Express How to pass app-instance to routes from a different file

Question

I want to split up my routes into different files  where one file contains all routes and the other one the corresponding actions  I currently have a solution to achieve this  however I need to make the app-instance global to be able to access it in the actions  My current setup looks like this   app js   var express     require  express    var app         express createServer    var routes      require    routes     var controllers   require    controllers    routes setup app  controllers    app listen 3000  function       console log  Application is listening on port 3000          routes js   exports setup   function app  controllers       app get      controllers index     app get   posts   controllers posts index     app get   posts  post   controllers posts show        etc        controllers index js   exports posts   require    posts     exports index   function req  res         code      controllers posts js   exports index   function req  res         code     exports show   function req  res         code      However  this setup has a big issue  I have a database- and an app-instance I need to pass to the actions  controllers   js   The only option I could think of  is making both variables global which isn t really a solution  I want to separate routes from the actions because I have a lot of routes and want them in a central place   What s the best way to pass variables to the actions but separate the actions from the routes

User · Accepted Answer

Use req app  req app get  somekey    The application variable created by calling express   is set on the request and response objects   See  https   github com visionmedia express blob 76147c78a15904d4e4e469095a29d1bec9775ab6 lib express js L34-L35

User · Answer

If you want to pass an app-instance to others in Node-Typescript   Option 1  With the help of import  when importing    routes ts import   Application   from  quot express quot   import   categoryRoute   from    routes admin category route  import   courseRoute   from    routes admin course route    const routing    app  Application    gt        app use   api admin category   categoryRoute      app use   api admin course   courseRoute    export   routing    Then import it and pass app  import express    Application   from  express    const app  Application   express    import    routes   then m   gt  m routing app    Option 2  With the help of class    index ts import express    Application   from  express   import   Routes   from    routes     const app  Application   express    const rotues   new Routes app       Here we will access the app in the constructor of Routes Class    routes ts import   Application   from  express  import   categoryRoute   from     routes admin category route  import   courseRoute   from     routes admin course route    class Routes       constructor private app  Application            this apply               private apply    void          this app use   api admin category   categoryRoute         this app use   api admin course   courseRoute           export   Routes

User · Answer

Node js supports circular dependencies Making use of circular dependencies instead of require    routes   app  cleans up a lot of code and makes each module less interdependent on its loading file   app js  var app   module exports   express      now app js can be required to bring app into any file    some app middleware setup  etc  including  app use app router    require    routes      module exports must be defined before this line    routes index js  var app   require     app     app get      function req  res  next      res render  index           require in some other route files   each of which requires app independently require    user    require    blog       -----04 2014 update----- Express 4 0 fixed the usecase for defining routes by adding an express router   method  documentation - http   expressjs com 4x api html router  Example from their new generator  Writing the route  https   github com expressjs generator blob master templates js routes index js Adding namespacing it to the app  https   github com expressjs generator blob master templates js app js L24  There are still usecases for accessing app from other resources  so circular dependencies are still a valid solution

User · Answer

Like I said in the comments  you can use a function as module exports  A function is also an object  so you don t have to change your syntax   app js  var controllers   require    controllers    app  app      controllers js  module exports   function params        return require  controllers index   params       controllers index js  function controllers params      var app   params app     controllers posts   require    posts       controllers index   function req  res           code         module exports   controllers

User · Answer

Or just do that   var app   req app   inside the Middleware you are using for these routes  Like that   router use   req res next    gt        app   req app      next

User · Answer

To make your db object accessible to all controllers without passing it everywhere  make an application-level middleware which attachs the db object to every req object  then you can access it within in every controller       app js let db            your db object initialized const contextMiddleware    req  res  next    gt      req db db    next       app use contextMiddleware      to avoid passing app instance everywhere  instead  passing routes to where the app is      routes js  It s just a mapping  exports routes             controllers index        posts   controllers posts index        posts  post   controllers posts show         app js var   routes        require    routes    routes forEach route   gt  app get    route       You can customize this according to your own needs  like adding post request   The final app js       app js var express     require  express    var app         express createServer     let db            your db object initialized const contextMiddleware    req  res  next    gt      req db db    next       app use contextMiddleware    var   routes        require    routes    routes forEach route   gt  app get    route     app listen 3000  function       console log  Application is listening on port 3000          Another version  you can customize this according to your own needs  like adding post request     routes js  It s just a mapping  let get     path  callback     gt    app    gt     app get path  callback     let post     path  callback     gt    app    gt     app post path  callback     let someFn     path  callback     gt    app    gt           custom logic   app get path  callback     exports routes       get  path       callback  controllers index      post  path    posts   callback  controllers posts index      someFn  path    posts  post   callback  controllers posts show           app js var   routes        require    routes    routes forEach route   gt  route  app

User · Answer

Let s say that you have a folder named  contollers    In your app js you can put this code   console log  Loading controllers        var controllers        var controllers path   process cwd       controllers   fs readdirSync controllers path  forEach function  file        if  file indexOf   js      -1            controllers file split      0     require controllers path         file             console log  Controllers loaded               ok           and      router get   ping   controllers ping pinging     in your controllers forlder you will have the file  ping js  with this code   exports pinging   function req  res  next       console log  ping            And this is it

User · Answer

For database separate out Data Access Service that will do all DB work with simple API and avoid shared state   Separating routes setup looks like overhead  I would prefer to place a configuration based routing instead  And configure routes in  json or with annotations

[node.js] Express: How to pass app-instance to routes from a different file?

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