I searched and got this answer
http://forums.mozillazine.org/viewtopic.php?f=25&t=185201&start=0&st=0&sk=t&sd=a
Actually, neither of them are 'official.' Just that 'application/x-javascript' is proper because the 'x-' explicity states that it <i>isn't</i> official.
So what should I use?
type='text/javascript', type='application/x-javascript' or type='application/javascript'?
Many javascript books use 'text/javascript' and I think 'text/javascript' is used in most cases. Even people claim that type='application/x-javascript' is more proper, they also said that due to 'text/javascript' and supported by most browsers, so 'text/javascript' should be used.
But I think most current versions browsers support type='application/x-javascript' now. I may use type='application/x-javascript' from now on, is it a right approach?