I wonder if you can set me straight on some javascript I'm a little confused with. The code is over here: http://jsfiddle.net/Lbd5k5zh/. The piece of code that escapes me is:
[...]
// Locate this entity at the given position on the grid
at: function(x, y) {
if (x === undefined && y === undefined) {
return { x: this.x/Game.map_grid.tile.width, y: this.y/Game.map_grid.tile.height }
} else {...}
}
If I'm in a nested loop for instance:
for(x=0;x<24;x++):
for(y=0;y<16;y++)
so x,y are clearly well defined and generating cartesian co-ords like thus:
(0,0) (1,0) (2,0)... (23,0)
(0,1) (1,1) (2,1)... (23,1)
(0,2) (1,2) (2,2) .
. . .
. . .
. . .
(0,14)(1,14)(2,14)
(0,15)(1,15)(2,15)...(23,15)
How will x or y ever become undefined? Moreover, I don't see where/how
return { x: this.x/Game.map_grid.tile.width === this.x/16
this.x becomes initialised? I realise it's an edge case but struggle to come up with a scenario where it may be used.
The point of checking if the arguments are undefined is do give 2 different behaviors (APIs) to the function.
If you call obj.at() (no arguments, i.e the body of the function will see the arguments as undefined), this function acts as a getter: it returns current coordinates.
If you call obj.at(x,y), this function acts more as a setter (sets the current position), from what I have seen. This is the case of the code in your post.
Whether designing functions API that way is good practice or not is debatable; your confusion is an argument in favor of the no.