render with one loop

world.js

    function drawMap(map) {
        var x, y,
            width = map[0].length,
            current_node = map.length * width;
        while (current_node--) {
            x = current_node % width;
            y = ~~(current_node / width);
            drawTile({
                x: x,
                y: y
            }, {
                top:    map[y-1][x-1],
                right:  map[y-1][x],
                bottom: map[y][x],
                left:   map[y][x-1]
            });
        }
    }