Removing Layer on ArcGIS API For JavaScript>

I am adding a markers layer called layer1 like this to map

function drawPoints(mapInfo) {
  layer1 = new esri.layers.GraphicsLayer();
    for (var i = 0; i < mapInfo.length; i++) {
           var projects = mapInfo[i];
           var project = new esri.geometry.Point(projects.Longitude, projects.Latitude);
           project = esri.geometry.geographicToWebMercator(project);
           var symbol = new esri.symbol.PictureMarkerSymbol("img/map/marker.png", 18, 18);
           projectInfoTemplate = new InfoTemplate();
           projectInfoTemplate.setTitle("Project Details");
           projectInfoTemplate.setContent('<div class="row"></div> ');
           var projectsG = new esri.Graphic(project, symbol).setInfoTemplate(projectInfoTemplate);
           layer1.add(projectsG);
           }
          map.addLayer(layer1);
 }

now in next request I need to clear map so I used the

map.removeLayer(layer1);

but this is causing error because the layer1 still not created at first request. Now I need to check IF the map has a layer called layer1 then removeit. Here is a pseudo code of what I need to do:

if(map.has/contains/include(layer1){
  map.removeLayer(layer1);
}

can you please let me know how to do that?