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316 lines
11 KiB
Markdown
316 lines
11 KiB
Markdown
# Showdown
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A JavaScript port of Markdown
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## Note
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> Showdown is now maintained by the [showdownjs](https://github.com/showdownjs) organization on Github.
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>
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> The organization needs members to maintain Showdown.
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>
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> Please see [this issue](https://github.com/showdownjs/showdown/issues/114) to express interest or comment on this note.
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## Original Attributions
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Showdown Copyright (c) 2007 John Fraser.
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<http://www.attacklab.net/>
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Original Markdown Copyright (c) 2004-2005 John Gruber
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<http://daringfireball.net/projects/markdown/>
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Redistributable under a BSD-style open source license.
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See license.txt for more information.
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## Quick Example
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```js
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var Showdown = require('showdown');
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var converter = new Showdown.converter();
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converter.makeHtml('#hello markdown!');
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// <h1 id="hellomarkdown">hello, markdown</h1>
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```
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## What's it for?
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Developers can use Showdown to:
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* Add in-browser preview to existing Markdown apps
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Showdown's output is (almost always) identical to
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markdown.pl's, so the server can reproduce exactly
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the output that the user saw. (See below for
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exceptions.)
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* Add Markdown input to programs that don't support it
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Any app that accepts HTML input can now be made to speak
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Markdown by modifying the input pages's HTML. If your
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application lets users edit documents again later,
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then they won't have access to the original Markdown
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text. But this should be good enough for many
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uses -- and you can do it with just a two-line
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`onsubmit` function!
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* Add Markdown input to closed-source web apps
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You can write bookmarklets or userscripts to extend
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any standard textarea on the web so that it accepts
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Markdown instead of HTML. With a little more hacking,
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the same can probably be done with many rich edit
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controls.
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* Build new web apps from scratch
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A Showdown front-end can send back text in Markdown,
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HTML or both, so you can trade bandwidth for server
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load to reduce your cost of operation. If your app
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requires JavaScript, you won't need to do any
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Markdown processing on the server at all. (For most
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uses, you'll still need to sanitize the HTML before
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showing it to other users -- but you'd need to do
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that anyway if you're allowing raw HTML in your
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Markdown.)
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## Browser Compatibility
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Showdown has been tested successfully with:
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* Firefox 1.5 and 2.0
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* Internet Explorer 6 and 7
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* Safari 2.0.4
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* Opera 8.54 and 9.10
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* Netscape 8.1.2
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* Konqueror 3.5.4
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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.
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## Extensions
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Showdown allows additional functionality to be loaded via extensions.
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### Client-side Extension Usage
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```js
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<script src="src/showdown.js" />
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<script src="src/extensions/twitter.js" />
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var converter = new Showdown.converter({ extensions: 'twitter' });
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```
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### Server-side Extension Usage
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```js
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// Using a bundled extension
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var Showdown = require('showdown');
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var converter = new Showdown.converter({ extensions: ['twitter'] });
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// Using a custom extension
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var mine = require('./custom-extensions/mine');
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var converter = new Showdown.converter({ extensions: ['twitter', mine] });
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```
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## Known Differences in Output
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In most cases, Showdown's output is identical to that of Perl Markdown v1.0.2b7. What follows is a list of all known deviations. Please file an issue if you find more.
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* This release uses the HTML parser from Markdown 1.0.2b2,
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which means it fails `Inline HTML (Advanced).text` from
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the Markdown test suite:
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<div>
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<div>
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unindented == broken
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</div>
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</div>
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* Showdown doesn't support the markdown="1" attribute:
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<div markdown="1">
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Markdown does *not* work in here.
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</div>
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This is half laziness on my part and half stubbornness.
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Markdown is smart enough to process the contents of span-
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level tags without screwing things up; shouldn't it be
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able to do the same inside block elements? Let's find a
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way to make markdown="1" the default.
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* You can only nest square brackets in link titles to a
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depth of two levels:
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[[fine]](http://www.attacklab.net/)
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[[[broken]]](http://www.attacklab.net/)
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If you need more, you can escape them with backslashes.
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* When sublists have paragraphs, Showdown produces equivalent
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HTML with a slightly different arrangement of newlines:
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+ item
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- subitem
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The HTML has a superfluous newline before this
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paragraph.
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- subitem
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The HTML here is unchanged.
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- subitem
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The HTML is missing a newline after this
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list subitem.
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* Markdown.pl creates empty title attributes for
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inline-style images:
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Here's an empty title on an inline-style
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.
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I tried to replicate this to clean up my diffs during
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testing, but I went too far: now Showdown also makes
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empty titles for reference-style images:
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Showdown makes an empty title for
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reference-style ![images][] too.
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[images]: http://w3.org/Icons/valid-xhtml10
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* With crazy input, Markdown will mistakenly put
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`<strong>` or `<em>` tags in URLs:
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<a href="<*Markdown adds em tags in here*>">
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improbable URL
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</a>
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Showdown won't. But still, don't do that.
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## Tests
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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 development dependencies:
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npm install --dev
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Once installed the tests can be run from the project root using:
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npm test
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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`.
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## Creating Markdown Extensions
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A showdown extension is simply a function which returns an array of extensions. Each single extension can be one of two types:
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* Language Extension -- Language extensions are ones that that add new markdown syntax to showdown. For example, say you wanted `^^youtube http://www.youtube.com/watch?v=oHg5SJYRHA0` to automatically render as an embedded YouTube video, that would be a language extension.
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* Output Modifiers -- After showdown has run, and generated HTML, an output modifier would change that HTML. For example, say you wanted to change `<div class="header">` to be `<header>`, that would be an output modifier.
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Each extension can provide two combinations of interfaces for showdown.
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### Regex/Replace
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Regex/replace style extensions are very similar to javascripts `string.replace` function. Two properties are given, `regex` and `replace`. `regex` is a string and `replace` can be either a string or a function. If `replace` is a string, it can use the `$1` syntax for group substitution, exactly as if it were making use of `string.replace` (internally it does this actually); The value of `regex` is assumed to be a global replacement.
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**Example:**
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```js
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var demo = function(converter) {
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return [
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// Replace escaped @ symbols
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{ type: 'lang', regex: '\\@', replace: '@' }
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];
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}
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```
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### Filter
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Alternately, if you'd just like to do everything yourself, you can specify a filter which is a callback with a single input parameter, text (the current source text within the showdown engine).
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**Example:**
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```js
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var demo = function(converter) {
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return [
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// Replace escaped @ symbols
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{ type: 'lang', filter: function(text) {
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return text.replace(/\\@/g, '@');
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}}
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];
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}
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```
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### Implementation Concerns
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One bit which should be taken into account is maintaining both client-side and server-side compatibility. This can be achieved with a few lines of boilerplate code. First, to prevent polluting the global scope for client-side code, the extension definition should be wrapped in a self-executing function.
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```js
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(function(){
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// Your extension here
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}());
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```
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Second, client-side extensions should add a property onto `Showdown.extensions` which matches the name of the file. As an example, a file named `demo.js` should then add `Showdown.extensions.demo`. Server-side extensions can simply export themselves.
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```js
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(function(){
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var demo = function(converter) {
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// ... extension code here ...
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};
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// Client-side export
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if (typeof window !== 'undefined' && window.Showdown && window.Showdown.extensions) { window.Showdown.extensions.demo = demo; }
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// Server-side export
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if (typeof module !== 'undefined') module.exports = demo;
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}());
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```
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### Testing Extensions
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The showdown test runner is setup to automatically test cases for extensions. To add test cases for an extension, create a new folder under `./test/extensions` which matches the name of the `.js` file in `./src/extensions`. Place any test cases into the filder using the md/html format and they will automatically be run when tests are run.
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## Credits
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* Origins
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* [John Fraser](http://attacklab.net/):<br/>
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Author of Showdown
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* [John Gruber](http://daringfireball.net/projects/markdown/):<br/>
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Author of Markdown
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* Maintenance/Contributions (roughly chronologically)
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* [Corey Innis](http://github.com/coreyti):<br/>
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GitHub project maintainer
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* [Remy Sharp](https://github.com/remy/):<br/>
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CommonJS-compatibility and more
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* [Konstantin Käfer](https://github.com/kkaefer/):<br/>
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CommonJS packaging
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* [Roger Braun](https://github.com/rogerbraun):<br/>
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Github-style code blocks
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* [Dominic Tarr](https://github.com/dominictarr):<br/>
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Documentation
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* [Cat Chen](https://github.com/CatChen):<br/>
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Export fix
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* [Titus Stone](https://github.com/tstone):<br/>
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Mocha tests, extension mechanism, and bug fixes
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* [Rob Sutherland](https://github.com/roberocity):<br/>
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The idea that lead to extensions
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* [Pavel Lang](https://github.com/langpavel):<br/>
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Code cleanup
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* [Ben Combee](https://github.com/unwiredben):<br/>
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Regex optimization
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* [Adam Backstrom](https://github.com/abackstrom):<br/>
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WebKit bugfix
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* [Pascal Deschênes](https://github.com/pdeschen):<br/>
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Grunt support, extension fixes + additions, packaging improvements, documentation
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