setVisibleLayers(ids, doNotRefresh?)
Sets the visible layers of the exported map. By default, the visible layers are as defined by the default visibility in LayerInfo. 
To display no visible layers specify an array with a value of -1.

if(visible.length === 0){
  visible.push(-1);
}
layer.setVisibleLayers(visible);

 1 function getVisibleLayers(layer, subLayerIndex) {
 2     require(["dojo/_base/array"],function(array) {
 3         var layerInfos = layer.layerInfos;
 4         var i;
 5         // array for setting visible layers
 6         var visibleLayers = [-1];
 7 
 8         if (typeof subLayerIndex !== "undefined") {
 9             var newVis = !layerInfos[subLayerIndex].defaultVisibility;
10             // reverse current visibility of sublayer
11             layerInfos[subLayerIndex].defaultVisibility = newVis;
12         }
13 
14         // for each sublayer
15         for (i = 0; i < layerInfos.length; i++) {
16             var info = layerInfos[i];
17             // push to visible layers if it's visible
18             if (info.defaultVisibility) {
19                 visibleLayers.push(info.id);
20                 var negative = array.lastIndexOf(visibleLayers, -1);
21                 if (negative !== -1) {
22                     visibleLayers.splice(negative, 1);
23                 }
24             }
25         }
26         //Now that the array of visibleLayer Ids is assembled,说明：此处即是对GroupLayer进行处理
27         //strip off Ids of invisible child layers, and
28         //Ids of group layers (group layer Ids should not be submitted
29         //in .setVisible() or loss of toggle control madness ensues.
30         //Remove layers whos parents are not visible:
31         var noInvisibleParents = [];
32         for (i = 0; i < visibleLayers.length; i++) {
33             var id = visibleLayers[i];
34             var hasParentsInVisibleArray = this._allIdsPresent(layer, id, visibleLayers);
35             if (hasParentsInVisibleArray) {
36                 noInvisibleParents.push(id);
37             }
38         }
39         var noGroups = [];
40         for (var j = 0; j < noInvisibleParents.length; j++) {
41             var lyrInfo = this._getLayerInfo(layer, noInvisibleParents[j]);
42             if (lyrInfo && lyrInfo.subLayerIds === null) {
43                 noGroups.push(noInvisibleParents[j]);
44             }
45         }
46         // note: set -1 if array is empty.
47         if (!noGroups.length) {
48             noGroups = [-1];
49         }
50         return noGroups;
51     });
52 }