browser.saveHistory() - TypeError: undefined is not a function

[Abbid]

Hi,

New to ZombieJs.
Im getting this error when i try to save the browser history and storage (i want to save the browser state between requests into a session).
Any idea why? or is there another way to save the browser between requests?
Below is the code i'm using. Any help would be greatly appreciated.

browser.visit(start_url)
.then(function(something){
console.log('processing...');
var history = browser.saveHistory();
res.send('finished');
});