var screenPt = evt.screenPoint;
var mapPt = map.toMap(screenPt);
if (Math.abs(screenPt.x - 335) < 55) {
if(screenPt.x < 335) {
screenPt.x = 270;
} else {
screenPt.x = 400;
}
}
var mapPtNew = map.toMap(screenPt);
shiftX = mapPt.x - mapPtNew.x;
map.setExtent(map.extent.offset(shiftX, 0));