JavaScript: Checking if the current window is a popup

Introduction

In web development, managing window behavior is crucial for improving user experience and for certain functionalities. One common scenario is determining whether the current window is a popup. A popup window is usually a smaller window created for a specific task or to display additional information without navigating away from the current page. In this tutorial, we’ll explore how to use JavaScript to check if the current window is a popup.

Understanding the context in which your JavaScript code is running can greatly affect its behavior and your approach to handling that behavior. Particularly, differentiating between a normal browser window and a popup window can influence how you display content, prompt user interactions, and manage the window size.

What Defines a Popup Window?

Before diving into the code, let’s clarify what qualifies as a popup window. A popup window can be defined by its characteristics or how it was opened:

• Size: Popups are typically smaller than the full browser window.
• Features: They may have limited browser controls (e.g., no address bar, limited navigation buttons).
• Method of Opening: Often opened by JavaScript’s window.open() method or through HTML with specific attributes set to create a more focused experience.

Keeping these characteristics in mind, let’s explore how to identify popup windows using JavaScript.

Using Window Properties

JavaScript provides several properties of the window object that can help determine if the current window is a popup. Let’s look at some practical examples.

Example 1: Checking Window Size

if (window.outerWidth < 600 && window.outerHeight < 600) {
  console.log('This is likely a popup window based on its size.');
}

This approach assumes that popup windows are smaller and checks the size of the window. It’s a simple but not foolproof method, as not all popups are strictly defined by their size, and users can manually resize windows.

Example 2: Examining the Window’s Features

const features = 'menubar=no,location=no,resizable=yes,scrollbars=yes,status=no';

function openPopup(url) {
  window.open(url, 'popupWindow', features);
}

function isPopup() {
  return window.opener && window.features.includes('menubar=no');
}

This snippet demonstrates opening a popup with certain features disabled (e.g., menubar, location bar) and then checking if the current window was opened with those features. It’s important to note that this method is reliant on maintaining a consistent setup for your popups, as checking against specific features string might not be reliable if the popup’s features vary greatly.

Example 3: Using window.opener

if (window.opener && !window.opener.closed) {
  console.log('This window was opened by another window, potentially a popup.');
}

This method leverages the window.opener property, which references the window that opened the current window, if any. A non-null window.opener suggests that the current window could be a popup, especially if it was opened via a script in another window. This method is relatively reliable for detecting if the window was programmatically opened by another page.

Advanced Detection: Query Strings and Post Messages

If the aforementioned methods don’t meet your needs for reliability or specificity, consider using a combination of query strings and the window.postMessage API for more advanced control.

Passing Information Through Query Strings

function openPopup(url) {
  const popupUrl = `${url}?isPopup=true`;
  window.open(popupUrl, 'popupName');
}

function checkForPopup() {
  const params = new URLSearchParams(window.location.search);
  if (params.get('isPopup') === 'true') {
    console.log('This window is a popup.');
  }
}

By appending a query string parameter when opening a popup, you can easily check this parameter in the child window to determine if it’s a popup. This method offers clarity and control, allowing you to pass and check for specific parameters intentionally marked at the point of creation.

Communication via window.postMessage

For an even more direct approach, using the window.postMessage API serves as a secure way to perform cross-origin communication between your windows.

const popup = window.open(url);
popup.postMessage({ type: 'identify', text: 'Are you a popup?' }, '*');

window.addEventListener('message', (event) => {
  if (event.data.type === 'identify' && event.data.text === 'Yes, I am a popup') {
    console.log('Confirmed: This window is a popup.');
  }
});

This method requires handling messages in both the opener and the opened windows, facilitating an explicit confirmation of the window’s nature directly from the source. It’s efficient for modern web applications where cross-window or cross-origin communication is common.

Conclusion

Determining whether the current window is a popup can be approached in several ways, each with its benefits and drawbacks. Developers should choose the method that best fits their application’s needs and the level of certainty required. Employing a mix of strategies may provide the most accurate detection, ensuring a smooth and intuitive user experience across your web applications.