How do I update A Jade Template form an ajax post?

I have set up a basic node.js web-app using express with the default view engine jade.

When the User first loads the page the following occurs

app.get('/', function(req, res){
    res.render('index', {
        title: 'Test',
        mode: "user"
    });
});

What i cannot work out is how to then change the parameter I initially passed into the jade template from a ajax call.

app.post('/', function(req, res){
    console.log(req.body.list);
    res.redirect('back');
    // I imagine the code needs to go here and look somewhat like the following
    // 
    // res.?update-view({
    //  mode: "admin"
    // });
});

If anyone has had experience with this working your input would be appreciated.