HTML5 Loading

Two questions.

At the moment my browser just shows 1% - 2% - 3%… 99% then the game shows up. Can I change this to show something else other than how much % is loaded?

Also, I have made a game which generates a map and it takes several seconds to generate the entire map. I get warned that a script is taking too long to run while this is happening. Is there a way to make this not happen?

The map is generated in some while loops like this:
at the beginning of the scene
while loop

I also tried doing
mapgen = 1
while(mapgen = 1)
mapgen = 0

That also gives the same warning about a script taking too long to run.