What is the difference between setting a property on app.locals and calling app.set()?

Question

I'm in the process of learning Express - and thinking of the best place to save config style data. Options available are either in app.locals or app.set (settings)... so:

app.locals({ config: {     name: 'My App',     domain: 'myapp.com',     viewPath: __dirname+'/views',     viewEngine: 'jade'     port: 3000 } });  app.set('view engine', app.locals.config.viewEngine || 'jade'); 

This would also allow me to use the following in my views:

<title>#{config.name}</title> // <title>My App</title> 

Or the alternative is to use app.set like so:

app.set('name', 'My App'); app.set('domain', 'myapp.com'); 

... and then use this in the view:

<title>#{settings.name}</title> 

I know both methods work, but I'm struggling to determine which is the better method to use. At the moment I'm leaning towards using app.locals, with the extra 'app' namespace as I believe there would be less chance of conflicts with future updates and other modules if using app.set.

Answer 1

Wow, all of the answers are wrong, so let me give it a try. Despite what others say assinging to the app.local argument is different from using app.set(). Watch,

app.js   app.locals.foo = 'bar';   app.set('baz', 'quz');     index.jade   block content                                 dl                                            dt app.locals.foo = 'bar';                   dd \#{settings.foo} = #{settings.foo}       dd \#{foo} = #{foo}                          dt app.set('baz', 'quz')                    dd \#{settings.baz} = #{settings.baz}       dd \#{baz} = #{baz} 

If you ran this code, what you would see is,

app.locals.foo = 'bar';   #{settings.foo} =   #{foo} = bar app.set('baz', 'quz')   #{settings.baz} = quz   #{baz} = 

The reason for this is setting app.locals sets attributes of the object that the view uses as its environment; what the view will read from without qualification. Conversely, app.set sets attributes on app.locals.settings. You can verify this if you clobber app.locals.settings in the above with app.locals.settings = {}, which will make #{settings.baz} undefined.

So which do you use? If it's not an app setting based on the response (res.set) or global configuration (app.set), use the direct write to app.locals.

Answer 2

All properties of app.locals are available in templates. Using app.set assigns properties to app.locals.settings, which is used for global application settings and is inherited by mounted applications. For example:

var app1 = express(),     app2 = express();  app1.set('inheritable', 'foo'); app1.locals.notInheritable = 'bar';  app1.use('/mount', app2);  app2.get('inheritable') === 'foo'; // true app2.locals.notInheritable === 'bar'; // false 

So it's really a question of preference and whether or not you're mounting applications.