Anyone playing in the "Web 2.0" domain, even if non-technical, has likely heard of such essential components of the Web applications style as AJAX and JSON. The 'J' in these acronyms stands for JavaScript, on which these standards are built. So the strengths and weaknesses of JavaScript are directly related to what can be built in the common Web 2.0 style, and therefore what business ideas can be implemented. Now there's another JavaScript related technology coming along quietly but quickly, and so far little noticed outside of developers' circles. It is called Caja, and it may have a major impact on what can and can't be accomplished by JavaScript-based Web 2.0 sites.