So we already have isometric view and path finding topic behind us, now it is time for the third and final part: field of view. Basically it usually comes down to checking whether there is a direct connection between two points (for example a player character and an enemy), without anything blocking the line. More often than not, it is usually quite a complicated issue, but luckily not in tile-based engines -we just need a line drawing algorithm. Why is that? Line drawing algorithms start at one point and move toward another one pixel by pixel, until they form a line. Now if we were to replace the drawing function with one checking the tiles, the result would be an algorithm that step by step checks a line in between two points for some kind of obstacles.
That said, we first need an algorithm - personally I recommend one from Wikipedia: Bresenham Algorithm. Implemented in ActionScript it might look like this:

function isInSight(tiles:Vector.<Vector.<int>>,x1:Number, y1:Number, x2:Number, y2:Number):Boolean {
	var dx:Number;
	var dy:Number;
	if (x1>x2) {
		dy = y1;
		y1 = y2;
		y2 = dy;
		dx = x1;
		x1 = x2;
		x2 = dx;
	}
	dx = x2-x1;
	dy = y2 - y1;
			
	var y:Number;
	var x:Number;
	var m:Number;
	if (Math.abs(dx)>Math.abs(dy)) {
		m = dy/dx;
		y = y1;
		for (x=x1; x<x2; x++) {
			if(tiles[x][y] == 1) return false;
			y = y+m;
		}
	} else {
		m = dx/dy;
		x = x1;
		if (y1<y2) {
			for (y = y1; y < y2; y++) {
				if(tiles[x][y] == 1) return false;
				x = x+m;
			}
		} else {
			for (y = y1; y > y2; y--) {
				if(tiles[x][y] == 1) return false;
				x = x-m;
			}
		}
	}
	
	if(tiles[x2][y2] == 1) return false;
	return true;
}

The isInSight function will return false when on the way from point 1 to point 2 there will be a tile marked as 1 in two-dimensional array tiles.
Easy. And the best part is that most line drawing algorithms are quite fast making this solution viable even in really big maps.