Function Prototype help

What does prototyping a function do?

i got this from the tile based games site.
//////////////////////////////////////////////////
game.Tile0 = function () { };
game.Tile0.prototype.walkable = true;
game.Tile0.prototype.frame = 1;

game.Tile1 = function () { };
game.Tile1.prototype.walkable = false;
game.Tile1.prototype.frame = 2;
/////////////////////////////////////////////////
game[name] = new game"Tile"+map*[j];
/////////////////////////////////////////////////

Can anyone explain prototyping?

A before hand thanks~

http://www.kirupa.com/developer/oop/AS1OOPIntro.htm :thumb: