Bill Sweetman looks up the current numbers for the JSF and the Harrier, and finds the following:

But the bottom line is this: with 2,500 pounds of weapons, plus the gun pod, the AV-8B has a hi-lo-hi operational radius of 508 nm. The F-35B’s design radius, with no gun, two 1,000-pound bombs and two AMRAAMs, is 450 nm: the most recent numbers (from 2007) show it exceeding that and just about equalling the AV-8B’s range.

Huh. Obviously, there are differences, a supersonic dash speed, some level of stealth, and a superior avionics suite, but it’s a less than impressive performance for an aircraft that will enter service about 30 years after the Harrier II.