The window.postMessage method is an asynchronous function that allows communication between different windows or iframes in a web page. It uses the publish-subscribe pattern, where one window posts a message, and other windows or iframes can listen for that message and respond accordingly.

However, window.postMessage does not provide a built-in mechanism for waiting for a response before code execution. It simply sends a message and continues with the next line of code. Therefore, you need to implement your own custom mechanism for waiting for a response.

One approach is to use a promise-based pattern. Here's an example:

// Sender window const sendMessageAndWaitForResponse = (message) => { return new Promise((resolve) => { // Add an event listener to listen for the response message window.addEventListener('message', function handler(event) { if ( === 'response') { // Remove the event listener window.removeEventListener('message', handler); // Resolve the promise with the response resolve(; } }); // Send the message using window.postMessage window.postMessage(message, '*'); }); }; // Receiver window window.addEventListener('message', (event) => { if ( === 'request') { // Handle the request and send the response window.postMessage('response', '*'); } });

In this example, the sender window uses window.postMessage to send a message to the receiver window and returns a promise that resolves when the receiver window responds with a specific message ('response' in this case). The receiver window listens for the request message ('request' in this case) using window.addEventListener, and when it receives the request, it sends the response using window.postMessage.

Please note that the use of '*' as the target origin in window.postMessage is insecure as it allows any window to receive the message. In a production environment, you should specify the target origin explicitly for security reasons.

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