I’ve finished work on the first version of a client-side spellchecker written entirely in JavaScript, and I’m calling it Typo.js. Its express purpose is to allow Chrome extensions to perform spellchecking, although there’s no reason it wouldn’t work in other JavaScript environments. (Don’t use it for Firefox extensions though; use Firefox’s native spellchecking API.)

How does it work?

Typo.js uses Hunspell-style dictionaries – the same ones used in the spellcheckers of OpenOffice.org and Firefox. (Typo.js ships with the latest American English dictionary, but you could add any number of other dictionary files to it yourself.) You initialize a Typo.js instance in one of two ways:

Method #1

var dictionary = new Typo("en_US");

This tells Typo.js to load the dictionary represented by two files in the dictionaries/en_US/ directory: en_US.aff and en_US.dic. The .aff file is an affix file: a list of rules for creating multiple forms of a word by adding prefixes and suffixes. The .dic file is the dictionary file: a list of root words and the affix rules that apply to them. Typo parses these files and generates a complete dictionary by applying the applicable affix rules to the list of root words.

Method #2

var dictionary = new Typo("en_US", affData, dicData);

With this initialization method, you supply the data from the affix and dictionary files. This method is preferable if you wish to change the location of the affix and dictionary files or if you are using Typo.js in an environment other than a Chrome extension, such as in a webpage or in a server-side JavaScript environment.

Once you’ve initialized a Typo instance, you can use it to check whether a word is misspelled:

var is_correct_spelling = dictionary.check("mispelled");

Customization

Depending on your needs, you can configure Typo.js to perform word lookups in one of two ways:

1. hash: Stores the dictionary words as the keys of a hash and does a key existence check to determine whether a word is spelled correctly. Lookups are very fast, but this method uses more memory.
2. binary search: Concatenates dictionary words of identical length into sets of long strings and uses binary search in these strings to check whether a word exists in the dictionary. It uses less memory than the hash implementation, but lookups are slower.

See this blog post by John Resig for a more detailed exploration of possible dictionary representations in JavaScript.

Practice vs. Theory

Typo.js is already in use in my Comment Snob extension. You can install it today to experience Typo.js in action, filtering comments on YouTube based on the number of spelling mistakes in each one.

What’s next for Typo.js?

The next step is adding support for returning spelling suggestions; right now, all Typo.js can do is tell you whether a word is spelled correctly or not. It also needs to support Hunspell’s compound word rules. These are the rules that a spellchecker uses to determine whether words like “100th”, “101st”, “102th” are correct spellings (yes, yes, and no, for those of you keeping track) since it would be impossible to precompute a list of all possible words of these forms.

The Typo.js code is available on GitHub. I welcome any and all suggestions or code contributions.

Announcing Comment Snob

Comment Snob is an extension for Google Chrome that filters out undesirable comments from comment threads all over the Web.

Before:	After:

You can install it here. It still comes with support for YouTube built in, but you can add support for many other sites by installing Comment Snob rules.

What are Comment Snob Rules?

Comment Snob rules are JSON objects that dictate how Comment Snob finds and filters comments on different websites. Here’s the rule for YouTube that ships with Comment Snob:

{
	"id": "youtube@chrisfinke.com",
	"label": "YouTube",
	"url": "^http://www\\.youtube\\.com/.*$",
	"allCommentsSelector": "#comments-view",
	"commentContainerSelector": "li.comment",
	"commentTextSelector": "div.comment-text",
	"commentHideSelector": "> div",
	"statusElementTag": "div",
	"statusElementAttributes": {
		"class": "content",
		"style": "color: #666;"
	},
	"ajaxInitiatorSelector": ".comments-pagination button, .comments-pagination a, .comments-pagination button > span",
	"updateURL": "http://www.chrisfinke.com/comment-snob/rules/youtube.snob"
}

If you know HTML and understand how to use jQuery, you can write rules for Comment Snob. (Full instructions for writing rules are available here.)

For each rule that you install, you can choose a unique set of filtering rules:

Where Can I Install Rules?

I’ve written eight rules myself and made them available on this page (scroll down to “Featured Comment Snob Rules”); as other people write rules, I’ll link to them from that page as well. Eventually, I’ll have a proper site put together for showcasing the most popular rules.

Where Can I Install It?

Install it from the Google Chrome Extensions Gallery. It’s not available for Firefox yet, but I’ll most likely be releasing the next version for Chrome and Firefox simultaneously.

What’s Next?

This version of Comment Snob is just a shell of what my final vision is for comment filtering on the Web; right now, it’s all very manual, and the chances of false positives are too high for my taste. Adding a proper spellcheck filter will help that somewhat (Chrome doesn’t yet have a spellcheck API like Firefox does), but imagine a future where all comments on all websites could be filtered automatically based on their content, grammar, and keyword frequency, without having to account for personality differences between different websites. (e.g., The expected quality of a YouTube comment is much lower than the expected quality of a Hacker News comment, so Hacker News comments should be judged more stringently.) That starts to get close to what I want Comment Snob to be.

I got some great feedback after I updated URL Fixer to be compatible with Fennec, Mozilla’s mobile browser, and I’m happy to announce that I’ve been able to add Fennec compatibility to four more add-ons:

• TwitterBar: Post to Twitter from Firefox’s address bar
• AutoAuth: Automatically submits authentication dialogs
• YouTube Comment Snob (still in the sandbox): Filter out lame comments on YouTube
• Slashdotter (still in the sandbox): Adds features to the Slashdot website

So far, I’ve found it pretty easy to port add-ons to Fennec, with the following caveats:

• You can’t install add-ons in Fennec by opening them from your computer; I wrote a script to copy the add-on directly into the Fennec profile, much like an add-on IV drip – straight into the bloodstream!
• There’s no easy access to the error console , but you can open it manually if you grab the address from Firefox.
• No DOM Inspector. For now, just browse the source.

It seems that all of these issues could be solved with a “Fennec Add-on Development” extension; maybe that will be my next project, unless easier solutions already exist.

I’ve updated YouTube Comment Snob to work with YouTube’s latest redesign, as well as to add compatibility for Firefox 3. It’s available for download from the Mozilla Add-ons sandbox until it is approved by an AMO editor for mass consumption.

With the YouTube Comment Snob Firefox extension, you can hide comments that meet any of these criteria:

• More than # spelling mistakes: The number of mistakes is customizable, and the extension uses Firefox’s built-in spell checker.
• All capital letters
• No capital letters
• Doesn’t start with a capital letter
• Excessive punctuation (!!!! ????)
• Excessive capitalization

For example, here’s part of a typical YouTube comment thread:

And here’s how that same section looks when using YouTube Comment Snob:

(You’ll notice how foreign languages are categorized as spelling mistakes; if you speak a different language and have that dictionary installed for Firefox’s spellchecker, you can choose to have YouTube Comment Snob use that dictionary instead.)

You can install YouTube Comment Snob from its homepage. It is compatible with Firefox 1.5 through 3.0a7, Netscape Navigator 9, and Flock.