just for a while & just awhile

just for a while：哪怕只是一会儿.不能等同于 just a moment.
例如：Can you concentrate on the speech just for a while?
just awhile：我感觉应该是 just a while 吧,有 just a moment 的意思,也有 just for a while 的意思.
等同于just a moment就不用说了,等同于just for a while的时候,例如：Wait a while,wait just a while.等一会儿,再等一会儿.