Yes, you can pass a JavaScript variable from one browser window to another using various methods, such as cookies, query strings, local storage, and window.postMessage().

Here’s a brief overview of each method:

1. Cookies: You can set a cookie with the JavaScript variable in the first browser window and read the cookie in the second browser window.

2. Query strings: You can append the JavaScript variable as a query parameter to the URL of the second browser window and extract it from the query string in the second window.

3. Local storage: You can set the JavaScript variable in local storage in the first browser window and retrieve it from local storage in the second browser window.

4. window.postMessage(): This method allows you to securely send a message from one window to another, even if they have different origins (i.e., different domains). You can pass the JavaScript variable as the message payload and listen for the message event in the receiving window to extract the variable.

Here’s an example of how you can use the postMessage() method to pass a JavaScript variable from one browser window to another:

In the first browser window:

// Set the variable to be passed
const myVariable = "Hello from Window 1!";

// Send the variable to the second window
const secondWindow = window.open("https://example.com/second-window");
secondWindow.postMessage(myVariable, "https://example.com");

In the second browser window:

// Listen for the message event
window.addEventListener("message", event => {
  // Verify that the message is from a trusted source
  if (event.origin === "https://example.com") {
    // Extract the variable from the message payload
    const myVariable = event.data;
    console.log(myVariable); // Output: "Hello from Window 1!"
  }
});

In this example, the first window sets the JavaScript variable myVariable and sends it to the second window using the postMessage() method. The second window listens for the message event and verifies that it is from a trusted source before extracting the variable from the message payload.

Note that when using postMessage(), you should always verify that the message is from a trusted source to prevent security vulnerabilities.