var viewer = new Cesium.Viewer('cesiumContainer');

// Create a typical CzmlDataSource.
var dataSource1 = new Cesium.CzmlDataSource();
dataSource1.load('../../SampleData/simple.czml');

// Add a checkbox at the top.
document.getElementById('toolbar').innerHTML =
    ' Show CZML';

var checkbox = document.getElementById('showCheckbox');
checkbox.addEventListener('change', function() {
    // Checkbox state changed.
    if (checkbox.checked) {
        // Show if not shown.
        if (!viewer.dataSources.contains(dataSource1)) {
            viewer.dataSources.add(dataSource1);
        }
    } else {
        // Hide if currently shown.
        if (viewer.dataSources.contains(dataSource1)) {
            viewer.dataSources.remove(dataSource1);
        }
    }
}, false);