How to create global variables accessible in all views using Express / Node.JS?
node.jsExpresssails.jsTemplate EngineEjsnode.js Problem Overview
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?
node.js Solutions
Solution 1 - node.js
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: '[email protected]'
}
});
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.
Solution 2 - node.js
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.
Solution 3 - node.js
For Express 4.0 I found that using application level variables works a little differently & 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 & 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
Solution 4 - node.js
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
Solution 5 - node.js
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 <% console.log(site_url); %>
in js files console.log(site_url);
Solution 6 - node.js
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 + '] => app listening on port 3001!');
});
Elaborating with a screenshot from @RamRovi example with slight enhancement.
Solution 7 - node.js
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
<!DOCTYPE html>
<html lang="fr">
<head>
<meta charset="UTF-8">
<title><%= web.title %></title>
<link rel="stylesheet" type="text/css" href="/css/<%= web.cssFile %>">
</head>
</body>
</html>
Hoping it will help
Solution 8 - node.js
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/