RIA and java script

As an entrepreneur, I believe that RIA could reduce the money payed for hosting compared with normal web applications (where the presentation is generated on server). I find ActionScript a good solution but the flow these days is with Html 5 and JavaScript even if it is not clear for me if that is what some big companies want or the customers (and the entrepreneurs) really need. Is JavaScript good enough for RIA? What Java Script frameworks would you use for real RIA?