dotjs is a Google Chrome extension that executes JavaScript files in ~/.js based on their filename. If you navigate to google.com, dotjs will execute ~/.js/google.com.js. This makes it super easy to spruce up your favorite pages using JavaScript. Bonus: files in ~/.js have jQuery 1.6 loaded, regardless of whether the site you’re hacking uses jQuery. Double bonus: `~/.js/default.js` is loaded on every request, meaning you can stick plugins or helper functions in it.
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dotjs - Google Chrome Extension for Executing JavaScript - hack the web

dotjs is a Google Chrome extension that executes JavaScript files in ~/.js based on their filename.

If you navigate to google.com, dotjs will execute ~/.js/google.com.js.

This makes it super easy to spruce up your favorite pages using JavaScript.

Bonus: files in ~/.js have jQuery 1.6 loaded, regardless of whether the site you’re hacking uses jQuery.

Double bonus: `~/.js/default.js` is loaded on every request, meaning you can stick plugins or helper functions in it.

Source: defunkt.io