Express.js View "globals"

I'm using Express.js (on Node.js) and I know that you can render a view with custom data via the "locals" parameter. (res.render("template", { locals: { foo: "bar" } });)

Is there any way to have "globals"? (ie. data that's accessible to every view)

I saw view options, but that isn't recursive, so it replaces the locals I set if I use any locals with my template.

This is my use case: I want to make it so that CSS/JS files can be added on a per-page basis, and that is part of my main layout. The problem is, if I don't explicitly set those arrays on every render, I get an undefined error, so in my template I always have to do the typeof css !== "undefined" dance. Additionally, I have other select box option lists that I don't want to have to explicitly add to each of my forms.

It's worth noting for those who may have come across this question since the release of Express 3, that the method 'dynamicHelpers' no longer exists.

Instead you can use the app.locals function, which acts as an object you can store values or functions in, and then makes them available to views. For example:-

// In your app.js etc.
app.locals.title = "My App";
app.locals({
    version: 3,
    somefunction: function() {
        return "function result";
    }
});

// Then in your templates (shown here using a jade template)

=title
=version
=somefunction()  

// Will output

My App
3
function result

If you need access to the request object to pull information from, you can write a simple middle-ware function and use the app.settings variable.

For example, if you are using connect-flash to provide messages to your users, you might do something like this:

app.use(function(req, res, next) {
    app.set('error', req.flash('error'));
    next();
});

Which would give you access to the error message with =settings.error in your template.

These topics are covered here, albeit slightly briefly: http://expressjs.com/api.html#app.locals

Update: Express 4

app.locals is now a simple JavaScript Object, so every property has to be set one by one.

app.locals.version = 3;
app.locals.somefunction = function() {
    return "function result";
}

res.locals provides the exact same functionality, except it should be used for request-specific data rather than application-wide data. A user object or settings is a common use case.

res.locals.user = req.isAuthenticated() ? req.user : null;
res.locals.userSettings = {
    backgroundColor: 'fff'
}

There is a way to have "global" variables for views, using dynamic view helpers.

From the Express.js guide:

app.dynamicHelpers(obj)

Registers dynamic view helpers. Dynamic view helpers are simply functions which accept req, res, and are evaluated against the Server instance before a view is rendered. The return value of this function becomes the local variable it is associated with.

app.dynamicHelpers({ session: function(req, res){ return req.session; } });

All views would now have session available so that session data can be accessed via session.name etc:

You can find a real example on how to use them here: https://github.com/alessioalex/Nodetuts/tree/master/express_samples (node app.js to start the app)

A real-world example of using view options as the author mentioned:

var app = express.createServer();

app.configure(function() {
  app.set('views', path.join(__dirname, '..', 'views'));
  app.set('view engine', 'jade');
  app.set('view options', {
    assetVersion: 1
  });

And then in my layout.jade (base template for the app in my case):

link(rel='stylesheet', href='/static/css/' + assetVersion + '/style.css')
script(src='/static/js/' + assetVersion + '/script.js')

With this little trick, I only have to update the assetVersion variable one place to make sure that my assets aren’t cached in Varnish or other places.

I wound up looking into the source code, and I've actually found that this is now possible in never versions of Express. (so far, only available through GitHub)

The simplest way to accomplish this is to create a variable that represents the default set of locals for your views. Then create a function that accepts an object, merges it with the locals, and returns the merged object.

I also pass ALL my locals inside a container object i.e. {locals:{g:{prop:val}}} so in my views I can refernce g.prop which will just return null when it isn't set, instead of throwing an undefined error.

function default_page_vars(custom_vars){
    var vars = {
        footer: true,
        host: req.headers.host.split(':')[0],
        config: this.config
    };

    if(custom_vars){
        for(var k in custom_vars){
            vars[k] = custom_vars[k];
        }
    }
    return {
        g:vars
    };
}

//within your handler
response.render(view, {
    locals: default_page_vars(other_locals)
});