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Why ExtJS doc-comments suck

Why ExtJS doc-comments suck?

ExtJS comes with some heavy documentation, all generated directly from source code, which contains doc-comments like this:

/**
 * Get the index within the cache of the passed Record.
 * @param {Ext.data.Record} record The Ext.data.Record object to find.
 * @return {Number} The index of the passed Record. Returns -1 if not found.
 */
indexOf : function(record){

That's of course the good-old javadoc format, used by many-many languages nowadays, and the comment above looks perfectly readable. So, what's the problem?

HTML inside doc-comments

The problem is then when you need to add some structure to your comment, you have to use HTML. Just to start a new paragraph, you have to use <p> and when you want to add even more structure, say a list, the whole thing will get truly ugly:

/**
 * Find the index of the first matching Record in this Store by a function.
 * If the function returns <tt>true</tt> it is considered a match.
 * @param {Function} fn The function to be called. It will be passed the following
 * parameters:<ul>
 * <li><b>record</b> : Ext.data.Record<p class="sub-desc">The
 * {@link Ext.data.Record record} to test for filtering. Access field values using
 * {@link Ext.data.Record#get}.</p></li>
 * <li><b>id</b> : Object<p class="sub-desc">The ID of the Record passed.</p></li>
 * </ul>
 * @param {Object} scope (optional) The scope (<code>this</code> reference) in which
 * the function is executed. Defaults to this Store.
 * @param {Number} startIndex (optional) The index to start searching at
 * @return {Number} The matched index or -1
 */
findBy : function(fn, scope, start){

This comment is barely readable, and that's just one of them - ExtJS contains hundreds, if not thousands of comments like this. Comments formatted with HTML aren't easy to read, they aren't event easy to write. Just look at that example - in one place <tt> is used to mark up code, in another <code> is used. It even contains class names! So why? Why do they use HTML?

Sure, javadoc uses HTML, but nobody is going to run this code through javadoc. There's no need to be compatible with javadoc. Take for example PHPDocumentor - a tool for parsing doc comments in PHP - they support creating paragraphs and lists without HTML.

The only reason I can see, is that ExtJS has grown out of YUI, which also uses doc comments with HTML. But ExtJS isn't dependent from YUI, so there is no reason for the documentation to be.

But enough of bashing ExtJS, how could we make it better?

Markdown to the rescue

So, instead of using HTML, why not some other markup languge that's easier to read and write. Markdown is a good candidate for this role. (I'm using Markdown right now to write this blog-post). So, let's write the above doc-block using Markdown:

/**
 * Find the index of the first matching Record in this Store by a
 * function.  If the function returns `true` it is considered a
 * match.
 *
 * @param {Function} fn The function to be called.  It will be
 * passed the following parameters:
 *
 * - **record** : Ext.data.Record
 *
 *   The {@link Ext.data.Record record} to test for filtering.
 *   Access field values using {@link Ext.data.Record#get}.
 *
 * - **id** : Object
 *
 *   The ID of the Record passed.
 *
 * @param {Object} scope (optional) The scope (`this` reference)
 * in which the function is executed. Defaults to this Store.
 * @param {Number} startIndex (optional) The index to start
 * searching at
 * @return {Number} The matched index or -1
 */
findBy : function(fn, scope, start){

That's way more readable! Isn't it just obvious that this is the right solution!

It's also really easy to implement: Markdown implementations exist in several languages, it's just a matter of running the text-parts of doc-comment through a Markdown formatter. It's actually so easy, that it took me just one evening to add Markdown support for one of our internal documentation tools (it parses doc-comments of PHP files and generates HTML documentation for our AJAX API).

But there's more to ExtJS documentation...

Needless repetition

Look at the doc-block for Ext.data.Store.Error:

/**
 * @class Ext.data.Store.Error
 * @extends Ext.Error
 * Store Error extension.
 * @param {String} name
 */
Ext.data.Store.Error = Ext.extend(Ext.Error, {

This sure looks like a violation of the DRY principle. Isn't the class and it's parent obvious from the code? Couldn't the doc-comment parser figure it out by himself?

Here's my version:

/**
 * @class
 * Store Error extension.
 * @param {String} name
 */
Ext.data.Store.Error = Ext.extend(Ext.Error, {

Of course you can have situations where this information isn't easily extractable from the code. If that's the case, then it should be possible to explicitly define classname and parent classname in doc-comment, but it shouldn't be mandatory.

Another example is events:

/**
 * @event datachanged
 * Fires when the data cache has changed...
 * @param {Store} this
 */
'datachanged',

Or config options:

/**
 * @cfg {Boolean} autoSave
 * <p>Defaults to <tt>true</tt> causing the store to
 * automatically {@link #save} records...
 */
autoSave : true,

And then, surprise-surprise, somehow they got it right with properties:

/**
 * See the <code>{@link #baseParams corresponding configuration option}</code>
 * for a description of this property.
 * To modify this property see <code>{@link #setBaseParam}</code>.
 * @property
 */
this.baseParams = Ext.isObject(this.baseParams) ? this.baseParams : {};

This last example makes it pretty obvious that all that repetition can be easily avoided. It's just that... why isn't it avoided then?

Conclusions

It's bad that ExtJS doc-comments suck. It's not only the ExtJS team members who suffer, it's the whole community. It's unwritten standard that when you publish ExtJS extension, you should document your code in ExtJS-way. But when you try to do it, you will suffer. And so, many authors just don't bother.

Programmers don't like writing documentation, it's a nuisance. You have to make it really-really easy, or it just won't be done. That's why we have the doc-comments in the first place - to bring documenation as close to the code as possible. But you aren't really making documenting easier, when writing it involves some clumsy markup language. You really don't want to write your comments in XML (another great idea from Microsoft). HTML isn't much better either.

Is there any hope for a change? It doesn't look like ExtJS is going to do anything about it. (Well, nobody really knows what plans they have.) So our only hope is to do it by ourselves, for example by extending ext-doc to support Markdown inside comments.

I have been thinking about this for a long time. Maybe it's time for me to take some action...

Kirjutatud 14. märtsil 2010.

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