From the Twitter Engineering Blog:

Twitter typeahead.js is a fast and battle-tested jQuery plugin for auto completion. Today we’re open sourcing the code on GitHub under the MIT license. By sharing a piece of our infrastructure with the open source community, we hope to evolve typeahead.js further with community input.

When I first saw this, I thought, “What about Twitter Bootstrap’s auto completion jQuery plugin? How do they compare?”

In the readme, it talks about Bootstrap Integration:

• If you’re customizing Bootstrap, exclude the typeahead component. If you’re depending on the standard bootstrap.js, ensure typeahead.js is loaded after it.
• The DOM structure of the dropdown menu used by typeahead.js differs from the DOM structure of the Bootstrap dropdown menu. You’ll need to load some additional CSS in order to get the typeahead.js dropdown menu to fit the default Bootstrap theme.