from https://dev.opera.com/articles/efficient-javascript
Occasionally, it is necessary to change the page address using a script. The typical way to do this is by assigning a new address to location.href. This adds a history entry, and loads a new page, in the same way as activating a normal link.
In some cases, this extra history entry is unwanted, as the user will not need to go back to the earlier page. This is particularly useful if working in a situation where memory usage is critical. The memory used by the current page can be recovered by replacing the history entry instead. This is done using thelocation.replace() method.
location.replace('newpage.html');
Note that the page may still remain in cache, and may use memory there, but this will not be quite so much as if it were also kept in history.