What are the differences of these three static url?
I am not sure if I am right, I am using the MEDIA_ROOT to store my uploaded photos (via models.ImageField()) 
However, I created a JS script to my admin and in admin.py. I defined the media as below:
....
class Media:
      js = ('/admin/custom.js', )
and my settings.py:
 ....
 STATIC_ROOT = "/home/user/project/django1/top/listing/static"
and I added the custom.js to STATIC_ROOT/admin/custom.js, but it is not working. Throwing 404 not found error. 
And then I change the STATIC_ROOT to STATICFILES_DIRS, and it works!!
....
STATICFILES_DIRS = "/home/user/project/django1/top/listing/static"
So, I am not understand what is going on here. In fact, I just don't understand what is the difference between STATIC_ROOT and STATICFILES_DIRS. 
Currently I am testing Django in my machine via virtualenv, not deployed yet, is it the reason STATIC_ROOT not working?? 
 
     
     
     
     
    