Google Tag Manager tag load GeoIP data into data layer from ipapi.co. Provides the data necessary to help with GDPR.

gtm-ipapi-tag.html

<script>

	/*
	 * get geographical location data by ip address
	 * uses the free ipify.org service
	 * and the paid ipapi.co service
	 * and intelligent caching to minimize requests
	 */

	// mark the start of the script loading
	window.dataLayer = window.dataLayer || [];
	window.dataLayer.push({
		"event": "geoip.js",
		"geoip.start": (new Date()).getTime()
	});

	(function () {

		"use strict";

		var isGeoIPLoaded, isWindowLoaded;

		function onWindowLoadAndGeoIPLoad () {

			if (isGeoIPLoaded && isWindowLoaded) {

				// push location data into GTM data layer
				// use this event to trigger third-party scripts after first-party scripts and know the geo data is available
				window.dataLayer.push({
					"event": "geoip.window.load"
				});

			}

		}

		window.addEventListener("load", function onWindowLoad () {

			isWindowLoaded = true;
			onWindowLoadAndGeoIPLoad();

		});

		// helper function to push data to data layer
		function onSuccess (data, doNotSaveData) {

			// push location data into GTM data layer
			window.dataLayer.push({
				"event": "geoip.load",
				"geoip.data": data
			});
			isGeoIPLoaded = true;
			onWindowLoadAndGeoIPLoad();

			if (!doNotSaveData) {

				// store data in local storage
				if (data && data.ip) {

					var key = "ipapi.data." + data.ip;
					localStorage.setItem(key, JSON.stringify(data));

				}

			}

		}

		// helper function to log and throw error
		function onError (err) {

			throw new Error(err.code + ": " + err.error);

		}

		// helper function to execute once we have the IP address
		function onIPLoaded (ip) {

			var data, key, request;

			window.dataLayer.push({
				"event": "geoip.ip",
				"geoip.ip": ip
			});

			// check local storage for geoip data for that IP address
			key = "ipapi.data." + ip;
			data = localStorage.getItem(key);
			if (data) {

				// GeoIP data found in local storage
				try {
					data = JSON.parse(data);
					onSuccess(data, true);
				} catch (err) {
					throw err;
				}

			} else {

				// fetch GeoIP data from ipapi.co

				request = new XMLHttpRequest();
				request.open("GET", "https://ipapi.co/" + ip + "/json/", true);
				request.onload = function () {

					if (this.status >= 200 && this.status < 400) {

						// Success!
						data = JSON.parse(this.response);
						onSuccess(data);

					} else {

						onError(new Error("Unexpected HTTP Status Code " + this.status));

					}

				};
				request.onerror = onError;
				request.send();

			}

		}

		var ip = sessionStorage.getItem("ipify.ip");
		if (ip) {

			// use IP address retrieved from session cache
			onIPLoaded(ip);

		} else {

			// use ipify.org to get IP address
			// listen for when the IP address has been loaded by ipfiy
			window.ipifyCallback = function ipifyCallback (json) {

				sessionStorage.setItem("ipify.ip", json.ip);
				onIPLoaded(json.ip);

			};

			// inject the script from ipify.org
			var newNode, referenceNode;

			referenceNode = document.getElementsByTagName("script")[0];
			newNode = document.createElement("script");
			newNode.async = true;
			newNode.src = "https://api.ipify.org?format=jsonp&callback=ipifyCallback";
			referenceNode.parentNode.insertBefore(newNode, referenceNode);

		}

	}());

</script>