showdown

What is showdown?

Showdown is a JavaScript Markdown to HTML converter, based on the original works by John Gruber. It allows you to easily convert Markdown text into HTML, making it useful for web applications, documentation, and other text processing tasks.

What are showdown's main functionalities?

Convert Markdown to HTML

This feature allows you to convert Markdown text into HTML. The code sample demonstrates how to create a new Showdown converter instance and use it to convert a Markdown string into HTML.

const showdown = require('showdown');
const converter = new showdown.Converter();
const markdown = '# Hello, Showdown!';
const html = converter.makeHtml(markdown);
console.log(html);

Customize Output

Showdown allows you to customize the output by enabling or disabling various options. The code sample shows how to enable the 'tables' and 'strikethrough' options to enhance the Markdown to HTML conversion.

const showdown = require('showdown');
const converter = new showdown.Converter({ tables: true, strikethrough: true });
const markdown = '~~Strikethrough~~ and a table:

| h1 | h2 |
| --- | --- |
| cell1 | cell2 |';
const html = converter.makeHtml(markdown);
console.log(html);

Extension Support

Showdown supports extensions, allowing you to add custom functionality to the conversion process. The code sample demonstrates how to create a simple extension that converts '@text' into bold HTML text.

const showdown = require('showdown');
showdown.extension('myextension', function() {
  return [{
    type: 'lang',
    regex: /@(	ext)/g,
    replace: '<strong>$1</strong>'
  }];
});
const converter = new showdown.Converter({ extensions: ['myextension'] });
const markdown = 'This is @text.';
const html = converter.makeHtml(markdown);
console.log(html);

Other packages similar to showdown

marked

Marked is a fast, lightweight Markdown parser and compiler. It is designed for speed and offers a high level of customization. Compared to Showdown, Marked is often preferred for its performance and flexibility in handling large Markdown files.

markdown-it

Markdown-it is a powerful Markdown parser that offers a wide range of features, including plugins and high-speed performance. It is known for its extensibility and ability to handle complex Markdown syntax. Markdown-it provides more advanced features and customization options compared to Showdown.

remark

Remark is a Markdown processor powered by plugins. It is part of the unified collective and offers a highly modular and extensible approach to Markdown processing. Remark is suitable for users who need a highly customizable and plugin-based solution, whereas Showdown is more straightforward and easier to use out of the box.

README

---

Showdown is a Javascript Markdown to HTML converter, based on the original works by John Gruber. Showdown can be used client side (in the browser) or server side (with NodeJs).

Live DEMO

Check a live Demo here http://demo.showdownjs.com/

Funding

As you know, ShowdownJS is a free library and it will remain free forever. However, maintaining and improving the library costs time and money.

If you like our work and find our library useful, please donate through paypal!! Your contribution will be greatly appreciated and help us continue to develop this awesome library.

License

ShowdownJS v 2.0 is release under the MIT version. Previous versions are release under BSD.

Who uses Showdown (or a fork)

• GoogleCloudPlatform
• Meteor
• Stackexchange - forked as PageDown
• docular
• md-page
• QCObjects
• and some others...

Installation

Download tarball

You can download the latest release tarball directly from releases

Bower

bower install showdown

npm (server-side)

npm install showdown

NuGet package

PM> Install-Package showdownjs

The NuGet Packages can be found here.

CDN

You can also use one of several CDNs available:

• jsDelivr

    https://cdn.jsdelivr.net/npm/showdown@<version tag>/dist/showdown.min.js
  

• cdnjs

    https://cdnjs.cloudflare.com/ajax/libs/showdown/<version tag>/showdown.min.js
  

• unpkg

    https://unpkg.com/showdown/dist/showdown.min.js
  

Note: replace <version tag> with an actual full length version you're interested in e.g. 1.9.0

Browser Compatibility

Showdown has been tested successfully with:

• Firefox 1.5 and 2.0
• Chrome 12.0
• Internet Explorer 6 and 7
• Safari 2.0.4
• Opera 8.54 and 9.10
• Netscape 8.1.2
• Konqueror 3.5.4

In theory, Showdown will work in any browser that supports ECMA 262 3rd Edition (JavaScript 1.5). The converter itself might even work in things that aren't web browsers, like Acrobat. No promises.

Node compatibility

Showdown supports node versions in the "Current", "Active" and "Maintenance" phases. Currently this includes Node 12.x, 14.x, 16.x and 17.x. See the [node release roadmap for more details](12.x, 14.x, 16.x, 17.x).

Other versions of node may likely work, but they are not tested regularly.

Pervious versions

If you're looking for showdown v<1.0.0, you can find it in the legacy branch.

If you are looking for showdown 1.* you can find it in the [version_1.x][version_1.x] branch.

Changelog

You can check the full changelog

Extended documentation

Check our wiki pages for examples and a more in-depth documentation.

Quick Example

Node

Markdown to HTML

var showdown  = require('showdown'),
    converter = new showdown.Converter(),
    text      = '# hello, markdown!',
    html      = converter.makeHtml(text);

HTML to Markdown

var showdown  = require('showdown'),
    converter = new showdown.Converter(),
    html      = '<a href="https://patreon.com/showdownjs">Please Support us!</a>',
    md        = converter.makeMarkdown(text);

Browser

var converter = new showdown.Converter(),
    html      = converter.makeHtml('# hello, markdown!'),
    md        = converter.makeMd('<a href="https://patreon.com/showdownjs">Please Support us!</a>');

Output

Both examples should output...

    <h1 id="hellomarkdown">hello, markdown!</h1>

[Please Support us!](https://patreon.com/showdownjs)

Options

You can change some of showdown's default behavior through options.

Setting options

Options can be set:

Globally

Setting a "global" option affects all instances of showdown

showdown.setOption('optionKey', 'value');

Locally

Setting a "local" option only affects the specified Converter object. Local options can be set:

• through the constructor

  var converter = new showdown.Converter({optionKey: 'value'});
  

• through the setOption() method

  var converter = new showdown.Converter();
  converter.setOption('optionKey', 'value');
  

Getting an option

Showdown provides 2 methods (both local and global) to retrieve previous set options.

getOption()

// Global
var myOption = showdown.getOption('optionKey');

//Local
var myOption = converter.getOption('optionKey');

getOptions()

// Global
var showdownGlobalOptions = showdown.getOptions();

//Local
var thisConverterSpecificOptions = converter.getOptions();

Retrieve the default options

You can get showdown's default options with:

var defaultOptions = showdown.getDefaultOptions();

Valid Options

• omitExtraWLInCodeBlocks: (boolean) [default false] Omit the trailing newline in a code block. Ex:

  This:

  <code><pre>var foo = 'bar';
  </pre></code>
  

  Becomes this:

  <code><pre>var foo = 'bar';</pre></code>
  

• noHeaderId: (boolean) [default false] Disable the automatic generation of header ids. Setting to true overrides prefixHeaderId

• customizedHeaderId: (boolean) [default false] Use text in curly braces as header id. (since v1.7.0) Example:

  ## Sample header {real-id}     will use real-id as id
  

• ghCompatibleHeaderId: (boolean) [default false] Generate header ids compatible with github style (spaces are replaced with dashes and a bunch of non alphanumeric chars are removed) (since v1.5.5)

• prefixHeaderId: (string/boolean) [default false] Add a prefix to the generated header ids. Passing a string will prefix that string to the header id. Setting to true will add a generic 'section' prefix.

• rawPrefixHeaderId: (boolean) [default false] Setting this option to true will prevent showdown from modifying the prefix. This might result in malformed IDs (if, for instance, the " char is used in the prefix). Has no effect if prefixHeaderId is set to false. (since v 1.7.3)

• rawHeaderId: (boolean) [default false] Remove only spaces, ' and " from generated header ids (including prefixes), replacing them with dashes (-). WARNING: This might result in malformed ids (since v1.7.3)

• parseImgDimensions: (boolean) [default false] Enable support for setting image dimensions from within markdown syntax. Examples:

  ![foo](foo.jpg =100x80)     simple, assumes units are in px
  ![bar](bar.jpg =100x*)      sets the height to "auto"
  ![baz](baz.jpg =80%x5em)  Image with width of 80% and height of 5em
  

• headerLevelStart: (integer) [default 1] Set the header starting level. For instance, setting this to 3 means that

  # foo
  

  will be parsed as

  <h3>foo</h3>
  

• simplifiedAutoLink: (boolean) [default false] Turning this option on will enable automatic linking to urls. This means that:

  some text www.google.com
  

  will be parsed as

  <p>some text <a href="www.google.com">www.google.com</a>
  

• excludeTrailingPunctuationFromURLs: (boolean) [default false] This option excludes trailing punctuation from autolinking urls. Punctuation excluded: . ! ? ( ). Only applies if simplifiedAutoLink option is set to true.

  check this link www.google.com!
  

  will be parsed as

  <p>check this link <a href="www.google.com">www.google.com</a>!</p>
  

• literalMidWordUnderscores: (boolean) [default false] Turning this on will stop showdown from interpreting underscores in the middle of words as <em> and <strong> and instead treat them as literal underscores.

  Example:

  some text with__underscores__in middle
  

  will be parsed as

  <p>some text with__underscores__in middle</p>
  

• literalMidWordAsterisks: (boolean) [default false] Turning this on will stop showdown from interpreting asterisks in the middle of words as <em> and <strong> and instead treat them as literal asterisks.

  Example:

  some text with**underscores**in middle
  

  will be parsed as

  <p>some text with**underscores**in middle</p>
  

• strikethrough: (boolean) [default false] Enable support for strikethrough syntax. ~~strikethrough~~ as <del>strikethrough</del>

• tables: (boolean) [default false] Enable support for tables syntax. Example:

  | h1    |    h2   |      h3 |
  |:------|:-------:|--------:|
  | 100   | [a][1]  | ![b][2] |
  | *foo* | **bar** | ~~baz~~ |
  

  See the wiki for more info

• tablesHeaderId: (boolean) [default false] If enabled adds an id property to table headers tags.

• ghCodeBlocks: (boolean) [default true] Enable support for GFM code block style.

• tasklists: (boolean) [default false] Enable support for GFM tasklists. Example:

   - [x] This task is done
   - [ ] This is still pending
  

• smoothLivePreview: (boolean) [default false] Prevents weird effects in live previews due to incomplete input

• smartIndentationFix: (boolean) [default false] Tries to smartly fix indentation problems related to es6 template strings in the midst of indented code.

• disableForced4SpacesIndentedSublists: (boolean) [default false] Disables the requirement of indenting sublists by 4 spaces for them to be nested, effectively reverting to the old behavior where 2 or 3 spaces were enough. (since v1.5.0)

• simpleLineBreaks: (boolean) [default false] Parses line breaks as <br>, like GitHub does, without needing 2 spaces at the end of the line (since v1.5.1)

  a line  
  wrapped in two
  

  turns into:

  <p>a line<br>
  wrapped in two</p>
  

• requireSpaceBeforeHeadingText: (boolean) [default false] Makes adding a space between # and the header text mandatory (since v1.5.3)

• ghMentions: (boolean) [default false] Enables github @mentions, which link to the username mentioned (since v1.6.0)

• ghMentionsLink: (string) [default https://github.com/{u}] Changes the link generated by @mentions. Showdown will replace {u} with the username. Only applies if ghMentions option is enabled. Example: @tivie with ghMentionsOption set to //mysite.com/{u}/profile will result in <a href="//mysite.com/tivie/profile">@tivie</a>

• encodeEmails: (boolean) [default true] Enable e-mail addresses encoding through the use of Character Entities, transforming ASCII e-mail addresses into its equivalent decimal entities. (since v1.6.1)

  NOTE: Prior to version 1.6.1, emails would always be obfuscated through dec and hex encoding.

• openLinksInNewWindow: (boolean) [default false] Open all links in new windows (by adding the attribute target="_blank" to <a> tags) (since v1.7.0)

• backslashEscapesHTMLTags: (boolean) [default false] Support for HTML Tag escaping. ex: \<div>foo\</div> (since v1.7.2)

• emoji: (boolean) [default false] Enable emoji support. Ex: this is a :smile: emoji For more info on available emojis, see https://github.com/showdownjs/showdown/wiki/Emojis (since v.1.8.0)

• underline: (boolean) [default false] EXPERIMENTAL FEATURE Enable support for underline. Syntax is double or triple underscores ex: __underlined word__. With this option enabled, underscores are no longer parses into <em> and <strong>.

• ellipsis: (boolean) [default true] Replaces three dots with the ellipsis unicode character.

• completeHTMLDocument: (boolean) [default false] Outputs a complete html document, including <html>, <head> and <body> tags' instead of an HTML fragment. (since v.1.8.5)

• metadata: (boolean) [default false] Enable support for document metadata (defined at the top of the document between ««« and »»» or between --- and ---). (since v.1.8.5)

  var conv = new showdown.Converter({metadata: true});
  var html = conv.makeHtml(someMd);
  var metadata = conv.getMetadata(); // returns an object with the document metadata
  

• splitAdjacentBlockquotes: (boolean) [default false] Split adjacent blockquote blocks.(since v.1.8.6)

NOTE: Please note that until version 1.6.0, all of these options are DISABLED by default in the cli tool.

Flavors

You can also use flavors or presets to set the correct options automatically, so that showdown behaves like popular markdown flavors.

Currently, the following flavors are available:

• original - original markdown flavor as in John Gruber's spec
• vanilla - showdown base flavor (as from v1.3.1)
• github - GFM (GitHub Flavored Markdown)

Global

showdown.setFlavor('github');

Instance

converter.setFlavor('github');

CLI Tool

Showdown also comes bundled with a Command Line Interface tool. You can check the CLI wiki page for more info

Integration with AngularJS

ShowdownJS project also provides seamlessly integration with AngularJS via a "plugin". Please visit https://github.com/showdownjs/ngShowdown for more information.

Integration with TypeScript

If you're using TypeScript you maybe want to use the types from DefinitelyTyped

Integration with SystemJS/JSPM

Integration with SystemJS can be obtained via the third party "system-md" plugin.

Integration with VueJS

To use ShowdownJS as a Vue component quickly, you can check vue-showdown.

XSS vulnerability

Showdown doesn't sanitize the input. This is by design since markdown relies on it to allow certain features to be correctly parsed into HTML. This, however, means XSS injection is quite possible.

Please refer to the wiki article Markdown's XSS Vulnerability (and how to mitigate it) for more information.

Extensions

Showdown allows additional functionality to be loaded via extensions. (you can find a list of known showdown extensions here) You can also find a boilerplate, to create your own extensions in this repository

Client-side Extension Usage

<script src="showdown.js"></script>
<script src="twitter-extension.js"></script>
<script>
var converter = new showdown.Converter({ extensions: ['twitter'] });
</script>

Server-side Extension Usage

var showdown    = require('showdown'),
    myExtension = require('myExtension'),
    converter = new showdown.Converter({ extensions: ['myExtension'] });

Tests

A suite of tests is available which require node.js. Once node is installed, run the following command from the project root to install the dependencies:

npm install

Once installed the tests can be run from the project root using:

npm test

New test cases can easily be added. Create a markdown file (ending in .md) which contains the markdown to test. Create a .html file of the exact same name. It will automatically be tested when the tests are executed with mocha.

Contributing

If you wish to contribute please read the following quick guide.

Want a Feature?

You can request a new feature by submitting an issue. If you would like to implement a new feature feel free to issue a Pull Request.

Pull requests (PRs)

PRs are awesome. However, before you submit your pull request consider the following guidelines:

• Search GitHub for an open or closed Pull Request that relates to your submission. You don't want to duplicate effort.

• When issuing PRs that change code, make your changes in a new git branch based on master:

  git checkout -b my-fix-branch master
  

• Documentation (i.e: README.md) changes can be made directly against master.

• Run the full test suite before submitting and make sure all tests pass (obviously =P).

• Try to follow our coding style rules. Breaking them prevents the PR to pass the tests.

• Refrain from fixing multiple issues in the same pull request. It's preferable to open multiple small PRs instead of one hard to review big one.

• If the PR introduces a new feature or fixes an issue, please add the appropriate test case.

• We use commit notes to generate the changelog. It's extremely helpful if your commit messages adhere to the AngularJS Git Commit Guidelines.

• If we suggest changes then:

  • Make the required updates.
  • Re-run the Angular test suite to ensure tests are still passing.
  • Rebase your branch and force push to your GitHub repository (this will update your Pull Request):

  git rebase master -i
  git push origin my-fix-branch -f
  

• After your pull request is merged, you can safely delete your branch.

If you have time to contribute to this project, we feel obliged that you get credit for it. These rules enable us to review your PR faster and will give you appropriate credit in your GitHub profile. We thank you in advance for your contribution!

Joining the team

We're looking for members to help maintaining Showdown. Please see this issue to express interest or comment on this note.

Credits

Full credit list at https://github.com/showdownjs/showdown/blob/master/CREDITS.md

Showdown is powered by:

Changelog

2.1.0 (2022-04-21)

• refactor(cli)!: Remove support for "extra options" and add -c flag, closes #916

Bug Fixes

• cli: cli displays the correct version number (8b48882)

BREAKING CHANGES

• the CLI no longer accepts "extra options". Instead you should pass the -c flag. To update:

before:

showdown makehtml -i foo.md -o bar.html --strikethrough --emoji

after:

showdown makehtml -i foo.md -o bar.html -c strikethrough -c emoji

<a name="2.0.0"></a>

Breaking Changes

• Supported Node Versions were set to match the node release schedule which at the time of writing includes Node 12.x, 14.x, 16.x and 17.x
• The yargs dependecy was updated to ^17.2.1 to mitigate a security issue.
• The Showdown Licesnse has been changed from BSD-3-Clause to MIT

Bug Fixes

• allow escaping of colons (25c4420)
• reduce npm package size (35730b7), closes #619

Features

• Added ellipsis option to configure if the ellipsis unicode character is used or not. ( Thanks @VladimirV99 )
• Added a default security policy. Please report security issues to the issues tab on GitHub.

<a name="1.9.1"></a>