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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).

This fork was created to fix the CVE-2020-7774 vulnerability and keep dependencies up to date

License

DevExtreme Showdown is released under the BSD-3-Clause license.

Installation

Download tarball

You can download the latest release tarball directly from releases

npm (server-side)

npm install devextreme-showdown

CDN

You can also use one of several CDNs available:

• jsDelivr

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

• unpkg

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

Note: Replace <version tag> with an actual version you're interested in, for instance 1.0.0.

Quick Example

Node

1var showdown  = require('devextreme-showdown'),
2    converter = new showdown.Converter(),
3    text      = '# hello, markdown!',
4    html      = converter.makeHtml(text);

Browser

1var converter = new showdown.Converter(),
2    text      = '# hello, markdown!',
3    html      = converter.makeHtml(text);

Output

Both examples should output...

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

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

1showdown.setOption('optionKey', 'value');

Locally

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

• through the constructor

  1var converter = new showdown.Converter({optionKey: 'value'});

• through the setOption() method

  1var converter = new showdown.Converter();
  2converter.setOption('optionKey', 'value');

Getting an option

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

getOption()

1// Global
2var myOption = showdown.getOption('optionKey');
3
4//Local
5var myOption = converter.getOption('optionKey');

getOptions()

1// Global
2var showdownGlobalOptions = showdown.getOptions();
3
4//Local
5var thisConverterSpecificOptions = converter.getOptions();

Retrieve the default options

You can get showdown's default options with:

1var defaultOptions = showdown.getDefaultOptions();

Valid Options

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

  This:

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

  Becomes this:

  1<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)

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

  1# foo

  will be parsed as

  1<h3>foo</h3>

• 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
  

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

  1some text www.google.com

  will be parsed as

  1<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.

• 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:

  1some text with__underscores__in middle

  will be parsed as

  1<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.

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

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

  1| h1    |    h2   |      h3 |
  2|:------|:-------:|--------:|
  3| 100   | [a][1]  | ![b][2] |
  4| *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:

  1 - [x] This task is done
  2 - [ ] 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>, without needing 2 spaces at the end of the line (since v1.5.1)

  1a line  
  2wrapped in two

  turns into:

  1<p>a line<br>
  2wrapped 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>.

• 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)

  1var conv = new showdown.Converter({metadata: true});
  2var html = conv.makeHtml(someMd);
  3var 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

1showdown.setFlavor('github');

Instance

1converter.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

1<script src="showdown.js" />
2<script src="twitter-extension.js" />
3
4var converter = new showdown.Converter({ extensions: ['twitter'] });

Server-side Extension Usage

1var showdown    = require('devextreme-showdown'),
2    myExtension = require('myExtension'),
3    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.

Credits

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

Showdown is powered by: