Web on page 287 of the PHB says (emphasis mine):
You conjure a mass of thick, sticky webbing at a point of your choice within range. The webs fill a 20-foot cube from that point for the duration. The webs are difficult terrain and lightly obscure their area.
As the area is lightly obscured it would seem likely that creatures can see through to the other side. Assuming that the creature can see the target on the other side of the web, do ranged physical or magical attacks pass through an area affected by the Web spell, or does the mass prevent it?