Type inference to make JavaScript as fast as statically typed languages?

Type Inference brings JS improvements to Firefox Beta” by Brian Hackett:
TI [Type Inference] is a feature in the SpiderMonkey Javascript engine which generates type information about Javascript programs through a combination of analyzing the program’s code and monitoring the types of values as the program executes.
With these projects, ... we hope to close the performance gap with Java completely.
Related talk: “JavaScript JITs” by David Mandelin and David Anderson at JSConf.eu 2011.