// Define a LineString object.
var lineString = ee.Geometry.LineString([[-122.09, 37.42], [-122.08, 37.43]]);
// Apply the toGeoJSON method to the LineString object.
var lineStringToGeoJSON = lineString.toGeoJSON();
// Print the result to the console.
print('lineString.toGeoJSON(...) =', lineStringToGeoJSON);
// Display relevant geometries on the map.
Map.setCenter(-122.085, 37.422, 15);
Map.addLayer(lineString,
{'color': 'black'},
'Geometry [black]: lineString');