Nunjucks 2.3.0 + Express 4.13.4

app.js

var nunjucks = require('nunjucks')
,   express  = require('express')
,   app      = express()
,   env
;

// view engine setup
app.set('views', path.join(__dirname, 'views'));

env = new nunjucks.Environment(
    new nunjucks.FileSystemLoader(app.get('views'))
,   { autoescape: true }
);

// add filters to env example
env.addFilter('asset', function(assetpath) {
    var asset_url = "path/to/assets/";
    return asset_url + assetpath; 
    return assetpath;
});
env.express(app);
app.set('view engine', 'nunjs'); // lets make our extension shorter.