Syntax: How to Toggle Layer Visibility
IbComposer_toggleLayer(mapId,layerName);

where:

mapId

Alphanumeric

Is the unique identifier of the map control. For example, mapcontrol1.

layerName

Alphanumeric

Is the unique identifier of a layer within the map. For example, Layer1.
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Example: Toggling Layer Visibility
 
function button1_onclick(event) {
   var eventObject = event ? event : window.event;
   var ctrl = eventObject.target ? eventObject.target :
   eventObject.srcElement;
   // TODO: Add your event handler code here
   IbComposer_toggleLayer('mapcontrol1','Customers');
}