Specifying Multiple Targetorigin Uris In Postmessage

PostMessage is a powerful method in JavaScript that allows communication between different windows or iframes. It's commonly used in web applications to enable cross-origin communication. When working with PostMessage, specifying the targetOrigin is crucial for security reasons. This restriction ensures that messages are only sent to specific origins, preventing malicious attacks.

While the targetOrigin parameter is essential, specifying multiple URIs for targetOrigin might be necessary in certain situations. This can be particularly useful when your web application interacts with multiple origins and you need to control which origins are allowed to receive the messages.

To specify multiple targetOrigin URIs in PostMessage, you can use an array to define the allowed origins. Here's a step-by-step guide on how to achieve this:

1. Define an Array of Allowed Origins:

const allowedOrigins = ['https://example1.com', 'https://example2.com', 'https://example3.com'];

2. Check the Origin Before Sending Messages:
Before sending a message using PostMessage, verify whether the target origin is included in the allowedOrigins array. This step is crucial for ensuring that messages are only sent to the specified origins. Here's an example code snippet demonstrating this:

const targetOrigin = 'https://example2.com'; // Specify the target origin
if (allowedOrigins.includes(targetOrigin)) {
  // Send the message to the specified origin
  window.postMessage('Hello, world!', targetOrigin);
} else {
  console.error('Target origin is not allowed.');
}

3. Handling Messages from Multiple Origins:
On the receiving end, you can verify the origin of the incoming message by checking the event.origin property. By comparing the event origin with the allowedOrigins array, you can ensure that messages are accepted only from the specified origins. Here's an example code snippet:

window.addEventListener('message', event => {
  if (allowedOrigins.includes(event.origin)) {
    // Process the incoming message from the allowed origin
    console.log('Message received:', event.data);
  } else {
    console.error('Message rejected due to invalid origin:', event.origin);
  }
});

By following these steps, you can securely specify multiple targetOrigin URIs in PostMessage, enhancing the security of your web application. Remember to update the allowedOrigins array whenever necessary to accommodate changes in your application's communication requirements.

In summary, controlling the target origins in PostMessage is essential for maintaining the security and integrity of your web application. By specifying multiple targetOrigin URIs, you can ensure that messages are exchanged only with the intended origins, enhancing the overall security of your web application.