@literals/html-css-minifier

Minify HTML markup inside JavaScript template literal strings.

Why?

Template literals are often used in JavaScript to write HTML and CSS markup (ex. lit-html). This library allows a developer to minify markup that is normally ignored by JavaScript minifiers.

Usage

[!IMPORTANT]
All @literals/* packages are published as ESM-only!

import { minifyHTMLLiterals } from '@literals/html-css-minifier';

const result = await minifyHTMLLiterals(
  `function render(title, items) {
    return html\`
      <style>
        .heading {
          color: blue;
        }
      </style>
      <h1 class="heading">\${title}</h1>
      <ul>
        \${items.map(item => {
          return getHTML()\`
            <li>\${item}</li>
          \`;
        })}
      </ul>
    \`;
  }`,
  {
    fileName: 'render.js',
  },
);

console.log(result?.code);
//  function render(title, items) {
//    return html`<style>.heading{color:#00f}</style><h1 class=heading>${title}</h1><ul>${items.map(item => {
//          return getHTML()`<li>${item}</li>`;
//        })}</ul>`;
//  }

console.log(result?.map);
// {
//   "version": 3,
//   "file": "render.js.map",
//   "sources": ["render.js"],
//   "sourcesContent": [null],
//   "names": [],
//   "mappings": "AAAA;gBACgB,qDAMU,QAAQ,SAE1B;2BACmB,IACX,OAAO,KACb;WACC,KAEP;"
// }

ES5 Transpiling Warning

Be sure to minify template literals before transpiling to ES5. Otherwise, the API will not be able to find any template literal (`${}`) strings.

Supported Source Syntax

• JavaScript
• TypeScript

Options

Basic

The following options are common to typical use cases.

Property	Type	Default	Description
fileName	string		Required. The name of the file, used for syntax parsing and source maps.
minifyOptions?	html-minifier options	defaultMinifyOptions	Defaults to production-ready minification.
minifyOptions?.minifyCSS?	clean-css options	defaultMinifyCSSOptions	Uses clean-css defaults.
shouldMinify?	function	defaultShouldMinify	A function that determines whether or not an HTML template should be minified. Defaults to minify all tagged templates whose tag name contains "html" (case insensitive).
shouldMinifyCSS?	function	defaultShouldMinifyCSS	A function that determines whether or not a CSS template should be minified. Defaults to minify all tagged templates whose tag name contains "css" (case insensitive).

Advanced

All aspects of the API are exposed and customizable. The following options will not typically be used unless you need to change how a certain aspect of the API handles a use case.

Property	Type	Default	Description
generateSourceMap?	boolean or `(ms: MagicString, fileName: string) => SourceMap	undefined`	defaultGenerateSourceMap
strategy?	object	defaultStrategy	An object with methods defining how to minify HTML. The default strategy uses html-minifier.
validate?	boolean or object	defaultValidation	Set to false to disable strategy validation checks, or to a custom set of validation functions. This is only useful when implementing a custom strategy.
parseLiterals?	function	parse-literals	Override the function used to parse template literals from a source string.
parseLiteralsOptions?	object		Additional options to pass to parseLiterals()
MagicString?	function	MagicString	Override the MagicString-like constructor to use for manipulating the source string and generating source maps.

Customization Examples

Minify non-tagged templates

This is particularly useful for libraries that define templates without using tags, such as Polymer's <dom-module>.

import {
  minifyHTMLLiterals,
  defaultShouldMinify,
} from '@literals/html-css-minifier';

await minifyHTMLLiterals(
  `
    template.innerHTML = \`
      <dom-module id="custom-styles">
        <style>
          html {
            --custom-color: blue;
          }
        </style>
      </dom-module>
    \`;
  `,
  {
    fileName: 'render.js',
    shouldMinify(template) {
      return (
        defaultShouldMinify(template) ||
        template.parts.some((part) => {
          return part.text.includes('<dom-module>');
        })
      );
    },
  },
);

Do not minify CSS

import {
  minifyHTMLLiterals,
  defaultMinifyOptions,
} from '@literals/html-css-minifier';

await minifyHTMLLiterals(source, {
  fileName: 'render.js',
  minifyOptions: {
    ...defaultMinifyOptions,
    minifyCSS: false,
  },
  shouldMinifyCSS: () => false,
});

Modify generated SourceMap

await minifyHTMLLiterals(source, {
  fileName: 'render.js',
  generateSourceMap(ms, fileName) {
    return ms.generateMap({
      file: `${fileName}-converted.map`, // change file name
      source: fileName,
      includeContent: true, // include source contents
    });
  },
});