@css-inline/css-inline

# css-inline [<img alt="build status" src="https://img.shields.io/github/actions/workflow/status/Stranger6667/css-inline/build.yml?style=flat-square&labelColor=555555&logo=github" height="20">](https://github.com/Stranger6667/css-inline/actions/workflows/build.yml) [<img alt="npm" src="https://img.shields.io/npm/v/@css-inline/css-inline.svg?style=flat-square" height="20">](https://www.npmjs.com/package/@css-inline/css-inline) [<img alt="codecov.io" src="https://img.shields.io/codecov/c/gh/Stranger6667/css-inline?logo=codecov&style=flat-square&token=tOzvV4kDY0" height="20">](https://app.codecov.io/github/Stranger6667/css-inline) [<img alt="gitter" src="https://img.shields.io/gitter/room/Stranger6667/css-inline?style=flat-square" height="20">](https://gitter.im/Stranger6667/css-inline) `css-inline` is a high-performance library for inlining CSS into HTML 'style' attributes. This library is designed for scenarios such as preparing HTML emails or embedding HTML into third-party web pages. For instance, the library transforms HTML like this: ```html <html> <head> <style>h1 { color:blue; }</style> </head> <body> <h1>Big Text</h1> </body> </html> ``` into: ```html <html> <head></head> <body> <h1 style="color:blue;">Big Text</h1> </body> </html> ``` - Uses reliable components from Mozilla's Servo project - Inlines CSS from `style` and `link` tags - Removes `style` and `link` tags - Resolves external stylesheets (including local files) - Optionally caches external stylesheets - Works on Linux, Windows, and macOS - Supports HTML5 & CSS3 - Tested on Node.js 18 & 20. ## Playground If you'd like to try `css-inline`, you can check the WebAssembly-powered [playground](https://css-inline.org/) to see the results instantly. ## Installation ### Node.js Install with `npm`: ```shell npm i @css-inline/css-inline ``` ## Usage ```typescript import { inline } from "@css-inline/css-inline"; var inlined = inline( ` <html> <head> <style>h1 { color:red }</style> </head> <body> <h1>Test</h1> </body> </html> `, ); // Do something with the inlined HTML, e.g. send an email ``` Note that `css-inline` automatically adds missing `html` and `body` tags, so the output is a valid HTML document. Alternatively, you can inline CSS into an HTML fragment, preserving the original structure: ```javascript import { inlineFragment } from "@css-inline/css-inline"; var inlined = inlineFragment( ` <main> <h1>Hello</h1> <section> <p>who am i</p> </section> </main> `, ` p { color: red; } h1 { color: blue; } ` ); // HTML becomes this: // <main> // <h1 style="color: blue;">Hello</h1> // <section> // <p style="color: red;">who am i</p> // </section> // </main> ``` ### Configuration - `inlineStyleTags`. Specifies whether to inline CSS from "style" tags. Default: `true` - `keepStyleTags`. Specifies whether to keep "style" tags after inlining. Default: `false` - `keepLinkTags`. Specifies whether to keep "link" tags after inlining. Default: `false` - `keepAtRules`. Specifies whether to keep "at-rules" (starting with `@`) after inlining. Default: `false` - `baseUrl`. The base URL used to resolve relative URLs. If you'd like to load stylesheets from your filesystem, use the `file://` scheme. Default: `null` - `loadRemoteStylesheets`. Specifies whether remote stylesheets should be loaded. Default: `true` - `cache`. Specifies caching options for external stylesheets (for example, `{size: 5}`). Default: `null` - `extraCss`. Extra CSS to be inlined. Default: `null` - `preallocateNodeCapacity`. **Advanced**. Preallocates capacity for HTML nodes during parsing. This can improve performance when you have an estimate of the number of nodes in your HTML document. Default: `32` You can also skip CSS inlining for an HTML tag by adding the `data-css-inline="ignore"` attribute to it: ```html <head> <style>h1 { color:blue; }</style> </head> <body>  <h1 data-css-inline="ignore">Big Text</h1> </body> </html> ``` The `data-css-inline="ignore"` attribute also allows you to skip `link` and `style` tags: ```html <head>  <style data-css-inline="ignore">h1 { color:blue; }</style> </head> <body> <h1>Big Text</h1> </body> ``` Alternatively, you may keep `style` from being removed by using the `data-css-inline="keep"` attribute. This is useful if you want to keep `@media` queries for responsive emails in separate `style` tags. Such tags will be kept in the resulting HTML even if the `keep_style_tags` option is set to `false`. ```html <head>  <style data-css-inline="keep">h1 { color:blue; }</style> </head> <body> <h1>Big Text</h1> </body> ``` Another possibility is to set `keep_at_rules` option to `true`. At-rules cannot be inlined into HTML therefore they get removed by default. This is useful if you want to keep at-rules, e.g. `@media` queries for responsive emails in separate `style` tags but inline any styles which can be inlined. Such tags will be kept in the resulting HTML even if the `keep_style_tags` option is explicitly set to `false`. ```html <head>  <style>h1 { color: blue; } @media (max-width: 600px) { h1 { font-size: 18px; } }</style> </head> <body> <h1>Big Text</h1> </body> ``` You can also cache external stylesheets to avoid excessive network requests: ```typescript import { inline } from "@css-inline/css-inline"; var inlined = inline( ` <html> <head> <link href="http://127.0.0.1:1234/external.css" rel="stylesheet"> <style>h1 { color:red }</style> </head> <body> <h1>Test</h1> </body> </html> `, { cache: { size: 5 } }, ); ``` Caching is disabled by default. ## WebAssembly `css-inline` also ships a WebAssembly module built with `wasm-bindgen` to run in browsers. ```html <script src="https://unpkg.com/@css-inline/css-inline-wasm"></script> <script> // Initialize the WASM module first cssInline.initWasm(fetch('https://unpkg.com/@css-inline/css-inline-wasm/index_bg.wasm')); const inlinedHtml = cssInline.inline(`<html> <head> <style>h1 { color:blue; }</style> </head> <body> <h1>Big Text</h1> </body> </html>`); document.getElementById('output').src = inlinedHtml </script> ``` **NOTE**: WASM module currently lacks support for fetching stylesheets from network or filesystem and caching. ## Performance `css-inline` is powered by efficient tooling from Mozilla's Servo project and significantly outperforms other JavaScript alternatives in terms of speed. Most of the time it achieves over a **3x** speed advantage compared to the next fastest alternative. Here is the performance comparison: | | Size | `css-inline 0.14.0` | `css-inline-wasm 0.13.0` | `juice 10.0.0` | `inline-css 4.0.2` | |-------------|---------|---------------------|--------------------------|-----------------------|----------------------| | Basic | 230 B | 16.82 µs | 20.92 µs (**1.24x**) | 57.00 µs (**3.38x**) | 68.43 µs (**4.06x**) | | Realistic-1 | 8.58 KB | 351.74 µs | 452.28 µs (**1.28x**) | 859.10 µs (**2.44x**) | 1.04 ms (**2.98x**) | | Realistic-2 | 4.3 KB | 203.25 µs | 269.54 µs (**1.32x**) | 1.02 ms (**5.04x**) | 861.32 µs (**4.23x**) | The "Basic" case was obtained from benchmarking the example from the Usage section. The benchmarking code is available in the `benches/bench.ts` file. The benchmarks were conducted using the stable `rustc 1.77.1` on Node.js `v21.1.0`. ## License This project is licensed under the terms of the [MIT license](https://opensource.org/licenses/MIT).