How can I find if the given lat and lng is inside a particular circular area in Google maps.

The below code is for creating a circular area in lat: 41.878, lng: -87.629 , with a radius of 500.

const citymap = {
  chicago: {
    center: { lat: 41.878, lng: -87.629 },
    population: 2714856,
  },
};

function initMap() {
  // Create the map.
  const map = new google.maps.Map(document.getElementById("map"), {
    zoom: 15,
    center: { lat: 41.878, lng: -87.629 },
    mapTypeId: "terrain",
  });

  // Construct the circle for each value in citymap.
  for (const city in citymap) {
    // Add the circle for this city to the map.
    const cityCircle = new google.maps.Circle({
      strokeColor: "#FF0000",
      strokeOpacity: 0.8,
      strokeWeight: 2,
      fillColor: "#FF0000",
      fillOpacity: 0.35,
      map,
      center: citymap[city].center,
      radius: 500,
    });
  }
}

Now I have a user location, How can I find the user is inside the circle or not?

const userLocation = { lat: 51.878, lng: -77.629 }

function isUserInsideCircle(userLocation){
  // check user inside circle or not
}

fiddle sample - https://jsfiddle.net/bmt4ruon/