Global Variable in app js accessible in routes

Question

How do i set a variable in app js and have it be available in all the routes  atleast in the index js file located in routes  using the express framework and node js

User · Answer

To declare a global variable you need do use global object. Like global.yourVariableName. But it is not a true way. To share variables between modules try to use injection style like

someModule.js:

module.exports = function(injectedVariable) {
    return {
        somePublicMethod: function() {
        },
        anotherPublicMethod: function() {
        },
    };
};

app.js

var someModule = require('./someModule')(someSharedVariable);

Or you may use surrogate object to do that. Like hub.

someModule.js:

var hub = require('hub');

module.somePublicMethod = function() {
    // We can use hub.db here
};

module.anotherPublicMethod = function() {
};

app.js

var hub = require('hub');
hub.db = dbConnection;
var someModule = require('./someModule');

User · Answer

It is actually very easy to do this using the  set  and  get  methods available on an express object   Example as follows  say you have a variable called config with your configuration related stuff that you want to be available in other places   In app js   var config   require    config     app configure function             app set  config   config              In routes index js  exports index   function req  res     var config   req app get  config         config is now available

User · Answer

this is pretty easy thing  but people s answers are confusing and complex at the same time    let me show you how you can set global variable in your express app  So you can access it from any route as needed   Let s say you want set a global variable from your main   route  router get       req  res  next    gt       req app locals somethingNew    Hi setting new global var         So you ll get req app from all the routes  and then you ll have to use the locals to set global data into  like above show you re all set  now I will show you how to use that data  router get   register    req  res  next    gt       console log req app locals somethingNew         Like above from register route you re accessing the data has been set earlier   This is how you can get this thing working

User · Answer

I solved the same problem  but I had to write more code  I created a server js file  that uses express to register routes  It exposes a function register   that can be used by other modules to register their own routes  It also exposes a function  startServer   to start listening to a port  server js  const express   require  express    const app   express     const register    path method callback    gt  methodCalled path  method  callback   const methodCalled    path  method  cb    gt      switch  method        case  get         app get path   req  res    gt  cb req  res         break                        default        console log  there has been an error           const startServer    port    gt  app listen port       gt   console log  successfully started at   port       module exports       register    startServer     In another module  use this file to create a route   help js  const app   require     server     const registerHelp        gt      app register   help   get   req  res    gt        res send  This is the help section           app register   help   post   req  res    gt        res send  This is the help section          module exports       registerHelp     In the main file  bootstrap both   app js  require    server   startServer 7000  require    web help   registerHelp

User · Answer

the easiest way is to declare a global variable in your app js  early on   global mySpecialVariable    something    then in any routes you can get it   console log mySpecialVariable

User · Answer

My preferred way is to use circular dependencies   which node supports   in app js define var app   module exports   express    as your first order of business Now any module required after the fact can var app   require    app   to access it   app js  var express     require  express    var app   module exports   express      now app js can be required to bring app into any file    some app middleware  config  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

User · Answer

As others have already shared  app set  config   config  is great for this  I just wanted to add something that I didn t see in existing answers that is quite important  A Node js instance is shared across all requests  so while it may be very practical to share some config or router object globally  storing runtime data globally will be available across requests and users  Consider this very simple example   var express   require  express    var app   express     app get   foo   function req  res        app set  message    Welcome to foo         res send app get  message          app get   bar   function req  res        app set  message    Welcome to bar             some long running async function     var foo   function             res send app get  message                setTimeout foo  1000        app listen 3000     If you visit  bar and another request hits  foo  your message will be  Welcome to foo    This is a silly example  but it gets the point across   There are some interesting points about this at Why do different node js sessions share variables

User · Answer

To make a global variable  just declare it without the var keyword   Generally speaking this isn t best practice  but in some cases it can be useful - just be careful as it will make the variable available everywhere    Here s an example from visionmedia screenshot-app  file app js          Module dependencies       var express   require  express       stylus   require  stylus       redis   require  redis       http   require  http     app   express           require   route files   file routes main js    we can now access  app  without redeclaring it or passing it in           GET home page       app get      function req  res  next     res render  index

User · Answer

I used app all     The app all   method is useful for mapping    global    logic for specific   path prefixes or arbitrary matches    In my case  I m using confit for configuration management   app all      function  req  res  next        confit basedir  create function  err  config            if  err                throw new Error  Failed to load configuration    err                     app set  config   config           next                  In routes  you simply do req app get  config   get  cookie

User · Answer

A neat way to do this is to use app locals provided by Express itself  Here is the documentation      In app js  app locals variable you need   42      In index js exports route   function req  res       var variable i needed   req app locals variable you need

User · Answer

Here are explain well  in short   http   www hacksparrow com global-variables-in-node-js html  So you are working with a set of Node modules  maybe a framework like Express js  and suddenly feel the need to make some variables global  How do you make variables global in Node js   The most common advice to this one is to either  declare the variable without the var keyword  or  add the variable to the global object  or  add the variable to the GLOBAL object   Which one do you use   First off  let s analyze the global object  Open a terminal  start a Node REPL  prompt     gt  global name undefined  gt  global name    El Capitan   gt  global name  El Capitan   gt  GLOBAL name  El Capitan   gt  delete global name true  gt  GLOBAL name undefined  gt  name    El Capitan   El Capitan   gt  global name  El Capitan   gt  GLOBAL name  El Capitan   gt  var name    Sparrow  undefined  gt  global name  Sparrow

User · Answer

This was a helpful question  but could be more so by giving actual code examples   Even the linked article does not actually show an implementation   I  therefore  humbly submit   In your app js file  the top of the file   var express   require  express     http   require  http     path   require  path     app   express      IMPORTANT   define the global app variable prior to requiring routes   var routes   require    routes      app js will not have any reference to app get   method   Leave these to be defined in the individual routes files   routes index js   require    main    require    users      and finally  an actual routes file  routes main js   function index  request  response        response render  index     title   Express         app get     index       lt -- define the routes here now  thanks to the global app variable

User · Answer

John Gordon s answer was the first of dozens of half-explained   documented answers I tried  from many  many sites  that actually worked   Thank You Mr Gordon   Sorry I don t have the points to up-tick your answer   I would like to add  for other newbies to node-route-file-splitting  that the use of the anonymous function for  index  is what one will more often see  so using John s example for the main js  the functionally-equivalent code one would normally find is   app get      req  res        res render  index     title   Express

[node.js] Global Variable in app.js accessible in routes?

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