To open only one instance of a popup window in an HTML page, use the windowName parameter of the window.open method.
For example window.open(‘http://www.devx.com’) will open a new window each time the user clicks the link containing the window.open code. In constrast, window.open(‘http://www.devx.com’,’devx’) will open only one instance of the window, no matter how many times users click the link.