I know both languages are from the same ECMA-262 standard. It seems that the two are becoming very similar with JavaScript adding event listeners for core Object instances t
One is type Safetly. Actionscript requires that you set a type for all objects, and JavaScript doesn't (for that matter, in JavaScript, one variable may be one type and then immediately set to another type).
Actionscript is object oriented. Although you can sort of have this in JavaScript, Actionscript allows for object inheritance, etc.