Can you count unique visitors to a website without server side code?

I have created a Gatsby blog for my friend, which means it is serverless and does not use a database. This works quite well for a blog which will only need builds every time I make changes or he adds a blog post - however it wouldn't work too well for tracking unique user visits as it would have to do too many builds if many people visited within a short time span.

Is there a way I can track unique user visits without a database involved?

Like it has been said, you need a third-party tool (like Google Analytics) since any workaround done in the front-end part will be related to the client/browser-side, then you'll lose the tracking if a user changes the device for example.

You can easily install Analytics with some of the available plugins (like gatsby-plugin-google-gtag). This is recommended since under the hood uses gtag.js instead of analytics.js, which is what Google recommends due the last API changes.

To use is just install it by:

npm install gatsby-plugin-google-gtag // or yarn add gatsby-plugin-google-gtag

And add your configurations:

// In your gatsby-config.js
module.exports = {
  plugins: [
    {
      resolve: `gatsby-plugin-google-gtag`,
      options: {
        // You can add multiple tracking ids and a pageview event will be fired for all of them.
        trackingIds: [
          "GA-TRACKING_ID", // Google Analytics / GA
        ],
        // This object gets passed directly to the gtag config command
        // This config will be shared across all trackingIds
        gtagConfig: {
          optimize_id: "OPT_CONTAINER_ID",
          anonymize_ip: true,
          cookie_expires: 0,
        },
        // This object is used for configuration specific to this plugin
        pluginConfig: {
          // Puts tracking script in the head instead of the body
          head: false,
          // Setting this parameter is also optional
          respectDNT: true,
          // Avoids sending pageview hits from custom paths
          exclude: ["/preview/**", "/do-not-track/me/too/"],
        },
      },
    },
  ],
}

You can ignore the options you don't need.