In JavaScript, there is no direct equivalent of dyn_cast() like in C++ for downcasting objects. However, you can achieve similar behavior by checking an object's prototype chain or using the instanceof operator to determine its type.

When you create a new window with, the new window becomes a separate global context, and objects in the parent window's global scope are not directly accessible in the child window. If you want to communicate or share data between the parent and child windows, you can use techniques like postMessage or shared data via window.opener.

Here's an example of how you can check the type of an object in the child window created with

Parent window:

<!DOCTYPE html> <html> <head> <title>Parent Window</title> </head> <body> <button id="openWindow">Open Child Window</button> <script> document.getElementById('openWindow').addEventListener('click', () => { const childWindow ='child.html', '_blank', 'width=300,height=200'); childWindow.myData = { value: 42 }; }); </script> </body> </html>

Child window (child.html):

<!DOCTYPE html> <html> <head> <title>Child Window</title> </head> <body> <script> const myData = window.myData; if (myData instanceof Object) { console.log('myData is an object:', myData); } else { console.log('myData is not an object.'); } </script> </body> </html>

In this example, when you click the "Open Child Window" button in the parent window, a new child window is opened with child.html. The parent window sets the myData property on the child window, and the child window accesses it using window.myData. The child window then checks the type of myData using instanceof Object to verify that it is an object.

Remember that in a real-world scenario, you might need to handle cases where the child window is not yet fully loaded before accessing the properties or using event listeners like load to ensure proper communication between windows.

As mentioned earlier, downcasting is not directly applicable in JavaScript, and the approach may vary depending on your use case. Be cautious when sharing data between different windows and make sure to handle security and privacy concerns accordingly.

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