@leafac/html

Radically Straightforward HTML

Videos

Demonstration

Code Review

Installation

$ npm install @leafac/html

We recommend using @leafac/html along with the following tools:

Formatting: Prettier and the Visual Studio Code extension Prettier - Code formatter.

Syntax Highlighting: The Visual Studio Code extension es6-string-html.

Features, Usage, and Examples

Use tagged templates as an HTML template engine. For example:

import html from "@leafac/html";

console.log(html`<p>${"Leandro Facchinetti"}</p>`); // => <p>Leandro Facchinetti</p>

Safe by default. For example:

console.log(html`<p>${`<script>alert(1);</script>`}</p>`); // => <p>&#x3C;script&#x3E;alert(1);&#x3C;/script&#x3E;</p>

Unsafely interpolate trusted HTML with $${...}. For example:

console.log(html`<p>$${`<span>Leandro Facchinetti</span>`}</p>`); // => <p><span>Leandro Facchinetti</span></p>

Join interpolated arrays. For example:

console.log(html`<p>${["Leandro", " ", "Facchinetti"]}</p>`); // => <p>Leandro Facchinetti</p>

Array interpolation is safe by default; if you wish to unsafely interpolate an array of trusted HTML use $${[...]}.

@leafac/html doesn’t encode HTML itself. It relies on entities, which is a mature solution and covers all the edge cases.

@leafac/html doesn’t format the output. If you need pretty HTML, you may pass the output of @leafac/html to Prettier.

@leafac/html generates strings. No virtual DOM in sight. For readability, the HTML type is exported in TypeScript. For example:

import html, { HTML } from "@leafac/html";
const name: HTML = html`<p>Leandro Facchinetti</p>`;
console.log(name);

@leafac/html sanitizes (removes) invalid XML characters. It uses sanitize-xml-string. For example:

console.log(html`<p>A backspace is invalid in XML: ${`|\b|`}</p>`); // => <p>A backspace is invalid in XML: ||</p>

@leafac/html is fast. Rendering HTML tends to be one of the most expensive computations in a web server, so it must be fast. @leafac/html is more than one order of magnitude faster than ReactDOMServer.renderToStaticMarkup().

Related Projects

• https://npm.im/@leafac/sqlite: Radically Straightforward SQLite.
• https://npm.im/@leafac/css: Radically Straightforward CSS.
• https://npm.im/@leafac/javascript: Radically Straightforward Client-Side JavaScript.

Prior Art

• https://npm.im/html-template-tag:
  • Was a major inspiration for this. Its design is simple and great. In particular, I love (and stole) the idea of using $${...} to mark unsafe interpolation of trusted HTML.
  • Doesn’t encode arrays by default.
  • Uses a bespoke encoding.
• https://npm.im/common-tags:
  • Doesn’t encode interpolated values by default.
  • Uses the safeHtml tag, which isn’t recognized by Prettier or the Visual Studio Code extension es6-string-html extension.
• https://npm.im/escape-html-template-tag:
  • Less ergonomic API with escapeHtml.safe() and escapeHtml.join() instead of the $${} trick.
  • Uses a bespoke encoding.
• https://npm.im/lit-html, https://npm.im/nanohtml, https://npm.im/htm, and https://npm.im/viperhtml:
  • Have the notion of virtual DOM instead of simple string concatenation.

Changelog

4.0.1 · 2023-02-21

• Now it’s possible to import @leafac/html in the browser, which is useful for client-side components, for example, date pickers.
• Made @leafac/html 3.5x faster by changing from he entities.
• Switched from custom test runner to Node.js’s test runner.

4.0.0 · 2022-12-02

• Reimplemented @leafac/html to improve performance. Measured a 2x speedup with respect to version 3.0.3.

Breaking Changes

• Use default import instead of named import for html.

  Before:

  import { html, HTML } from "@leafac/html";

  After:

  import html, { HTML } from "@leafac/html";

• We no longer sanitize XML characters in the literal template or in unsafe substitutions (those using $${...}). This was one of the reasons for the performance improvement, particularly because it prevents the same string from being sanitized over and over in a big template with deep nesting.

  In most situations this change shouldn’t affect your code, but you must be aware of the following:

  • Templates must not contain invalid XML characters, for example, html`<p>A backspace: |\b|</p>`.
  • Unsafe substitutions (those using $${...}) must not contain invalid XML characters. If the unsafe substitution is the result of html`...` itself, then it’s already sanitized; but if you’re generating HTML in some other way, then you may need to introduce sanitize-xml-string’s sanitizeXMLCharacters.sanitize().

  Note: Safe substitutions (the default substitutions; those using ${...}) continued to be sanitized against invalid XML characters.