I have an array which is part of a small JS game I am working on I need to check (as often as reasonable) that each of the elements in the array haven't left the "stage" or "playground", so I can remove them and save the script load

I have coded the below and was wondering if anyone knew a faster/more efficient way to calculate this. This is run every 50ms (it deals with the movement).

Where bots[i][1] is movement in X and bots[i][2] is movement in Y (mutually exclusive).

for (var i in bots) {
    var left = parseInt($("#" + i).css("left"));
    var top = parseInt($("#" + i).css("top"));
    var nextleft = left + bots[i][1];
    var nexttop = top + bots[i][2];
    if(bots[i][1]>0&&nextleft>=PLAYGROUND_WIDTH) { remove_bot(i); }
    else if(bots[i][1]<0&&nextleft<=-GRID_SIZE) { remove_bot(i); }
    else if(bots[i][2]>0&&nexttop>=PLAYGROUND_HEIGHT) { remove_bot(i); }
    else if(bots[i][2]<0&&nexttop<=-GRID_SIZE) { remove_bot(i); }
    else {
        //alert(nextleft + ":" + nexttop);
        $("#" + i).css("left", ""+(nextleft)+"px");
        $("#" + i).css("top", ""+(nexttop)+"px");
    }
}

On a similar note the remove_bot(i); function is as below, is this correct (I can't splice as it changes all the ID's of the elements in the array.

function remove_bot(i) {
    $("#" + i).remove();
    bots[i] = false;
}

Many thanks for any advice given!