side by side map compare

i want to compare 3/4 maps side by side in cesium like this:

I know how to show many viewers but i don’t know how to synchronize it like in this example.
Can someone help me? This is what i try but the views are not sychronized.

(*remove "fullsize to see the 2. viwer)
var viewer = new Cesium.Viewer(‘cesiumContainer’);
var viewer2 = new Cesium.Viewer(‘cesiumContainer2’);
var masterCamera =; var slaveCamera =; viewer2.scene.preRender.addEventListener(function() { if (viewer2.scene.mode !== Cesium.SceneMode.MORPHING) { slaveCamera.setView({ position : masterCamera.position, heading : masterCamera.heading, pitch : masterCamera.pitch, roll : masterCamera.roll }); } });