creating a global object in nodejs accessible by .js modules - javascript

My nodejs project requires memory tables accessible by different .js module. Some modules will update the tables but the data must be the same across all modules(sort of a in memory db). As such, I need a truly global object....not a global per module object. Creating a common.js file with all the objects then require it in all the modules will not do since the data will be global/local to the respective modules. I have seen reference to nodejs globals where global.myobject would be global to all modules but the documentation is not clear as to whether this is so or not. The last discussion I saw was from 2014. Can anyone update me on what is the current situation? How is this problem solved?

In node.js..
if you had a module called common.js, that looked like this..
'use strict';
var obj = {};
module.exports = obj;
And then inside another module you did this
'use strict';
var c = require('./common');
c.test = 1234;
Then later another module did this..
'use strict';
var c = require('./common');
console.log(c);
//output = { test: 1234 }
A module in modejs, is just another object. nodejs, caches any requires, and so will always return the same object.
One gotcha for windows users, windows filenames are not case-sensitive, so if you did require('Common'), and then did require('common'); you would have 2 version of the same module. And this is a good reason to keep all modules names in lowercase.

Related

Are JavaScript classes acceptable Node modules?

Bear with me as I lead you through the process that elicited my question.
I'm working on a CLI app in node and I'm using objects to encapsulate my business logic using this pattern:
// my-project/lib/widget/myobject.js
var MyObject = function(x) {
this.x = x;
};
MyObject.prototype.getX = function() {
return this.x;
};
module.exports = MyObject;
I'm also testing these objects:
// my-project/test/lib/widget/myobject.spec.js
var MyObject = require('../../../lib/widget/myobject.js');
describe('MyObject', function() {
...
});
At one point I was unhappy with the naming and directory structure I had chosen. I found myself tediously counting those parent directory references (..) in several spec files when rewriting the relative paths. I figured there must be an easier way to reference a root directory containing these object definitions.
One of the recommendations I found here suggested "putting application-specific modules into node_modules".
Now, as I understand modules, they are the packages I download from npm and use in my project. They contain libraries of useful things with a single API exported to me when I call require. This is not how I view the simple single-purpose classes built specifically for the internal use of my application.
If you've stuck with me this far, thank you! Here is my question:
How do I make the internals of my application more "modular" so it properly follows the intent of the Node module system while remaining object oriented?
I'm not sure how suitable this is for production or for modules you plan on distributing but in your main file you could add this:
process.env.NODE_PATH = __dirname;
require('module').Module._initPaths();
which would let you always require modules relative to the folder containing your main file. I.e. if you had a file in:
library/some_file.js
then in tests/some_other_file.js you could just do:
require('library/some_file');
Or as an alternative you could add this in your main file:
global.__base = __dirname + '/';
and then in your other modules require using:
var MyObject = require(__base + 'my-project/lib/widget/myobject');

Sharing global variables between javascript files loaded to Meteor

I have a javascript file that I place in the client/lib folder within my Meteor app. As the file grew bigger, I decided to split it into 3 files and define an object 'App' in the global namespace in order for the 3 files to share the data.
Each file starts with
var app = app || {};
(function () {
'use strict';
app.object1 = {
This way, file2 and file3 can still use app.object1, and so on.
The problem is when Meteor loads the files, it seems to automatically wraps it with function(){}, and this makes app.object1 not accessible from files loaded subsequently.
(function(){
var app = app || {};
(function () {
'use strict';
app.object1 = {
What is the best way to avoid this issue? Thanks.
EDIT: I referred to this posting [Link:][1]Global variables in Meteor which suggests defining the variable without "var". I replaced the code in file1 to app = {}, but my app is now crashing in file2 in the following line of code, with the message from the Meteor console pasted below.
app.ALL_LIST = 'all'
=> Your application is crashing. Waiting for file change.
ReferenceError: app is not defined
omit var in your variable declaration ;) then it will be scoped globally.

node.js configure submodules

[EDIT]
Thanks to Stafano that formalized my question in a better way:
You have a module
-) There are several files in this module
-) All these files depend on a configuration whose path is unknown to the module itself
-) This module does not do much on its own, and is meant to be used by other applications
-) These applications should inject a configuration path into the module before it can be used
So i have this module, used from another application. It's composed of other submodules and i want to configure it using a configuration object.
I already tried to inject the configuration in my submodels but i had the same problem exposed in the original question.
For example my module use mongoDB (with mongoose) as a store.
// app.js
// in the config object i have the URI to the mongo instance (in order to create a connection).
var myModule = require('myModule')(config);
// myModule.js
// files
// myModule/index.js expose the module's functionalities
// is the entry point so I create the mongoose connection
var mongoose = require('mongoose');
module.exports = function(config){
var connection = mongoose.createConnection(config.store.URL);
// I need to expose this connection to the others submodules.
}
// myModule/storeController.js contains the business logic that use the store (createItem, deleteItem, get...) and requrie mongoose and my Models (store in the models folder)
var mongoose = require('mongoose');
var Item = require('./models/item.js');
exports.createItem = function(item){
Item.save(item, function(err, item){
if (err) throw
...
});
}
// myModule/models/item.js
// In this module i need to use the connection application in the configuration.
var mongoose = require('mongoose');
var connection = // i don't know how to get it
var ItemSchema = new mongoose.Schema({
name: String
});
module.exports = mongoose.model('item', ItemSchema);
If I inject the configuration obj to the item.js i can't do the module.exports of my model.
I hope that this example can clarify my question, but the problem is the simple, expose an object after get it as a parameter.
[PREVIOUS]
I have a node.js application that require a module. This module accept the coniguration file path (a JSON file).
I need to load that configuration on require and expose it to the module.
How can I achieve this behavior?
Something like:
// app.js
var myModule = require('myModule')(__dirname + '/config/myModuleCnfig.json');
// myModule.js
module.exports = function(configPath){
var config = require(configPath);
module.exports = config; // This is wrong
}
Is there another way to get the configuration path, configure the module and share the configuration??
With "share the configuration" i mean that i want to give the possibility to other files of my module to use that configuration.
Thanks for any suggestions!
FINAL EDIT:
After many misunderstandings, your problem is finally clear to me. To summarise what's in the comments, here is the situation:
You have a module
There are several files in this module
All these files depend on a configuration whose path is unknown to the module
itself
This module does not do much on its own, and is meant to be
used by other applications
These applications should inject a
configuration path into the module before it can be used
Since you cannot modify dynamically what a module exports, you should use another approach. As with most situations that you encounter in programming, there is not one way which is always right, as much pedends on your requirements and limitations.
The easiest way to do this (which I don't recommend) is to use a global variable, which you set in your myModule.js file and will be used by the other files in your module. The biggest drawback of this approach is that you wouldn't be able to use multiple instances of the module at the same time with different configurations. Also, any other module could easily modify (deliberately or not) you configuration at any time, by simply changing the value of the global variable, so it's also a security risk.
A much better way, which will probably require more work on your part - depending on how many files you have - is to implement some kind of Inversion of Control (IoC). In your case, you could turn all your exports into functions that accept a config, and then initialise them by passing the active configuration after you require the module. I don't know the specifics of your implementation, so here is some sample code:
// submodule1.js
module.exports = function(config) {
// return something that uses the configuration
}
// myModule.js
var fs = require('fs');
var submodule1 = require('./submodule1');
var submodule2 = require('./submodule2');
// ...
module.exports = function(configPath){
var config = JSON.parse(fs.readFileSync(configPath));
var sm1 = submodule1(config);
var sm2 = submodule2(config);
return /* an object that uses sm1 and sm2 */;
}
If your module is quite complex, you can use some IoC library that does the binding for you. An good one could be Electrolite.
Hope this helps.
PREVIOUS ANSWER:
You can use a library called jsop:
var jsop = require('jsop');
var config = jsop('./config/myModuleCnfig.json');
If you don't want to add a dependency to this module, the linked GitHub page also has a snippet that you can use to load the json config using only native methods.
EDIT: I just realised that this module is only for node 0.11, which you are probably not using. Since you don't probably need the writing functionality, you can use the following snippet instead:
var fs = require('fs')
var config = JSON.parse(fs.readFileSync('./config/myModuleCnfig.json'))
EDIT 2:
Now I think I understand your problem better. To pass the path to the required configuration, you can do something like this:
// myModule.js
var fs = require('fs')
module.exports = function(configPath){
var config = JSON.parse(fs.readFileSync(configPath))
return config;
}

In Node.js, how can I load my modules once and then use them throughout the app?

I want to create one global module file, and then have all my files require that global module file. Inside that file, I would load all the modules once and export a dictionary of loaded modules.
How can I do that?
I actually tried creating this file...and every time I require('global_modules'), all the modules kept reloading. It's O(n).
I want the file to be something like this (but it doesn't work):
//global_modules.js - only load these one time
var modules = {
account_controller: '/account/controller.js',
account_middleware: '/account/middleware.js',
products_controller: '/products/controller.js',
...
}
exports.modules = modules;
1. Using a magic variable (declared without var)
Use magic global variables, without var.
Example:
fs = require("fs");
instead of
var fs = require("fs");
If you don't put var when declaring the variable, the variable will be a magic global one.
I do not recommend this. Especially, if you are in the strict mode ("use strict") that's not going to work at all.
2. Using global.yourVariable = ...
Fields attached to global object become global variables that can be accessed from anywhere in your application.
So, you can do:
global.fs = require("fs");
This is not that bad like 1., but still avoid it when possible.
For your example:
Let's say you have two files: server.js (the main file) and the global_modules.js file.
In server.js you will do this:
require("./global_modules");
and in global_modules.js you will have:
_modules = {
account_controller: require('/account/controller.js'),
account_middleware: require('/account/middleware.js'),
products_controller: require('/products/controller.js'),
...
}
or
global._modules = {...}
In server.js you will be able to do:
_modules.account_controller // returns require('/account/controller.js'),
require already does it. Try loading a module, modify it and then load it another time in another place or file:
var fs = require('fs'):
console.log(fs.hey);
fs.hey = 'HEY TIMEX, WHATS UP?';
//another place of the same process
var fs = require('fs');
console.log(fs.hey);

How to reuse commonjs modules in the browser and server using modulr?

I'm using modulr for using commonjs modules in the browser.
The goal is to be able to reuse some of those modules also in a server environment.
These "shared" modules need to do something like this:
var _ = _ || require("underscore");
meaning:
if _ exists as a global var (browser environment), use it
else load the "underscore" module (server), and use it instead
Now, since modulr does static analysis in all the code, looking for the require calls in order to generate the final js file, it will fail the build.
Is there a way to work around this problem?
(For example, if modulr supported something like --ignore=<module_list> parameter, everything would run fine.)
Apparently there's no way to fix this in modulr, so I had to create a workaround module named Env which looks like this:
// Env.js
var my = {
modules: undefined,
require: require
};
exports.override = function(modules) {
my.modules = modules;
};
exports.require = function(path) {
if (my.modules && my.modules[path]) {
return my.modules[path];
} else {
// my.require(...) is needed instead of simply require(...)
// because simply require(...) will cause a modulr parsing failure
return my.require(path);
}
};
And at the client side, have a specific initializer that does:
// ClientInitializer.js
Env = require('shared/Env');
Env.override({ underscore: _ });
So, the "shared" modules can do:
// SharedModule.js
var _ = require('shared/Env').require('underscore');
If the "shared" module is running in the server, the normal require function is called.
If it is running in the browser, the Env module will answer with the global _ variable.

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