Update main window DOM from other window


Let’s take a TODO app as example, there is a Main window , A, that will list all of the TODO items and a button ‘Add Item’. So when click on the ‘Add Item’ , it will open up a second window, B, where there is a form for adding item. After the form is submitted, the newly added item will be append to the list in WIndow A.

So the problem here is, how can I update the Item list in WIndow A when when WIndow B form is submitted?

Btw, I am using react js for renderer. How to make the react compenent listen to the change?