Develop Reference

Singleton ES6 Module being called multiple times?

I am not sure why the module here which has a console.log is being called multiple times. I thought this was a singleton.
So if I'm importing this module into other modules, since this is a singleton I did not expect the console.log to be called every time...only the first time it's imported by a module but after that I thought that, even when imported by subsequent modules, since it's a singleton, then I shouldn't see a ton of these being logged:
src/graphql/db/InMemory/InMemoryDB.ts
console.log('inMemoryDB');
const inMemoryDb = newDb();
inMemoryDb.public.none(fs.readFileSync('001-initial.sql', 'utf8'));
export default inMemoryDb;
what I'm seeing when I run initially run tests or initially start my service which uses this singleton, are 6-7 inMemoryDB being logged. Even after I changed it to this, same deal:
const inMemoryDb = () => {
console.log('inMemoryDB');
return newDb();
}
inMemoryDb.public.none(fs.readFileSync('001-initial.sql', 'utf8'));
export default inMemoryDb();
So for example when I start my graphql service, I get like 6-7 of those console.logs when I run yarn graphql-dev
"graphql-dev": "yarn compile-graphql && yarn start-graphql-dev",
"compile-graphql": "tsc -b ./src/graphql",
"start-graphql-dev": "node --optimize_for_size --trace-warnings --es-module-specifier-resolution=node --no-warnings dist/graphql/server.js"
deep down in my graphql code, it uses that in-memory DB singleton like this (based on the first implementation above):
const inMemoryPgDb = inMemoryDb;

Agree with you that the call happens and console.log is called but the value of variable does not change.
Check the example for reference
Singleton example
OK, Why there is multiple console.log ?
In the above code you are giving a function instance with return type and wherever the module function is referred it gets called. since we are executing that function.
Each module is separate JavaScript program. It combines into a single program
at the time of execution.

How to get Jest to see the functions I am writing for MongoDB Stitch?

I am trying out Stitch, a serverless/hosted JavaScript environment from MongoDB. My main purpose is to help me learn modern JavaScript, but I am trying to write a useful app as well.
I have written the following function, and saved it in my Stitch app. I believe this follows the documented way to write functions in Stitch, and I have tested it from the Stitch administration console:
exports = function(query){
const http = context.services.get("HTTP");
const urlBase = context.values.get("stackOverflowApiUrl");
const options = [
'order=desc',
'sort=activity',
'site=stackoverflow',
'q=' + encodeURIComponent(query),
'user=472495',
'filter=!--uPQ.wqQ0zW'
];
return http
.get({ url: urlBase + '?' + options.join('&') })
.then(response => {
// The response body is encoded as raw BSON.Binary. Parse it to JSON.
const ejson_body = EJSON.parse(response.body.text());
return ejson_body.total;
});
};
This code is pretty simple - it obtains an http object for making external API fetches, and obtains a configuration value for a URL urlBase to contact (resolving to https://api.stackexchange.com/2.2/search/excerpts) and then makes a call to the Stack Overflow Data API. This runs a search query against my user and returns the number of results.
So far so good. Now, I want to call this function locally, in Jest. To do this, I have installed Node and Jest in a local Docker container, and have written the following test function:
const callApi = require('./source');
test('Simple fetch with no user', () => {
expect(callApi('hello')).toBe(123);
});
This fails, with the following error:
~ # jest
FAIL functions/callApi/source.test.js
✕ Simple fetch with no user (3ms)
● Simple fetch with no user
TypeError: callApi is not a function
2 |
3 | test('Simple fetch with no user', () => {
> 4 | expect(callApi('hello')).toBe(123);
| ^
5 | });
6 |
at Object.<anonymous>.test (functions/callApi/source.test.js:4:12)
Test Suites: 1 failed, 1 total
Tests: 1 failed, 1 total
Snapshots: 0 total
Time: 1.418s
Ran all test suites.
(In fact I was expecting it to fail, since it contains a global object context that Jest does not have access to. I will work out how to mock that later, but for now Jest cannot even see the function at all).
I suspect I can see the reason - in the Jest introduction docs, one has to do this for the SUT:
module.exports = function() { ... }
However the Stitch docs seem to require functions to be defined as:
exports = function() { ... }
I do not have a background in JavaScript to understand the difference. I could try module.exports in Stitch, but I would rather not, since this would either not work now, or cause a breakage in the future. Can Jest be instructed to "see" bare exports without the module prefix?
Incidentally, I have picked Jest because it is popular, and because some of my JavaScript colleagues vouch for it. However, I am not wedded to it, and would be happy to use something else if it is known to be better for Stitch development.
Update
Following the useful answer from jperl below, I find that the following construction is not possible in Stitch:
module.exports = exports = function() {}
I also cannot do this:
exports = function() {}
module.exports = exports
If I try either, I get the following error:
runtime error during function validation
So it looks like I have to get Jest to work without module.exports, or create a glue file that imports the exports version into module.exports, with the main file being used by Stitch, and the glue importer being used by Jest.

I suggest you to read this thread. And you're right in thinking it has to do with modules.exports vs exports. The thing is that module.exports and exports first point to the same thing. So something like this works:
//modify the same object that modules.exports is pointing to
exports.a = {}
exports.b = {}
but this won't:
exports = {}
Why? Because now exports points to something else than module.exports so what you're doing has no effect at all.
Update
Following some updates in the comments, we came to the view that Stitch does not seem to support the export format that Jest requires.

This is an addendum to jperl's answer, to show how I got Jest working while respecting Stitch's limitations.
Firstly, it is worth noting how a Stitch application is laid out. This is determined by the import/export format.
auth_providers/
functions/
function_name_1/
config.json
source.js
function_name_2/
config.json
source.js
...
services/
values/
The config.json file is created by Stitch remotely, and is obtained through a export. This contains ID information to uniquely identify the function in the same folder.
I believe it is common JavaScript practice to mix tests with source code, so I am following that style (I am new to modern JS, and I confess I find this style untidy, but I am running with it nevertheless). Thus I add a source.test.js file in each function folder.
Finally, since there is a discrepancy between what Stitch requires and what Jest requires, I have written a script to create a source code file under _source.js in each function folder.
So, each folder will contain these files (the underscore files will probably be ignored by Git, as they will always be generated):
_source.js
config.json
source.js
source.test.js
In order to create the underscored copies, I am using this shell script:
#!/bin/bash
# Copy all source.js files as _source.js
for f in $(find functions/ -name source.js); do cp -- "$f" "$(dirname $f)/_$(basename $f)"; done
# Search and replace in all _source.js files
for f in $(find functions/ -name _source.js); do sed -i -e 's/exports =/module.exports =/g' $f; done
A bit hacky perhaps, but it works!

Cypress custom command is not recognized when invoked

I've created the following custom command in my cypress/support/commands.js file.
Cypress.Commands.add("login", (username, password) => {
cy.request({
method: 'POST',
form: true,
url: '/test/login/',
body: {'username': username, 'password': password}
})
})
I had tests passing and login working before moving the login functionality to this custom command. I'm invoking it in my spec with cy.login(testuser, testpwd), but I'm getting the following error message: TypeError: cy.login is not a function. The docs say that /cypress/support/commands.js is loaded before any test files are evaluated, so I assumed that simply placing a custom command in there would make the command available. I'm running the tests through the local (GUI) test runner.

All the code and referenced modules in index.js are loaded before your test file. So you need to refer(require) commands.js in your index.js file.
You can however import commands.js module directly in your test file but then you need to include it every test file.
Recommended approach is to include it in index.js file and you are not worried about explicitly refer in your test files.

To expand on #Dinesh Kumar's excellent answer, it's also important you haven't disabled support for the default support file (I know, unfortunate naming scheme in this case) inside your cypress.json by adding the line: supportFile: false.
Delete that line from your cypress.json if it's there. You can also specify a different path if you're not happy using the default path of cypress/support/index.js.
Working index.js with commands.js file - both in the support folder:
// index.js
const customCommands = require('./commands.js')
module.exports = {
commands: customCommands
}
And double check your settings:
// cypress.json
{
"baseUrl": "http://demo.your-domain.test",
"supportFile": false, // <-- delete this line present
...
}

It may help to put a line import './commands.js' into index.js.

For me it worked when I added the type signature of the custom command in the file cypress/support/index.d.ts. For more information visit: Cypress example - Custom Commands
declare namespace Cypress {
interface Chainable {
clearLocalStorageIframe(): void
}
}
I am using 7.2.0 Cypress and command.ts and index.ts file extension I have changed it to .ts

TL;DR: Check if your IDE tried to resolve cy
I slipped into this problem, because my IDE's autocomplete feature added a dependency to resolve the undeclared cy object – that gets injected by cypress.
const { default: cy } = require('date-fns/esm/locale/cy/index.js');
This was very unfortunate, as there is an ongoing (in 2022) issue with the custom commands and you can find a tons of hints..

Removing
import { cy } from "date-fns/locale";
or similar import
from the test file, resolved this. This gets added automatically to resolve undeclared cy objects
Permanent Solution: Add the following to cypress.json
"compilerOptions": {
"types": ["cypress"]
}

I added at the top of commands.js.
/// <reference types="cypress" />
export{}
//CUSTOM COMMANDS...
This then exported and exposed the custom commands after cy. .

How to create QUnit tests with reference to another class?

I'm trying to add unit testing for JavaScript into my web site. I use VS2013 and my project is an ASP.NET web site.
Based on recommendations (http://www.rhyous.com/2013/02/20/creating-a-qunit-test-project-in-visual-studio-2010/) I've done so far:
Created new ASP.NET app
Imported QUnit (using NuGet)
Into "Scripts" added links to js-file in my original web site (files PlayerSkill.js - containts PlayerSkill class and trainings.js - contains Trainer and some other classes)
Created new folder "TestScripts"
Added TrainingTests.js file
Wrote simple test:
test( "Trainer should have non-empty group", function () {
var group = "group";
var trainer = new Trainer(123, "Name123", group, 123);
EQUAL(trainer.getTrainerGroup(), group);
});
Notice: my trainings.js file among others contains
function Trainer(id, name, group, level) {
...
var _group = group;
this.getTrainerGroup = function () { return _group ; }
};
When I execute my test I see error: Trainer is not defined.
It looks like reference to my class is not recognized. I feel like linking file is not enough, but what did I miss?
Please help add reference to the original file with class and run unit test.
Thank you.
P.S. Question 2: Can I add reference to 2 files (my unit test will require one more class which is in another file)? How?

You should add all the relevant logic of your application to your unit testing file so they all execute before you run your tests
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>QUnit Test Results</title>
<link rel="stylesheet" href="/Content/qunit.css">
</head>
<body>
<div id="qunit"></div>
<div id="qunit-fixture"></div>
<script src="/Scripts/qunit.js"></script>
<script src="/Scripts/PlayerSkill.js"></script>
<script src="/Scripts/trainings.js"></script>
<script src="/TestScripts/TrainingTests.js"></script>
</body>
</html>
You should not use linked files because they will not exist physically in the script folder.
If you really want to use them you should let the Visual Studio intellisense resolve the physical path of the file like this.
Type the script tag <script src=""></script>
Place the cursor inside the quotes in the src attribute and press CTRL + SPACE
Search your files and let the resolved path untouched
If your project location changes you must update the linked files and also the script references.
{Edit1}
Solution 2:
You could also use an MVC Controller and a Razor View to create your unit testing page and the linked files will work as expected with the only issue that you will have an extra controller in your project but this is not bad at all if for example you want to test the loading of content using ajax that is by default blocked by the browser if they are run from a local file.
Solution 3:
You can also setup a new MVC project just for your javascript unit testing just as you usually setup a new project for any server side code and this will help to prevent your testing to interfere with your production code
{Edit 2}
Solution 4:
As part of the javascript ecosystem you could use grunt or gulp to automate the copy of your scripts from anywhere to your project before running the tests. You could write a gulpfile.js like this
var sourcefiles = [/*you project file paths*/];
gulp.task('default', function () {
return gulp.src(sourcefiles).pipe(gulp.dest('Scripts'));
});
And then run it opening a console and running the command gulp or gulp default

Looks like trainings.js is not defined when calling TrainingTests.js . See this question for more details regarding why this happens! Once that is fixed it does work. And yes similar to trainings.js you can have any number of files in any folder as long as you reference them properly. I have created a sample fiddle accessible # http://plnkr.co/edit/PnqVebOzmPpGu7x2qWLs?p=preview
<body>
<div id="qunit"></div>
<div id="qunit-fixture"></div>
<script src="http://code.jquery.com/qunit/qunit-1.18.0.js"></script>
<script src="trainings.js"></script>
<script src="TrainingTests.js"></script>
</body>

In my case I wanted to run my tests from within my ASP.NET web application, and also on a CI server. In addition to the other information here I needed the following, otherwise I experienced the same error as the OP on my CI server:
Add one or more require() calls to test scripts.
Set the NODE_PATH environment variable to the root of my application.
Example of require()
Within my test scripts I include a requires block, the conditional allows me to use this script from a web browser without needing to adopt a third-party equivalent such as requirejs (which is convenient.)
if (typeof(require) !== 'undefined') {
require('lib/3rdparty/dist/3p.js');
require('js/my.js');
require('js/app.js');
}
Example of setting NODE_PATH
Below, 'wwwroot' is the path of where /lib/ and other application files are located. My test files are located within /tests/.
Using bash
#!/bin/bash
cd 'wwwroot'
export NODE_PATH=`pwd`
qunit tests
Using powershell
#!/usr/bin/pwsh
cd 'wwwroot'
$env:NODE_PATH=(pwd)
qunit tests
This allowed me to run tests both within my ASP.NET web application, and also from a CI server using a script.
HTH.

If you're wondering how to make your tests see your code when running from command line (not from browser!), here is a bit expanded version of Shaun Wilson's answer (which doesn't work out-of-the-box, but contains a good idea where to start)
Having following structure:
project
│ index.js <--- Your script with logic
└───test
tests.html <--- QUnit tests included in standard HTML page for "running" locally
tests.js <--- QUnit test code
And let's imagine that in your index.js you have following:
function doSomething(arg) {
// do smth
return arg;
}
And the test code in tests.js (not that it can be the whole content of the file - you don't need anything else to work):
QUnit.test( "test something", function( assert ) {
assert.ok(doSomething(true));
});
Running from command line
To make your code accessible from the tests you need to add two things to the scripts.
First is to explicitly "import" your script from tests. Since JS doesn't have sunch a functionality out-of-the box, we'll need to use require coming from NPM. And to keep our tests working from HTML (when you run it from browser, require is undefined) add simple check:
// Add this in the beginning of tests.js
// Use "require" only if run from command line
if (typeof(require) !== 'undefined') {
// It's important to define it with the very same name in order to have both browser and CLI runs working with the same test code
doSomething = require('../index.js').doSomething;
}
But if index.js does not expose anything, nothing will be accessible. So it's required to expose functions you want to test explicitly (read more about exports). Add this to index.js:
//This goes to the very bottom of index.js
if (typeof module !== 'undefined' && module.exports) {
exports.doSomething = doSomething;
}
When it's done, just type
qunit
And the output should be like
TAP version 13
ok 1 Testing index.js > returnTrue returns true
1..1
# pass 1
# skip 0
# todo 0
# fail 0

Well, due to help of two answers I did localize that problem indeed was in inability of VS to copy needed file into test project.
This can be probably resolved by multiple ways, I found one, idea copied from: http://www.javascriptkit.com/javatutors/loadjavascriptcss.shtml
Solution is simple: add tag dynamically
In order to achieve this, I've added the following code into tag:
<script>
var fileref = document.createElement('script');
fileref.setAttribute("type", "text/javascript");
var path = 'path'; // here is an absolute address to JS-file on my web site
fileref.setAttribute("src", path);
document.getElementsByTagName("head")[0].appendChild(fileref);
loadjscssfile(, "js") //dynamically load and add this .js file
</script>
And moved my tests into (required also reference to jquery before)
$(document).ready(function () {
QUnit.test("Test #1 description", function () { ... });
});
Similar approach also works for pure test files.

JavaScript require() on client side

Is it possible to use require() (or something similar) on client side?
Example
var myClass = require('./js/myclass.js');

You should look into require.js or head.js for this.

I've been using browserify for that. It also lets me integrate Node.js modules into my client-side code.
I blogged about it here: Add node.js/CommonJS style require() to client-side JavaScript with browserify

If you want to have Node.js style require you can use something like this:
var require = (function () {
var cache = {};
function loadScript(url) {
var xhr = new XMLHttpRequest(),
fnBody;
xhr.open('get', url, false);
xhr.send();
if (xhr.status === 200 && xhr.getResponseHeader('Content-Type') === 'application/x-javascript') {
fnBody = 'var exports = {};\n' + xhr.responseText + '\nreturn exports;';
cache[url] = (new Function(fnBody)).call({});
}
}
function resolve(module) {
//TODO resolve urls
return module;
}
function require(module) {
var url = resolve(module);
if (!Object.prototype.hasOwnProperty.call(cache, url)) {
loadScript(url);
}
return cache[url];
}
require.cache = cache;
require.resolve = resolve;
return require;
}());
Beware: this code works but is incomplete (especially url resolving) and does not implement all Node.js features (I just put this together last night).
YOU SHOULD NOT USE THIS CODE in real apps but it gives you a starting point. I tested it with this simple module and it works:
function hello() {
console.log('Hello world!');
}
exports.hello = hello;

I asked myself the very same questions. When I looked into it I found the choices overwhelming.
Fortunately I found this excellent spreadsheet that helps you choice the best loader based on your requirements:
https://spreadsheets.google.com/lv?key=tDdcrv9wNQRCNCRCflWxhYQ

Take a look at requirejs project.

I have found that in general it is recommended to preprocess scripts at compile time and bundle them in one (or very few) packages with the require being rewritten to some "lightweight shim" also at compile time.
I've Googled out following "new" tools that should be able to do it
http://mixu.net/gluejs/
https://github.com/jrburke/almond
https://github.com/component/builder2.js
And the already mentioned browserify should also fit quite well - http://esa-matti.suuronen.org/blog/2013/04/15/asynchronous-module-loading-with-browserify/
What are the module systems all about?
Older Stack Overflow explanation - Relation between CommonJS, AMD and RequireJS?
Detailed discussion of various module frameworks and the require() they need is in Addy Osmani - Writing Modular JavaScript With AMD, CommonJS & ES Harmony

You can create elements to the DOM, which loads items.
Like such:
var myScript = document.createElement('script'); // Create new script element
myScript.type = 'text/javascript'; // Set appropriate type
myScript.src = './js/myclass.js'; // Load javascript file

Simply use Browserify, what is something like a compiler that process your files before it go into production and packs the file in bundles.
Think you have a main.js file that require the files of your project, when you run browserify in it, it simply process all and creates a bundle with all your files, allowing the use of the require calls synchronously in the browser without HTTP requests and with very little overhead for the performance and for the size of the bundle, for example.
See the link for more info: http://browserify.org/

Some answers already - but I would like to point you to YUI3 and its on-demand module loading. It works on both server (node.js) and client, too - I have a demo website using the exact same JS code running on either client or server to build the pages, but that's another topic.
YUI3: http://developer.yahoo.com/yui/3/
Videos: http://developer.yahoo.com/yui/theater/
Example:
(precondition: the basic YUI3 functions in 7k yui.js have been loaded)
YUI({
//configuration for the loader
}).use('node','io','own-app-module1', function (Y) {
//sandboxed application code
//...
//If you already have a "Y" instance you can use that instead
//of creating a new (sandbox) Y:
// Y.use('moduleX','moduleY', function (Y) {
// });
//difference to YUI().use(): uses the existing "Y"-sandbox
}
This code loads the YUI3 modules "node" and "io", and the module "own-app-module1", and then the callback function is run. A new sandbox "Y" with all the YUI3 and own-app-module1 functions is created. Nothing appears in the global namespace. The loading of the modules (.js files) is handled by the YUI3 loader. It also uses (optional, not show here) configuration to select a -debug or -min(ified) version of the modules to load.

Here's a solution that takes a very different approach: package up all the modules into a JSON object and require modules by reading and executing the file content without additional requests.
https://github.com/STRd6/require/blob/master/main.coffee.md
STRd6/require depends on having a JSON package available at runtime. The require function is generated for that package. The package contains all the files your app could require. No further http requests are made because the package bundles all dependencies. This is as close as one can get to the Node.js style require on the client.
The structure of the package is as follows:
entryPoint: "main"
distribution:
main:
content: "alert(\"It worked!\")"
...
dependencies:
<name>: <a package>
Unlike Node a package doesn't know it's external name. It is up to the pacakge including the dependency to name it. This provides complete encapsulation.
Given all that setup here's a function that loads a file from within a package:
loadModule = (pkg, path) ->
unless (file = pkg.distribution[path])
throw "Could not find file at #{path} in #{pkg.name}"
program = file.content
dirname = path.split(fileSeparator)[0...-1].join(fileSeparator)
module =
path: dirname
exports: {}
context =
require: generateRequireFn(pkg, module)
global: global
module: module
exports: module.exports
PACKAGE: pkg
__filename: path
__dirname: dirname
args = Object.keys(context)
values = args.map (name) -> context[name]
Function(args..., program).apply(module, values)
return module
This external context provides some variable that modules have access to.
A require function is exposed to modules so they may require other modules.
Additional properties such as a reference to the global object and some metadata
are also exposed.
Finally we execute the program within the module and given context.
This answer will be most helpful to those who wish to have a synchronous node.js style require statement in the browser and are not interested in remote script loading solutions.

I find the component project giving a much more streamlined workflow than other solutions (including require.js), so I'd advise checking out https://github.com/component/component . I know this is a bit late answer but may be useful to someone.

Here's a light weight way to use require and exports in your web client. It's a simple wrapper that creates a "namespace" global variable, and you wrap your CommonJS compatible code in a "define" function like this:
namespace.lookup('org.mydomain.mymodule').define(function (exports, require) {
var extern = require('org.other.module');
exports.foo = function foo() { ... };
});
More docs here:
https://github.com/mckoss/namespace

The clientside-require library provides an asynchronous load() function that can be used to load any JS file or NPM module (which uses module.exports), any .css file, any .json, any .html, any any other file as text.
e.g.,
npm install clientside-require --save
<script src = '/node_modules/clientside-require/dist/bundle.js'></script>
<script>
load('color-name') // an npm module
.then(color_name=>{
console.log(color_name.blue); // outputs [0, 0, 255]
})
</script>
A really cool part of this project is that inside of any load()ed script, you can use the synchronous require() function the same way you would expect in node.js!
e.g.,
load('/path/to/functionality.js')
and inside /path/to/functionality.js:
var query_string = require("qs") // an npm module
module.exports = function(name){
return qs.stringify({
name:name,
time:new Date()
}
}
That last part, implementing the synchronous require() method, is what enables it to utilize NPM packages built to run on the server.
This module was designed to implement the require functionality as closely as possible in the browser. Disclaimer: I have written this module.

Yes it is very easy to use, but you need to load javascript file in browser by script tag
<script src="module.js"></script>
and then user in js file like
var moduel = require('./module');
I am making a app using electron and it works as expected.