How to fix the "Loading the Google Maps JavaScript API without a callback is not supported" error

Kris Lachance

Head of Growth

When integrating the Google Maps JavaScript API, it's important to adhere to specific loading strategies mandated by the API. The error message "Loading the Google Maps JavaScript API without a callback is not supported" suggests that your implementation is attempting to load the API without specifying a callback function, which is required for asynchronous loading.

Analyze the script tag for the Google Maps JavaScript API

The first step in troubleshooting this issue is to inspect the script tag where the Google Maps API is included. Ensure that the src attribute of the script tag includes the callback parameter with a valid function name that will be called once the API is loaded.

<script src="<https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY&callback=initMap>" async defer></script>

Replace YOUR_API_KEY with your actual API key and initMap with the name of the callback function you intend to use.

Define the callback function in your JavaScript

Ensure that the callback function specified in the script tag's callback parameter is defined in your JavaScript. This function will execute when the API has fully loaded.

function initMap() {
  // Your code to initialize the map goes here
}

Confirm the order of script execution

Your callback function must be defined before the Google Maps script attempts to call it. If the script is loaded asynchronously, it's crucial to have the callback function available, or else you'll encounter the error.

<script>
function initMap() {
  // Initialization code here
}
</script>
<script src="<https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY&callback=initMap>" async defer></script>

Check for async and defer attributes

The async or defer attributes in the script tag ensure that the loading of the API does not block the rendering of the page. The use of async implies that the script will be executed as soon as it is loaded, while defer will execute the script after the document has been parsed. Either attribute necessitates the use of a callback.

<script src="<https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY&callback=initMap>" async></script>

<script src="<https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY&callback=initMap>" defer></script>

Verify no multiple API loads

Loading the Google Maps JavaScript API multiple times on the same page can lead to conflicts and the aforementioned error. Scan your HTML to make sure the API is included only once.

Use error handling

Include error handling within your callback function to catch any issues that arise during the initialization of the map.

function initMap() {
  try {
    // Map initialization code
  } catch (error) {
    console.error("Map initialization error:", error);
  }
}

Update the API key permissions

Sometimes, the issue may not be with the callback, but with the API key itself. Ensure that your API key is correctly configured in the Google Cloud Console, has Maps JavaScript API enabled, and the correct application restrictions (like HTTP referrers) are set.

Testing in isolation

If the issue persists, isolate the API loading script in a simple HTML file to rule out conflicts with other scripts or libraries.

<!DOCTYPE html>
<html>
<head>
  <title>Simple Map</title>
</head>
<body>
  <div id="map" style="height: 400px; width: 100%;"></div>
  <script>
  function initMap() {
    // Initialization code here
  }
  </script>
  <script src="<https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY&callback=initMap>" async defer></script>
</body>
</html>

Replace YOUR_API_KEY with your actual API key and include your map initialization code in initMap.

By following these steps, you should be able to resolve the "Loading the Google Maps JavaScript API without a callback is not supported" error, ensuring that your map loads correctly and efficiently. If the problem persists after these checks, consulting the Google Maps JavaScript API documentation or reaching out to the Google support forums may provide additional insights.

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