I think _self may be a good bet. That's as far as I'm willing to go.
Window open() Method
Definition and Usage
The open() method opens a new browser window.
URL Optional. Specifies the URL of the page to open. If no URL is specified, a new window with about:blank is opened
name Optional. Specifies the target attribute or the name of the window. The following values are supported:
_blank - URL is loaded into a new window. This is default
_parent - URL is loaded into the parent frame
_self - URL replaces the current page
_top - URL replaces any framesets that may be loaded
name - The name of the window