Cesium.js zoom to camera

zoom.js

var eventHandler, mousePosition;

viewer.scene.screenSpaceCameraController.enableZoom = false;
eventHandler = new ScreenSpaceEventHandler(viewer.scene.canvas);

eventHandler.setInputAction(function (event) {
    mousePosition = event.endPosition;
}, ScreenSpaceEventType.MOUSE_MOVE);

eventHandler.setInputAction(function (wheelZoomAmount) {
    var cameraHeight, directionToZoom, zoomAmount;
    if (mousePosition) {
        cameraHeight = viewer.scene.globe.ellipsoid.cartesianToCartographic(viewer.camera.position).height || Number.MAX_VALUE;
        directionToZoom = viewer.camera.getPickRay(mousePosition).direction;
        zoomAmount = wheelZoomAmount * cameraHeight / 1000;

        viewer.camera.move(directionToZoom, zoomAmount);
    }
}, ScreenSpaceEventType.WHEEL);