This is functionally similar to assigning a new value to the window.location.href property. Because it is only available in MSIE you should avoid using this in cross-browser development.
Because this is only supported in MSIE, you should not use it if you want to develop portable scripts. A more portable technique is to assign the URL value to the href property of the location object that is accessible from the window.location property.
window.navigate("index.html"); and window.location.href = "index.html"; are functionally equivalent and guaranteed to be portable between Netscape Navigator and MSIE if not across all available browsers.