This example draws a red circle when the clicked point falls outside of the specified polygon (the Bermuda Triangle), and a blue triangle when the click falls inside the polygon.
Read the documentation.
Git and Node.js are required to run this sample locally. Follow these instructions to install Node.js and NPM. The following commands clone, install dependencies and start the sample application.
git clone -b sample-poly-containsLocation https://github.com/googlemaps/js-samples.git
Other samples can be tried by switching to any branch beginning with
git checkout sample-SAMPLE_NAME