In Node.js, when you do
var otherscript = require('otherscript');
it runs the script upon the require
I am wondering if there is a way to "require" a script without running it, so that you can run it later when you want to.
Is there any good reason why not?
If you can edit the 'otherscript' (no one else is using that script) then you can simply enclose the whole code inside a function and add it to exports.
Example:
otherscript:
module.exports = function(){
//original code goes here
};
Then use as:
var otherscript = require('otherscript');
var obj = otherscript();
When you require a file or module, the return of that file/module is cached. In other words, it is really only executed once, and subsequent calls to require() of that file/module will only return a reference to the exact same object.
A common example of this is the Mongoose package, where calling require('mongoose') will return an instance of mongoose, on which you can call connect() to connect to the database. Calling require('mongoose') again in a different part of your program will return the same instance with the same database connection made available.
Related
I am writing tests for a service that uses knex, however, since the knex calls has several uses of knex.fn.now() my tests will produce varied results over time. I'm wondering if it's possible to mock/spy/hijack the inner calls to knex.fn.now() to something I can control, while letting the rest of the code stay in its 'real' implementation. I can only find examples of mocking knex completely which would make the purpose of my testing pointless.
So I'm wondering if it's possible to have jest listen for a specific function call and insert another value in it's stead.
You can mock Knex package by creating a folder __mocks__/knex/index.js.
Inside this file u can require the real knex implementation, change it, and export.
It should look something like this:
// __mocks__/knex/index.js
const knex = require('knex');
const fixedTime = new Date();
knex.fn.now = () => fixedTime;
module.exports = knex;
I am developing Chatbot using Azure functions. I want to load the some of the conversations for Chatbot from a file. I am looking for a way to load these conversation data before the function app starts with some function callback. Is there a way load the conversation data only once when the function app is started?
This question is actually a duplicate of Azure Function run code on startup. But this question is asked for C# and I wanted a way to do the same thing in NodeJS
After like a week of messing around I got a working solution.
First some context:
The question at hand, running custom code # App Start for Node JS Azure Functions.
The issue is currently being discussed here and has been open for almost 5 years, and doesn't seem to be going anywhere.
As of now there is an Azure Functions "warmup" trigger feature, found here AZ Funcs Warm Up Trigger. However this trigger only runs on-scale. So the first, initial instance of your App won't run the "warmup" code.
Solution:
I created a start.js file and put the following code in there
const ErrorHandler = require('./Classes/ErrorHandler');
const Validator = require('./Classes/Validator');
const delay = require('delay');
let flag = false;
module.exports = async () =>
{
console.log('Initializing Globals')
global.ErrorHandler = ErrorHandler;
global.Validator = Validator;
//this is just to test if it will work with async funcs
const wait = await delay(5000)
//add additional logic...
//await db.connect(); etc // initialize a db connection
console.log('Done Waiting')
}
To run this code I just have to do
require('../start')();
in any of my functions. Just one function is fine. Since all of the function dependencies are loaded when you deploy your code, as long as this line is in one of the functions, start.js will run and initialize all of your global/singleton variables or whatever else you want it to do on func start. I made a literal function called "startWarmUp" and it is just a timer triggered function that runs once a day.
My use case is that almost every function relies on ErrorHandler and Validator class. And though generally making something a global variable is bad practice, in this case I didn't see any harm in making these 2 classes global so they're available in all of the functions.
Side Note: when developing locally you will have to include that function in your func start --functions <function requiring start.js> <other funcs> in order to have that startup code actually run.
Additionally there is a feature request for this functionality that can voted on open here: Azure Feedback
I have a similar use case that I am also stuck on.
Based on this resource I have found a good way to approach the structure of my code. It is simple enough: you just need to run your initialization code before you declare your module.exports.
https://github.com/rcarmo/azure-functions-bot/blob/master/bot/index.js
I also read this thread, but it does not look like there is a recommended solution.
https://github.com/Azure/azure-functions-host/issues/586
However, in my case I have an additional complication in that I need to use promises as I am waiting on external services to come back. These promises run within bot.initialise(). Initialise() only seems to run when the first call to the bot occurs. Which would be fine, but as it is running a promise, my code doesn't block - which means that when it calls 'listener(req, context.res)' it doesn't yet exist.
The next thing I will try is to restructure my code so that bot.initialise returns a promise, but the code would be much simpler if there was a initialisation webhook that guaranteed that the code within it was executed at startup before everything else.
Has anyone found a good workaround?
My code looks something like this:
var listener = null;
if (process.env.FUNCTIONS_EXTENSION_VERSION) {
// If we are inside Azure Functions, export the standard handler.
listener = bot.initialise(true);
module.exports = function (context, req) {
context.log("Passing body", req.body);
listener(req, context.res);
}
} else {
// Local server for testing
listener = bot.initialise(false);
}
You can use global variable to load data before function execution.
var data = [1, 2, 3];
module.exports = function (context, req) {
context.log(data[0]);
context.done();
};
data variable initialized only once and will be used within function calls.
I'm building a project with AdonisJS, and I want to build it as a modular, two-part application: The AdonisJS server runs a control panel, and a custom script outside that server runs an IRC bot. I've been trying to load Lucid into the second script so that I can interface with my database, but it only ever returns an empty object, {}. Some things to note:
I've made sure my database is populated.
I've tested code in my controllers that works and fetches results as expected.
The secondary script boots up all the same parts of Adonis as server.js, sans the actual HTTP server.
I have tried attaching this script to an HTTP server but it made no difference.
I have also tried creating raw QueryBuilder objects with the same results.
Here's the least amount of code I can put together as an example:
#!/usr/bin/node
'use strict'
const fs = require('fs')
const bootstrap = require('./bootstrap/bot')
bootstrap(() =>
{
const AppConfig = use('AppConfig')
const Settings = use('App/Model/Settings')
const get_settings = function * () {
yield Settings.all()
}
console.log(get_settings())
})
console.log() prints {}, even though the same code called within a controller prints all entries from the settings table. bootstrap/bot.js is almost an exact replica of bootstrap/http.js. The only difference is that it doesn't start an HTTP server.
I've scoured the source code looking for things that might happen between starting the server and running controller code to see if there's something critical I'm missing, but I'm lost.
Does anyone know how I can use my Lucid models outside the confines of AdonisJS controllers?
It's because your function is a generator and you can only call a generator with the yield keyword.
So your console.log() should looks like console.log(yield get_settings()).
You may use the package co to create the root generator function.
bootstrap(co(function * () {
// ...
}))
I have a module for connecting to my DB and perform actions.
Then in my main script (app.js) I instantiate it like
var DBConn = require('./common/DBConn');
And from that script it works fine. But then I've got some other scripts that handle routes, and I want to perform some DB stuff on those, but if I use DBConn it returns an error saying "DBConn is not defined".
Then I can just instantiate another DBConn in these other js files, but this would mean I am creating a connection for each file, right? But I want these other scripts to use the DBConn object from the app.js, so that I'm not constantly establishing a connection to the DB and then closing it... (unless this is a good idea, but to me it makes more sense to have just one "global" object dealing with the connection over all the app and that's it).
(BTW: I'm using Express)
You want to require() your module in each file. Node will cache the module.
Typically, the context of a DB connection is abstracted away behind stores or repositories and your other modules interact with those. In cases where people are directly requiring modules like mongoose, they'll require mongoose everywhere but only call the connection code within their main application entry point (app.js/server.js/whatever).
https://nodejs.org/api/modules.html#modules_caching
Modules are cached after the first time they are loaded. This
means (among other things) that every call to require('foo') will get
exactly the same object returned, if it would resolve to the same
file.
Multiple calls to require('foo') may not cause the module code to be
executed multiple times. This is an important feature. With it,
"partially done" objects can be returned, thus allowing transitive
dependencies to be loaded even when they would cause cycles.
If you want to have a module execute code multiple times, then export
a function, and call that function.
You could use a singleton to solve this issue for you. Please remember however that singletons come with their own set of problems (a good discussuon on singletons can be found here What is so bad about singletons?).
That said once you take into consideration the pro's and cons of singletons they can be a fantastic solution to exactly this problem.
Example:
// database.js
var singleton = function singleton() {
this.DbConnection = {};
function setup(database, username, password) {
this.DbConnection = MakeDbConnection()
};
};
singleton.instance = null;
singleton.getInstance = function(){
if(this.instance === null){
this.instance = new singleton();
}
return this.instance;
};
module.exports = singleton.getInstance();
This can then be called elsewhere in your application like so...
// main.js
var db = require("./database");
db.setup('db', 'root', 'pass');
db.DbConnection();
Once you have called db.setup() the first time, the db connection will be available just with the following:
// elsewhere.js
var db = require("./database");
db.DbConnection();
I am new to the 'nodejs' world.So wanting to explore the various technologies,frameworks involved i am building a simple user posts system(users posting something everybody else seeing the posts) backed by redis.I am using express framework which is recommended by most tutorials.But i have some difficulty in gettting data from the redis server i need to do 3 queries from the redis server to display the posts.In which case have to use neested callback after each redis call.So i wanted to use streamline.js to simplify the callbacks.But i am unable to get it to work even after i used npm install streamline -g and require('streamline').register(); before calling
var keys=['comments','timestamp','id'];
var posts=[];
for(var key in keys){
var post=client.sort("posts",'by','nosort',"get","POST:*->"+keys[key],_);
posts.push(post);
}
i get the error ReferenceError: _ is not defined.
Please point me in the right direction or point to any resources i might have missed.
The require('streamline').register() call should be in the file that starts your application (with a .js extension). The streamline code should be in another file with a ._js extension, which is required by the main script.
Streamline only allows you to have async calls (calls with _ argument) at the top level in a main script. Here, your streamline code is in a module required by the main script. So you need to put it inside a function. Something like:
exports.myFunction = function(_) {
var keys=['comments','timestamp','id'];
var posts=[];
for(var key in keys){
var post=client.sort("posts",'by','nosort',"get","POST:*->"+keys[key],_);
posts.push(post);
}
}
This is because require is synchronous. So you cannot put asynchronous code at the top level of a script which is required by another script.