How to create global variables accessible in all views using Express Node JS

Question

Ok  so I have built a blog using Jekyll and you can define variables in a file  config yml which are accessible in all of the templates layouts  I am currently using Node JS   Express with EJS templates and ejs-locals  for partials layouts  I am looking to do something similar to the global variables like site title that are found in  config yml if anyone is familiar with Jekyll   I have variables like the site s title   rather than page title   author company name  which stay the same on all of my pages    Here is an example of what I am currently doing    exports index   function req  res       res render  index              siteTitle   My Website Title           pageTitle   The Root Splash Page           author   Cory Gross           description   My app description           indexSpecificData  someData             exports home   function  req  res        res render  home             siteTitle   My Website Title           pageTitle   The Home Page           author   Cory Gross           description   My app description           homeSpecificData  someOtherData              I would like to be able to define variables like my site s title  description  author  etc in one place and have them accessible in my layouts templates through EJS without having to pass them as options to each call to res render  Is there a way to do this and still allow me to pass in other variables specific to each page

User · Answer

For Express 4 0 I found that using application level variables works a little differently  amp  Cory s answer did not work for me   From the docs  http   expressjs com en api html app locals  I found that you could declare a global variable for the app in   app locals   e g  app locals baseUrl    http   www google com    And then in your application you can access these variables  amp  in your express middleware you can access them in the req object as  req app locals baseUrl   e g   console log req app locals baseUrl    prints out http   www google com

User · Answer

You can do this by adding them to the locals object in a general middleware   app use function  req  res  next       res locals          siteTitle   My Website s Title        pageTitle   The Home Page        author   Cory Gross        description   My app s description            next          Locals is also a function which will extend the locals object rather than overwriting it  So the following works as well  res locals     siteTitle   My Website s Title     pageTitle   The Home Page     author   Cory Gross     description   My app s description         Full example  var app   express     var middleware          render  function  view            return function  req  res  next                res render view                         globalLocals  function  req  res  next            res locals                siteTitle   My Website s Title               pageTitle   The Root Splash Page               author   Cory Gross               description   My app s description                       next                index  function  req  res  next            res locals               indexSpecificData  someData                     next                app use middleware globalLocals   app get      middleware index  middleware render  home     app get   products   middleware products  middleware render  products       I also added a generic render middleware  This way you don t have to add res render to each route which means you have better code reuse  Once you go down the reusable middleware route you ll notice you will have lots of building blocks which will speed up development tremendously

User · Answer

What I do in order to avoid having a polluted global scope is to create a script that I can include anywhere      my-script js const ActionsOverTime   require   bigteam node-aot   ActionsOverTime  const config   require        config config   actionsOverTime  let aotInstance    function        if   aotInstance        console log  Create new aot instance        aotInstance   ActionsOverTime createActionOverTimeEmitter config              exports   aotInstance    Doing this will only create a new instance once and share that everywhere where the file is included  I am not sure if it is because the variable is cached or of it because of an internal reference mechanism for the application  that might include caching   Any comments on how node resolves this would be great   Maybe also read this to get the gist on how require works  http   fredkschott com post 2014 06 require-and-the-module-system

User · Answer

In your app js you need add something like this  global myvar   100    Now  in all your files you want use this variable  you can just access it as myvar

User · Answer

After having a chance to study the Express 3 API Reference a bit more I discovered what I was looking for  Specifically the entries for app locals and then a bit farther down res locals held the answers I needed   I discovered for myself that the function app locals takes an object and stores all of its properties as global variables scoped to the application  These globals are passed as local variables to each view  The function res locals  however  is scoped to the request and thus  response local variables are accessible only to the view s  rendered during that particular request response   So for my case in my app js what I did was add   app locals       site            title   ExpressBootstrapEJS           description   A boilerplate for a simple web application with a Node JS and Express backend  with an EJS template with using Twitter Bootstrap              author            name   Cory Gross           contact   CoryG89 gmail com              Then all of these variables are accessible in my views as site title  site description  author name  author contact   I could also define local variables for each response to a request with res locals  or simply pass variables like the page s title in as the optionsparameter in the render call   EDIT  This method will not allow you to use these locals in your middleware  I actually did run into this as Pickels suggests in the comment below  In this case you will need to create a middleware function as such in his alternative  and appreciated  answer  Your middleware function will need to add them to res locals for each response and then call next  This middleware function will need to be placed above any other middleware which needs to use these locals   EDIT  Another difference between declaring locals via app locals and res locals is that with app locals the variables are set a single time and persist throughout the life of the application  When you set locals with res locals in your middleware  these are set everytime you get a request  You should basically prefer setting globals via app locals unless the value depends on the request req variable passed into the middleware  If the value doesn t change then it will be more efficient for it to be set just once in app locals

User · Answer

With the differents answers  I implemented this code to use an external file JSON loaded in  app locals   Parameters         web              title     Le titre de ma Page            cssFile     20200608 1018 css            Application  var express       require  express    var appli         express    var serveur       require  http   Server appli    var myParams      require    include my params json    var myFonctions   require    include my fonctions js     appli locals   myParams    EJS Page   lt  DOCTYPE html gt   lt html lang  fr  gt   lt head gt       lt meta charset  UTF-8  gt       lt title gt  lt    web title   gt  lt  title gt       lt link rel  stylesheet  type  text css  href   css  lt    web cssFile   gt   gt   lt  head gt    lt  body gt   lt  html gt    Hoping it will help

User · Answer

One way to do this by updating the app locals variable for that app in app js  Set via following  var app   express    app locals appName    DRC on FHIR     Get   Access  app listen 3000  function          console log       app locals appName        gt  app listening on port 3001           Elaborating with a screenshot from  RamRovi example with slight enhancement

User · Answer

you can also use  global    Example   declare like this      app use function req res next         global site url   req headers host       hostname    localhost 8080        next             Use like this    in any views or ejs file       lt             console log site url              in js files      console log site url

[node.js] How to create global variables accessible in all views using Express / Node.JS?

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