sanitize-markdown

Lean and configurable allowlist-oriented HTML sanitizer

⚠️ A temporary fork of https://github.com/bevacqua/insane while https://github.com/bevacqua/insane/issues/16 is pending ⚠️

Works well in browsers, as its footprint size is very small (around ~2kb gzipped). API inspired by sanitize-html (which is around 100kb gzipped).

Install

npm install sanitize --save

Usage

sanitizeMarkdown('<div>foo<span>bar</span></div>', { allowedTags: ['div'] })
// <- '<div>foo</div>'

Contrary to similar sanitizers, sanitize-markdown drops the whole tree of descendants for elements that aren't allowed tags.

API

sanitizeMarkdown(html, options?, strict?)

• html can be an arbitrary HTML string
• options are detailed below
• strict means that options won't be based off of sanitizeMarkdown.defaults if set to true

The parser takes into account that some elements can be self-closing. For safety reasons the sanitizer will only accept a valid URL for background, base, cite, href, longdesc, src, and usemap elements. "Valid URL" means that it begins with either #, /, or any of options.allowedSchemes (followed by :).

options

Sensible defaults are provided. You can override specific options as needed.

allowedSchemes

Defaults to ['http', 'https', 'mailto'].

allowedTags

An array of tags that you'll allow in the resulting HTML.

Example

Only allow spans, discarding the rest of elements.

sanitizeMarkdown('<div>foo</div><span>bar</span>', {
  allowedTags: ['span']
});
// <- '<span>bar</span>'

allowedAttributes

An object describing the attributes you'll allow for each individual tag name.

allowedAttributes Example

Only allow spans, and only allow those spans to have an id (discarding the rest of their attributes).

sanitizeMarkdown('<span id="bar" class="super">bar</span>', {
  allowedTags: ['span'],
  allowedAttributes: { span: ['id'] }
});
// <- '<span id="bar">bar</span>'

allowedClasses

If 'class' is listed as an allowed attribute, every single class will be allowed. If you don't list 'class' as an allowed attribute, you can provide a class allowlist per tag name.

allowedClasses Example

Only allow spans to have super or bad class names, discarding the rest of them.

sanitizeMarkdown('<span class="super mean and bad">bar</span>', {
  allowedTags: ['span'],
  allowedClasses: { span: ['super', 'bad'] }
});
// <- '<span class="super bad">bar</span>'

filter

Takes a function(token) that allows you to do additional validation beyond exact tag name and attribute matching. The token object passed to your filter contains the following properties.

• tag is the lowercase tag name of the element
• attrs is an object containing every attribute in the element, including those that may not be in the allowlist

If you return a falsy value the element and all of its descendants will not be included in the output. Note that you are allowed to change the attrs, and even add new ones, transforming the output.

filter Example

Require that <span> elements have an aria-label value.

function filter (token) {
  return token.tag !== 'span' || token.attrs['aria-label'];
}
sanitizeMarkdown('<span aria-label="a foo">foo</span><span>bar</span>', {
  allowedTags: ['span'],
  allowedAttributes: { span: ['aria-label'] },
  filter: filter
});
// <- '<span aria-label="a foo">foo</span>'

transformText

Takes a function(text) that allows you to modify text content in HTML elements. Runs for every piece of text content. The returned value is used instead of the original text contents.

Defaults

The default configuration is used if you don't provide any. This object is available at sanitizeMarkdown.defaults. You are free to manipulate the defaults themselves.

{
  "allowedAttributes": {
    "a": ["href", "name", "target"],
    "iframe": ["allowfullscreen", "frameborder", "src"],
    "img": ["src"]
  },
  "allowedClasses": {},
  "allowedSchemes": ["http", "https", "mailto"],
  "allowedTags": [
    "a", "article", "b", "blockquote", "br", "caption", "code", "del", "details", "div", "em",
    "h1", "h2", "h3", "h4", "h5", "h6", "hr", "i", "img", "ins", "kbd", "li", "main", "ol",
    "p", "pre", "section", "span", "strike", "strong", "sub", "summary", "sup", "table",
    "tbody", "td", "th", "thead", "tr", "u", "ul"
  ],
  "filter": null,
  "transformText": null
}

License

MIT