/experimenting-with-html-minifier/#options), [testing results](https://perfectionkills.com/experimenting-with-html-minifier/#field_testing), and [conclusions](https://perfectionkills.com/experimenting-with-html-minifier/#cost_and_benefits). ## Presets HTML Minifier Next provides presets for common use cases. Presets are pre-configured option sets that can be used as a starting point: * `conservative`: Basic minification with whitespace collapsing, comment removal, and removal of select attributes. * `comprehensive`: More advanced minification for better file size reduction, including relevant conservative options plus attribute quote removal, optional tag removal, and more. To review the specific options set, [presets.js](https://github.com/j9t/html-minifier-next/blob/main/src/presets.js) lists them in an accessible manner. **Using presets:** ```shell # Via CLI flag html-minifier-next --preset conservative input.html # Via config file html-minifier-next --config-file=html-minifier.json input.html # where html-minifier.json contains: { "preset": "conservative" } # Override preset options html-minifier-next --preset conservative --remove-empty-attributes input.html ``` **Priority order:** Presets are applied first, then config file options, then CLI flags. This allows you to start with a preset and customize as needed. ## Options quick reference Most of the options are disabled by default. Experiment and find what works best for you and your project. Options can be used in config files (camelCase) or via CLI flags (kebab-case with `--` prefix). Options that default to `true` use `--no-` prefix in CLI to disable them. | Option (config/CLI) | Description | Default | | --- | --- | --- | | `cacheCSS` `--cache-css` | Set CSS minification cache size; higher values improve performance for batch processing | `500` | | `cacheJS` `--cache-js` | Set JavaScript minification cache size; higher values improve performance for batch processing | `500` | | `cacheSVG` `--cache-svg` | Set SVG minification cache size; higher values improve performance for batch processing | `500` | | `caseSensitive` `--case-sensitive` | Treat attributes in case-sensitive manner (useful for custom HTML elements) | `false` | | `collapseAttributeWhitespace` `--collapse-attribute-whitespace` | Trim and collapse whitespace characters within attribute values | `false` | | `collapseBooleanAttributes` `--collapse-boolean-attributes` | [Omit attribute values from boolean attributes](https://perfectionkills.com/experimenting-with-html-minifier/#collapse_boolean_attributes) | `false` | | `collapseInlineTagWhitespace` `--collapse-inline-tag-whitespace` | Collapse whitespace more aggressively between inline elements—use with `collapseWhitespace: true` | `false` | | `collapseWhitespace` `--collapse-whitespace` | [Collapse whitespace that contributes to text nodes in a document tree](https://perfectionkills.com/experimenting-with-html-minifier/#collapse_whitespace) | `false` | | `conservativeCollapse` `--conservative-collapse` | Always collapse to one space (never remove it entirely)—use with `collapseWhitespace: true` | `false` | | `continueOnMinifyError` `--no-continue-on-minify-error` | Continue on minification errors; when `false`, minification errors throw and abort processing | `true` | | `continueOnParseError` `--continue-on-parse-error` | [Handle parse errors](https://html.spec.whatwg.org/multipage/parsing.html#parse-errors) instead of aborting | `false` | | `customAttrAssign` `--custom-attr-assign` | Array of regexes that allow to support custom attribute assign expressions (e.g., `<div flex?="{{mode != cover}}"></div>`) | `[]` | | `customAttrCollapse` `--custom-attr-collapse` | Regex that specifies custom attribute to strip newlines from (e.g., `/ng-class/`) | `undefined` | | `customAttrSurround` `--custom-attr-surround` | Array of regexes that allow to support custom attribute surround expressions (e.g., `<input {{#if value}}checked="checked"{{/if}}>`) | `[]` | | `customEventAttributes` `--custom-event-attributes` | Array of regexes that allow to support custom event attributes for `minifyJS` (e.g., `ng-click`) | `[ /^on[a-z]{3,}$/ ]` | | `customFragmentQuantifierLimit` `--custom-fragment-quantifier-limit` | Set maximum quantifier limit for custom fragments to prevent ReDoS attacks | `200` | | `decodeEntities` `--decode-entities` | Use direct Unicode characters whenever possible | `false` | | `ignoreCustomComments` `--ignore-custom-comments` | Array of regexes that allow to ignore matching comments | `[ /^!/, /^\s*#/ ]` | | `ignoreCustomFragments` `--ignore-custom-fragments` | Array of regexes that allow to ignore certain fragments, when matched (e.g., `<?php … ?>`, `{{ … }}`, etc.) | `[ /<%[\s\S]*?%>/, /<\?[\s\S]*?\?>/ ]` | | `includeAutoGeneratedTags` `--include-auto-generated-tags` | Insert elements generated by HTML parser | `false` | | `inlineCustomElements` `--inline-custom-elements` | Array of names of custom elements which are inline, for whitespace handling | `[]` | | `keepClosingSlash` `--keep-closing-slash` | Keep the trailing slash on void elements | `false` | | `maxInputLength` `--max-input-length` | Maximum input length to prevent ReDoS attacks (disabled by default) | `undefined` | | `maxLineLength` `--max-line-length` | Specify a maximum line length; compressed output will be split by newlines at valid HTML split-points | `undefined` | | `mergeScripts` `--merge-scripts` | Merge consecutive inline `script` elements into one (only merges compatible scripts with same `type`, matching `async`/`defer`/`nomodule`/`nonce`) | `false` | | `minifyCSS` `--minify-css` | Minify CSS in `style` elements and attributes (uses [Lightning CSS](https://lightningcss.dev/)) | `false` (could be `true`, `Object`, `Function(text, type)`) | | `minifyJS` `--minify-js` | Minify JavaScript in `script` elements and event attributes (uses [Terser](https://terser.org/) or [SWC](https://swc.rs/)) | `false` (could be `true`, `Object`, `Function(text, inline)`) | | `minifySVG` `--minify-svg` | Minify SVG elements (uses [SVGO](https://svgo.dev/)) | `false` (could be `true`, `Object`) | | `minifyURLs` `--minify-urls` | Minify URLs in various attributes | `false` (could be `true`, `String`, `Object`, `Function(text)`) | | `noNewlinesBeforeTagClose` `--no-newlines-before-tag-close` | Never add a newline before a tag that closes an element | `false` | | `partialMarkup` `--partial-markup` | Treat input as a partial HTML fragment, preserving stray end tags (closing tags without opening tags) and preventing auto-closing of unclosed tags at end of input | `false` | | `preserveLineBreaks` `--preserve-line-breaks` | Always collapse to one line break (never remove it entirely) when whitespace between tags includes a line break—use with `collapseWhitespace: true` | `false` | | `preventAttributesEscaping` `--prevent-attributes-escaping` | Prevents the escaping of the values of attributes | `false` | | `processConditionalComments` `--process-conditional-comments` | Process contents of conditional comments through minifier | `false` | | `processScripts` `--process-scripts` | Array of strings corresponding to types of `script` elements to process through minifier (e.g., `text/ng-template`, `text/x-handlebars-template`, etc.) | `[]` | | `quoteCharacter` `--quote-character` | Type of quote to use for attribute values (`'` or `"`) | Auto-detected (uses the quote requiring less escaping; defaults to `"` when equal) | | `removeAttributeQuotes` `--remove-attribute-quotes` | [Remove quotes around attributes when possible](https://perfectionkills.com/experimenting-with-html-minifier/#remove_attribute_quotes) | `false` | | `removeComments` `--remove-comments` | [Strip HTML comments](https://perfectionkills.com/experimenting-with-html-minifier/#remove_comments) | `false` | | `removeEmptyAttributes` `--remove-empty-attributes` | [Remove all attributes with whitespace-only values](https://perfectionkills.com/experimenting-with-html-minifier/#remove_empty_or_blank_attributes) | `false` (could be `true`, `Function(attrName, tag)`) | | `removeEmptyElements` `--remove-empty-elements` | [Remove all elements with empty contents](https://perfectionkills.com/experimenting-with-html-minifier/#remove_empty_elements) | `false` | | `removeEmptyElementsExcept` `--remove-empty-elements-except` | Array of elements to preserve when `removeEmptyElements` is enabled; accepts simple tag names (e.g., `["td"]`) or HTML-like markup with attributes (e.g., `[""]`); supports double quotes, single quotes, and unquoted attribute values | `[]` | | `removeOptionalTags` `--remove-optional-tags` | [Remove optional tags](https://perfectionkills.com/experimenting-with-html-minifier/#remove_optional_tags) | `false` | | `removeRedundantAttributes` `--remove-redundant-attributes` | [Remove attributes when value matches default](https://meiert.com/blog/optional-html/#toc-attribute-values) | `false` | | `removeScriptTypeAttributes` `--remove-script-type-attributes` | Remove `type="text/javascript"` from `script` elements; other `type` attribute values are left intact | `false` | | `removeStyleLinkTypeAttributes` `--remove-style-link-type-attributes` | Remove `type="text/css"` from `style` and `link` elements; other `type` attribute values are left intact | `false` | | `removeTagWhitespace` `--remove-tag-whitespace` | Remove space between attributes whenever possible; **note that this will result in invalid HTML** | `false` | | `sortAttributes` `--sort-attributes` | [Sort attributes by frequency](#sorting-attributes-and-style-classes) | `false` | | `sortClassNames` `--sort-class-names` | [Sort style classes by frequency](#sorting-attributes-and-style-classes) | `false` | | `trimCustomFragments` `--trim-custom-fragments` | Trim whitespace around custom fragments (`ignoreCustomFragments`) | `false` | | `useShortDoctype` `--use-short-doctype` | [Replaces the doctype with the short HTML doctype](https://perfectionkills.com/experimenting-with-html-minifier/#use_short_doctype) | `false` | ### Sorting attributes and style classes Minifier options like `sortAttributes` and `sortClassNames` won’t impact the plain‑text size of the output. However, using these options for more consistent ordering improves the compression ratio for Gzip and Brotli used over HTTP. ### CSS minification When `minifyCSS` is set to `true`, HTML Minifier Next uses [Lightning CSS](https://lightningcss.dev/) to minify CSS in `style` elements and attributes. Lightning CSS provides excellent minification by default. You can pass Lightning CSS configuration options by providing an object: ```javascript const result = await minify(html, { minifyCSS: { targets: { // Browser targets for vendor prefix handling chrome: 95, firefox: 90, safari: 14 }, unusedSymbols: ['unused-class', 'old-animation'] } }); ``` Available Lightning CSS options when passed as an object: * `targets`: Browser targets for vendor prefix optimization (e.g., `{ chrome: 95, firefox: 90 }`). * `unusedSymbols`: Array of class names, IDs, keyframe names, and CSS variables to remove. * `errorRecovery`: Boolean to skip invalid rules instead of throwing errors. This is disabled by default in Lightning CSS, but enabled in HMN when the `continueOnMinifyError` option is set to `true` (the default). Explicitly setting `errorRecovery` in `minifyCSS` options will override this automatic behavior. * `sourceMap`: Boolean to generate source maps. For advanced usage, you can also pass a function: ```javascript const result = await minify(html, { minifyCSS: function(text, type) { // `text`: CSS string to minify // `type`: `inline` for style attributes, `media` for media queries, `undefined` for `<style>` elements return yourCustomMinifier(text); } }); ``` ### JavaScript minification When `minifyJS` is set to `true`, HTML Minifier Next uses [Terser](https://terser.org/) by default to minify JavaScript in `<script>` elements and event attributes. You can choose between different JS minifiers using the `engine` field: ```javascript const result = await minify(html, { minifyJS: { engine: 'swc', // Use SWC for faster minification // SWC-specific options here } }); ``` **Available engines:** * `terser` (default): The standard JavaScript minifier with excellent compression * [`swc`](https://swc.rs/): Rust-based minifier that’s significantly faster than Terser (requires separate installation) **To use SWC**, install it as a dependency: ```shell npm i @swc/core ``` (Build-only users may want to install it as a dev dependency: `npm i -D @swc/core`.) **Important:** Inline event handlers (e.g., `onclick="return false"`) always use Terser regardless of the `engine` setting, as SWC doesn’t support bare return statements. This is handled automatically—you don’t need to do anything special. You can pass engine-specific configuration options: ```javascript // Using Terser with custom options const result = await minify(html, { minifyJS: { compress: { drop_console: true // Remove console.log statements } } }); // Using SWC for faster minification const result = await minify(html, { minifyJS: { engine: 'swc' } }); ``` For advanced usage, you can also pass a function: ```javascript const result = await minify(html, { minifyJS: function(text, inline) { // `text`: JavaScript string to minify // `inline`: `true` for event handlers (e.g., `onclick`), `false` for `<script>` elements return yourCustomMinifier(text); } }); ``` ### SVG minification When `minifySVG` is set to `true`, HTML Minifier Next uses [SVGO](https://svgo.dev/) to optimize inline SVG elements. Complete `<svg>` subtrees are extracted and processed as a block, enabling deep structural optimization: ```javascript const result = await minify(html, { minifySVG: true // Enable with SVGO defaults }); ``` You can pass custom SVGO options: ```javascript const result = await minify(html, { minifySVG: { plugins: [{ name: 'preset-default', params: { overrides: { convertShapeToPath: false // Keep original shapes } } }] } }); ``` **Important:** * SVG minification only applies within `<svg>` elements * Case sensitivity and self-closing slashes are automatically preserved in SVG (regardless of global settings) * For maximum compression, use `minifySVG` together with `collapseWhitespace` and other options ### CSS, JavaScript, and SVG cache configuration HTML Minifier Next uses in-memory caches to improve performance when processing multiple files or repeated content. The cache sizes can be configured for optimal performance based on your use case: ```javascript const result = await minify(html, { minifyCSS: true, minifyJS: true, minifySVG: true, // Configure cache sizes (in number of entries) cacheCSS: 750, // CSS cache size, default: 500 cacheJS: 250, // JS cache size, default: 500 cacheSVG: 100 // SVG cache size, default: 500 }); ``` **Via CLI flags:** ```shell html-minifier-next --minify-css --cache-css 750 --minify-js --cache-js 250 --minify-svg --cache-svg 100 input.html ``` **Via environment variables:** ```shell export HMN_CACHE_CSS=750 export HMN_CACHE_JS=250 export HMN_CACHE_SVG=100 html-minifier-next --minify-css --minify-js --minify-svg input.html ``` **Configuration file:** ```json { "minifyCSS": true, "cacheCSS": 750, "minifyJS": true, "cacheJS": 250, "minifySVG": true, "cacheSVG": 100 } ``` **When to adjust cache sizes:** * Single file processing: Default `500` is sufficient * Batch processing: Increase to `1000` or higher for better cache hit rates * Memory-constrained environments: Reduce to `200`–`300` to save memory * Hundreds/thousands of files: Increase to `1000`–`2000` for optimal performance **Important:** * Cache locking: Caches are created on the first `minify()` call and persist for the process lifetime. Cache sizes are locked after first initialization—subsequent calls reuse the same caches even if different `cacheCSS`, `cacheJS`, or `cacheSVG` options are provided. The first call’s options determine the cache sizes. * Zero values: Explicit `0` values are coerced to `1` (minimum functional cache size) to avoid immediate eviction. If you want to minimize memory usage, use a small number like `10` or `50` instead of `0`. The caches persist across multiple `minify()` calls, making them particularly effective when processing many files in a batch operation. ## Minification comparison Please see [**the Minifier Benchmarks project**](https://github.com/j9t/minifier-benchmarks) for details on how HMN compares to other minifiers. ## Examples ### CLI **Sample command line:** ```shell html-minifier-next --collapse-whitespace --remove-comments --minify-js --input-dir=. --output-dir=example ``` Example using npx: ```shell npx html-minifier-next --input-dir=test --preset comprehensive --output-dir example ``` **Process specific files and directories:** ```shell # Process default extensions (html, htm, shtml, shtm) html-minifier-next --collapse-whitespace --input-dir=src --output-dir=dist # Process only specific extensions html-minifier-next --collapse-whitespace --input-dir=src --output-dir=dist --file-ext=html,php # Using configuration file that sets `fileExt` (e.g., `"fileExt": "html,php"`) html-minifier-next --config-file=html-minifier.json --input-dir=src --output-dir=dist # Process all files (explicit wildcard) html-minifier-next --collapse-whitespace --input-dir=src --output-dir=dist --file-ext='*' ``` **Exclude directories from processing:** ```shell # Ignore a single directory html-minifier-next --collapse-whitespace --input-dir=src --output-dir=dist --ignore-dir=libs # Ignore multiple directories html-minifier-next --collapse-whitespace --input-dir=src --output-dir=dist --ignore-dir=libs,vendor,node_modules # Ignore by relative path (only ignores src/static/libs, not other “libs” directories) html-minifier-next --collapse-whitespace --input-dir=src --output-dir=dist --ignore-dir=static/libs ``` **Dry run mode (preview outcome without writing files):** ```shell # Preview with output file html-minifier-next input.html -o output.html --dry --collapse-whitespace # Preview directory processing with statistics per file and total html-minifier-next --input-dir=src --output-dir=dist --dry --collapse-whitespace # Output: [DRY RUN] Would process directory: src → dist # index.html: 1,234 → 892 bytes (-342, 27.7%) # about.html: 2,100 → 1,654 bytes (-446, 21.2%) # --- # Total: 3,334 → 2,546 bytes (-788, 23.6%) ``` **Verbose mode (show detailed processing information):** ```shell # Show processing details while minifying html-minifier-next --input-dir=src --output-dir=dist --verbose --collapse-whitespace # Output: CLI options: collapseWhitespace # ✓ src/index.html: 1,234 → 892 bytes (-342, 27.7%) # ✓ src/about.html: 2,100 → 1,654 bytes (-446, 21.2%) # --- # Total: 3,334 → 2,546 bytes (-788, 23.6%) # `--dry` automatically enables verbose output html-minifier-next --input-dir=src --output-dir=dist --dry --collapse-whitespace ``` ## Special cases ### Ignoring chunks of markup If you have chunks of markup you would like preserved, you can wrap them with ``. ### Minifying JSON content JSON script types are minified automatically without configuration, including `application/json`, `application/ld+json`, `application/manifest+json`, `application/vnd.geo+json`, `application/problem+json`, `application/merge-patch+json`, `application/json-patch+json`, `importmap`, and `speculationrules`. Malformed JSON is preserved by default (with `continueOnMinifyError: true`). Note: The `processScripts` option is only for script types containing HTML templates (e.g., `text/ng-template`, `text/x-handlebars-template`), not for JSON. ### Preserving SVG and MathML elements SVG and MathML elements are automatically recognized as foreign elements, and when they are minified, both case-sensitivity and self-closing slashes are preserved, regardless of the minification settings used for the rest of the file. This ensures valid output for these namespaced elements. ### Working with invalid or partial markup By default, HTML Minifier Next parses markup into a complete tree structure, then modifies it (removing anything that was specified for removal, ignoring anything that was specified to be ignored, etc.), then creates markup from that tree and returns it. _Input markup (e.g., `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., `foo`)_ For partial HTML fragments (such as template includes, SSI fragments, or closing tags without opening tags), use the `partialMarkup: true` option. This preserves stray end tags (closing tags without corresponding opening tags) and prevents auto-closing of unclosed tags at the end of input. Note that normal HTML auto-closing rules still apply during parsing—for example, a closing parent tag will still auto-close its unclosed child elements. To validate complete HTML markup, use [the W3C validator](https://validator.w3.org/) or one of [several validator packages](https://meiert.com/blog/html-validator-packages/). ## Security ### ReDoS protection This minifier includes protection against regular expression denial of service (ReDoS) attacks: * Custom fragment quantifier limits: The `customFragmentQuantifierLimit` option (default: 200) prevents exponential backtracking by replacing unlimited quantifiers (`*`, `+`) with bounded ones in regular expressions. * Input length limits: The `maxInputLength` option allows you to set a maximum input size to prevent processing of excessively large inputs that could cause performance issues. * Enhanced pattern detection: The minifier detects and warns about various ReDoS-prone patterns including nested quantifiers, alternation with quantifiers, and multiple unlimited quantifiers. **Important:** When using custom `ignoreCustomFragments`, ensure your regular expressions don’t contain unlimited quantifiers (`*`, `+`) without bounds, as these can lead to ReDoS vulnerabilities. #### Custom fragment examples **Safe patterns** (recommended): ```javascript ignoreCustomFragments: [ /<%[\s\S]{0,1000}?%>/, // JSP/ASP with explicit bounds /<\?php[\s\S]{0,5000}?\?>/, // PHP with bounds /\{\{[^}]{0,500}\}\}/ // Handlebars without nested braces ] ``` **Potentially unsafe patterns** (will trigger warnings): ```javascript ignoreCustomFragments: [ /<%[\s\S]*?%>/, // Unlimited quantifiers //, // Could cause issues with very long comments /\{\{.*?\}\}/, // Nested unlimited quantifiers /(script|style)[\s\S]*?/ // Multiple unlimited quantifiers ] ``` **Template engine configurations:** ```javascript // Handlebars/Mustache ignoreCustomFragments: [/\{\{[\s\S]{0,1000}?\}\}/] // Liquid (Jekyll) ignoreCustomFragments: [/\{%[\s\S]{0,500}?%\}/, /\{\{[\s\S]{0,500}?\}\}/] // Angular ignoreCustomFragments: [/\{\{[\s\S]{0,500}?\}\}/] // Vue.js ignoreCustomFragments: [/\{\{[\s\S]{0,500}?\}\}/] ``` **Important:** When using custom `ignoreCustomFragments`, the minifier automatically applies bounded quantifiers to prevent ReDoS attacks, but you can also write safer patterns yourself using explicit bounds. ##### Escaping patterns in different contexts The escaping requirements for `ignoreCustomFragments` patterns differ depending on how you’re using HMN: **Config file (JSON):** ```json { "ignoreCustomFragments": ["\\{%[\\s\\S]{0,1000}?%\\}", "\\{\\{[\\s\\S]{0,500}?\\}\\}"] } ``` **Programmatic (JavaScript/Node.js):** ```javascript ignoreCustomFragments: [/\{%[\s\S]{0,1000}?%\}/, /\{\{[\s\S]{0,500}?\}\}/] ``` **CLI (via config file—recommended):** ```shell html-minifier-next --config-file=config.json input.html ``` **CLI (inline—not recommended due to complex escaping):** ```shell html-minifier-next --ignore-custom-fragments '[\\\"\\\\{%[\\\\s\\\\S]{0,1000}?%\\\\}\\\"]' input.html ``` For CLI usage, using a config file is strongly recommended to avoid complex shell and JSON escaping. **[Web demo:](https://j9t.github.io/html-minifier-next/)** ``` \{%[\s\S]{0,1000}?%\} \{\{[\s\S]{0,500}?\}\} ``` ## Running HTML Minifier Next locally ### Local server ```shell npm run serve ``` ### Regression tests ```shell cd backtest; npm i; npm run backtest ``` The backtest tool tracks minification performance across Git history. Results are saved in the backtest folder as CSV and JSON files. Parameters: * No argument: Tests last 50 commits (default) * `COUNT`: Tests last `COUNT` commits (e.g., `npm run backtest 100`) * `COUNT/STEP`: Tests last `COUNT` commits, sampling every `STEP`th commit (e.g., `npm run backtest 500/10` tests 50 commits) ## Acknowledgements With many thanks to all the previous authors of HTML Minifier, especially [Juriy “kangax” Zaytsev](https://github.com/kangax), and to everyone who helped make this new edition better, particularly [Daniel Ruf](https://github.com/DanielRuf) and [Jonas Geiler](https://github.com/jonasgeiler).