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How to dynamically add function objects to an object function map

Hey there StackOverflow people of the world! Thank you for helping me with my question, and I apologize if this question gets a bit long winded. I just want to be clear about all the details and constraints I am working with. I found a few other related questions but nothing that was really very clear about how to get around my specific problem, unless I am missing something. Related questions:[1, 2]
Question Setup:
This is what I have and how it works, my question will be about a problem I am having
I've got a object that I've filled with named functions. The purpose of the object map is to contain many functions calls from multiple files. I am calling each function a "business rule" and they are typically very small functions that do a singular action with well-defined inputs and outputs. It also lets me chain the function calls sequentially with the output from functionCall1 becoming the input functionCall2.
All of my business rule definitions up to this point have been in a set of files that reside in a sub-folder called "Framework", but what I am trying to do now is allow the "Client" to define their own business rules in their own files and their own object map of function calls. What I would like to do is add all of the function calls to a single shared data storage.
What I am trying to avoid doing:
I am NOT trying to serialize the function calls, neither am I trying to leverage the 'eval' capability of JS. I've tried working with this before and it gets really messy!
Also I DO NOT want to declare a "class" object or use the "this" keyword for this reason:
10-most-common-javascript-mistakes
What is working:
(NOTE: Greatly simplified as I currently have hundreds of "business rules")
// rulesLibrary.js
import * as stringParsing from './Rules/stringParsing';
export const rulesLibrary = {
['Echo']: (inputData, inputMetaData) => (inputData, inputMetaData),
// Business Rules
// ********************************
// StringParsing rules in order
// ********************************
['stringToBoolean']: (inputData, inputMetaData) => stringParsing.stringToBoolean(inputData, inputMetaData),
['stringToDataType']: (inputData, inputMetaData) => stringParsing.stringToDataType(inputData, inputMetaData),
}
// stringParsing.js
export const stringToBoolean = function(inputData, inputMetaData) {
var returnData;
// Function Body...
return returnData;
};
export const stringToDataType = function(inputData, inputMetaData) {
var returnData;
// Function Body...
return returnData;
};
// ruleBroker.js
import * as rules from './rulesLibrary';
export const processRules = function(inputData, inputMetaData, rulesToExecute) {
var returnData = inputData;
for (var rule in rulesToExecute) {
if (rulesToExecute.hasOwnProperty(rule)) {
var key = rule;
var value = rulesToExecute[key];
returnData = rules.rulesLibrary[value](returnData, inputMetaData);
}
}
return returnData;
};
You can see in the code above the rulesLibrary is defining the functions in an object rulesLibrary = {}; which is also exported. Then in the ruleBroker we are calling the associated function:
rules.rulesLibrary[value](returnData, inputMetaData)....and this works great.
My Goal
My goal is to rather than store all these functionName: functionCall on the rules.rulesLibrary, I want to store them on a singleton data storage object I am calling "D".
Here is the definition of "D":
// data.js
export var data = {};
What I have tried - Attempt 1
I first tried to assign all of the contents of the rules.rulesLibrary from the rulesLibrary.js directly to "D" like so in the ruleBroker.js file:
// NOTE: I am actually doing this inside a function so I can boot-strap the rules.rulesLibrary into `D`, before the application begins going about the business of calling business rules via the ruleBroker.
import * as rules from './rulesLibrary';
var D = require('../Resources/data');
D['BusinessRules'] = {};
D['BusinessRules'] = rules.rulesLibrary;
This did not work and attempting to console.log(JSON.stringify(D)); just gave me back:
D{BusinessRules} = {};
What I have tried -- Attempt 2
So I thought maybe I should try and define the business rules map named function calls directly on "D" like so in the rulesLibrary.js file:
// NOTE: I am again doing all of this inside a boot-strap function for the same reason as above.
export const initRulesLibrary = function() {
D['BusinessRules'] = {};
D['BusinessRules'] = {
['Echo']: (inputData, inputMetaData) => (inputData, inputMetaData),
// Business Rules
// ********************************
// StringParsing rules in order
// ********************************
['stringToBoolean']: (inputData, inputMetaData) => stringParsing.stringToBoolean(inputData, inputMetaData),
['stringToDataType']: (inputData, inputMetaData) => stringParsing.stringToDataType(inputData, inputMetaData),
}
};
Again I get the same thing, contents of D are: D{BusinessRules} = {}.
Maybe console.log in combination with JSON.stringify doesn't work with function-objects?
But then again, I do have rules that return a function-object and I have been able to stringify those function-objects in the past with this same code. Granted it's a function-object so I am not expecting it to look pretty when stringified, but that's not the point. The point should be that the function-object exists on 'D' and it clearly does not, what am I missing here? How can I get all my function-objects mapped on 'D' so that I can add/merge more function-object definitions to it?
Ultimately this is what I want to be able to do:
function addClientRules(clientRules) {
Object.assign(D['BusinessRules'], clientRules['BusinessRules']);
};
Such that D now contains all of the system-defined business rules & all of the client defined business rules. Then in the ruleBroker, I would just call whatever business rule like this:
export const processRules = function(inputData, inputMetaData, rulesToExecute) {
var returnData = inputData;
for (var rule in rulesToExecute) {
if (rulesToExecute.hasOwnProperty(rule)) {
var key = rule;
var value = rulesToExecute[key];
// OLD WAY:
// returnData = rules.rulesLibrary[value](returnData, inputMetaData);
// NEW WAY:
returnData = D['BusinessRules'][value](returnData, inputMetaData);
}
}
return returnData;
};
Any ideas? Thoughts? Edits? Rants? Am I at least on the right track?
Thank you again for your help! Hopefully this will help someone else too!! :-D

Turns out I was already doing everything correctly to begin with. It's just that console.log & JSON.stringify don't work well with a object map of functions.
The function maps do contain the function calls, just don't expect your console.log even with JSON.stringify to dump that data in any way. You have to proceed with making the call as if it is there and verify that the execution is successful by putting console logs in the function that calls the rule and additionally putting console logs in the rule that is to be executed.
It does work and it's pretty cool when it does!!
I hope this can help someone else, please comment if you have any additional questions and/or if I can provide additional solution details.
Log of successful execution:
c.ccustomEcho resolves as: customEcho
BEGIN warden.executeBusinessRule function
businessRule is: customEcho
ruleInput is: Calling Custom Echo from application
ruleMetaData is: Calling Custom Echo from application
BEGIN ruleBroker.processRules function
inputData is: "Calling Custom Echo from application"
inputMetaData is: "something-nothing"
rulesToExecute are: {"0":"customEcho"}
BEGIN clientStringParsing.customEcho function
inputData is: Calling Custom Echo from application
inputMetaData is: something-nothing
returnData is: Calling Custom Echo from application clientStringParsing.customEcho
END clientStringParsing.customEcho function
returnData is: "Calling Custom Echo from application clientStringParsing.customEcho"
END ruleBroker.processRules function
returnData is: Calling Custom Echo from application clientStringParsing.customEcho
END warden.executeBusinessRule function
Cheers
~Seth

VSCode module.exports autocomplete doesn't work

Using latest VSCode version 1.30.2 and it doesn't see the functions that are inside the exported module.
this is in model.js
var userModel = mongoose.model('userModel', usersSchema);
userModel.isUsernameTaken = isUsernameTaken;
module.exports = userModel;
function isUsernameTaken(username) {
return userModel.findOne({username:username});
}
and in app.js
var userModel = require('./model');
Now upon typing userModel. in app.js I should see a suggestion for autocompletion of isUsernameTaken, but it's not there and also not any of the functions declared in model are "visible". However if I type the exact function name (case-sensitive). (ex: userModel.isUserNameTaken(etc)) it works. What is wrong ?

I managed to fix it by changing in model.js
module.exports.default = userModel;
and then in another file:
var userModel = require(./model).default;
Now intellisense works as it should.

When you say userModel.isUsernameTaken(username), what you are really saying is mongoose.model('userModel', usersSchema).isUsernameTaken(username), in which this would return as undefined. What you would have to do is make user Model into an object with the mongoose.model('userModel', usersSchema) inside of it. Kind of like this:
var userModel = function () {
this.model: mongoose.model('userModel', usersSchema),
this.isUsernameTaken: (username) => {
return this.model.findOne({username:username});
}
};
Then if you wanted to access these attributes you could use
var user = new userModel(); then use user.isUsernameTaken(/*put username here*/);. Or if you wanted to access the model alone you could do: user.model. I hope this answers your question.

Mock Es6 classes using Jest

I'm trying to mock an ES6 class with a constructor that receives parameters, and then mock different class functions on the class to continue with testing, using Jest.
Problem is I can't find any documents on how to approach this problem. I've already seen this post, but it doesn't resolve my problem, because the OP in fact didn't even need to mock the class! The other answer in that post also doesn't elaborate at all, doesn't point to any documentation online and will not lead to reproduceable knowledge, since it's just a block of code.
So say I have the following class:
//socket.js;
module.exports = class Socket extends EventEmitter {
constructor(id, password) {
super();
this.id = id;
this.password = password;
this.state = constants.socket.INITIALIZING;
}
connect() {
// Well this connects and so on...
}
};
//__tests__/socket.js
jest.mock('./../socket');
const Socket = require('./../socket');
const socket = new Socket(1, 'password');
expect(Socket).toHaveBeenCalledTimes(1);
socket.connect()
expect(Socket.mock.calls[0][1]).toBe(1);
expect(Socket.mock.calls[0][2]).toBe('password');
As obvious, the way I'm trying to mock Socket and the class function connect on it is wrong, but I can't find the right way to do so.
Please explain, in your answer, the logical steps you make to mock this and why each of them is necessary + provide external links to Jest official docs if possible!
Thanks for the help!

Update:
All this info and more has now been added to the Jest docs in a new guide, "ES6 Class Mocks."
Full disclosure: I wrote it. :-)
The key to mocking ES6 classes is knowing that an ES6 class is a function. Therefore, the mock must also be a function.
Call jest.mock('./mocked-class.js');, and also import './mocked-class.js'.
For any class methods you want to track calls to, create a variable that points to a mock function, like this: const mockedMethod = jest.fn();. Use those in the next step.
Call MockedClass.mockImplementation(). Pass in an arrow function that returns an object containing any mocked methods, each set to its own mock function (created in step 2).
The same thing can be done using manual mocks (__mocks__ folder) to mock ES6 classes. In this case, the exported mock is created by calling jest.fn().mockImplementation(), with the same argument described in (3) above. This creates a mock function. In this case, you'll also need to export any mocked methods you want to spy on.
The same thing can be done by calling jest.mock('mocked-class.js', factoryFunction), where factoryFunction is again the same argument passed in 3 and 4 above.
An example is worth a thousand words, so here's the code.
Also, there's a repo demonstrating all of this, here:
https://github.com/jonathan-stone/jest-es6-classes-demo/tree/mocks-working
First, for your code
if you were to add the following setup code, your tests should pass:
const connectMock = jest.fn(); // Lets you check if `connect()` was called, if you want
Socket.mockImplementation(() => {
return {
connect: connectMock
};
});
(Note, in your code: Socket.mock.calls[0][1] should be [0][0], and [0][2] should be [0][1]. )
Next, a contrived example
with some explanation inline.
mocked-class.js. Note, this code is never called during the test.
export default class MockedClass {
constructor() {
console.log('Constructed');
}
mockedMethod() {
console.log('Called mockedMethod');
}
}
mocked-class-consumer.js. This class creates an object using the mocked class. We want it to create a mocked version instead of the real thing.
import MockedClass from './mocked-class';
export default class MockedClassConsumer {
constructor() {
this.mockedClassInstance = new MockedClass('yo');
this.mockedClassInstance.mockedMethod('bro');
}
}
mocked-class-consumer.test.js - the test:
import MockedClassConsumer from './mocked-class-consumer';
import MockedClass from './mocked-class';
jest.mock('./mocked-class'); // Mocks the function that creates the class; replaces it with a function that returns undefined.
// console.log(MockedClass()); // logs 'undefined'
let mockedClassConsumer;
const mockedMethodImpl = jest.fn();
beforeAll(() => {
MockedClass.mockImplementation(() => {
// Replace the class-creation method with this mock version.
return {
mockedMethod: mockedMethodImpl // Populate the method with a reference to a mock created with jest.fn().
};
});
});
beforeEach(() => {
MockedClass.mockClear();
mockedMethodImpl.mockClear();
});
it('The MockedClassConsumer instance can be created', () => {
const mockedClassConsumer = new MockedClassConsumer();
// console.log(MockedClass()); // logs a jest-created object with a mockedMethod: property, because the mockImplementation has been set now.
expect(mockedClassConsumer).toBeTruthy();
});
it('We can check if the consumer called the class constructor', () => {
expect(MockedClass).not.toHaveBeenCalled(); // Ensure our mockClear() is clearing out previous calls to the constructor
const mockedClassConsumer = new MockedClassConsumer();
expect(MockedClass).toHaveBeenCalled(); // Constructor has been called
expect(MockedClass.mock.calls[0][0]).toEqual('yo'); // ... with the string 'yo'
});
it('We can check if the consumer called a method on the class instance', () => {
const mockedClassConsumer = new MockedClassConsumer();
expect(mockedMethodImpl).toHaveBeenCalledWith('bro');
// Checking for method call using the stored reference to the mock function
// It would be nice if there were a way to do this directly from MockedClass.mock
});

For me this kind of Replacing Real Class with mocked one worked.
// Content of real.test.ts
jest.mock("../RealClass", () => {
const mockedModule = jest.requireActual(
"../test/__mocks__/RealClass"
);
return {
...mockedModule,
};
});
var codeTest = require("../real");
it("test-real", async () => {
let result = await codeTest.handler();
expect(result).toMatch(/mocked.thing/);
});
// Content of real.ts
import {RealClass} from "../RealClass";
export const handler = {
let rc = new RealClass({doing:'something'});
return rc.realMethod("myWord");
}
// Content of ../RealClass.ts
export class RealClass {
constructor(something: string) {}
async realMethod(input:string) {
return "The.real.deal "+input;
}
// Content of ../test/__mocks__/RealClass.ts
export class RealClass {
constructor(something: string) {}
async realMethod(input:string) {
return "mocked.thing "+input;
}
Sorry if I misspelled something, but I'm writing it on the fly.

Pass functions in a vm script context

Let's say I have a library module that looks like this:
module.exports = {
increment: function() {
count++;
}
}
And I'd like to use it in a dynamically generated script that looks like this:
(function() { lib.increment(); })();
by passing it in a sandbox:
var sandbox = {
count: 1
lib: require('./lib')
}
var script = new vm.Script('(function() { lib.increment() })();');
script.runInNewContext(sandbox);
The obvious problem I run into is that I on the one hand can't require "lib" because "count" is not defined in lib.js ; on the other hand if I define var count above the exports of the "lib.js" file, this new count variable will be affected instead of the one in the sandbox.
Here are the constraints that I would like to respect:
Use vm and not a eval() nor a require() on a generated file
Have "lib" defined in a external file
No modification of the automatically generated script, so no use of lib.increment.apply(context) or similar
The only solutions I've found so far is to prepend the lib functions in the generated script as a string, or to define them directly on the sandbox object, which I find to be a less desirable option.
There doesn't seem to be any way of passing a context of variables on the require call.

One way of accomplishing this is have your lib module be a function that takes in a context then returns the correct interface.
lib.js
module.exports = function(context) {
var count = context.count;
return {
increment: function() {
count++;
}
};
};
main.js
var sandbox = {
count: 1
};
sandbox.lib = require('./lib')(sandbox);
var script = new vm.Script('(function() { lib.increment() })();');
script.runInNewContext(sandbox);

'TypeError: is not a function' in Node.js

I'm getting the error while running the following code in Node.js
var assert = require('assert');
var request = require('request');
var index = require('./index');
it('verify javascript function', function(done) {
var v2 = index.AddNumbers(5, 6);
assert.equal(11, v2);
done();
});
The index.js file contain the following code:
function AddNumbers(a,b){
return a+b;
}
What am I doing wrong?

This happened to me many times because of circular dependency, check if you have 2 classes that are requiring each other, remove one of them from requiring the other and the issue should be solved

With NodeJS modules, to make something public, you have to export it. Add this to the end of index.js:
module.exports.AddNumbers = AddNumbers;
(That's using the old CommonJS modules. For ESM, it would be export AddNumbers;)
Here it is running on my machine:
$ cat index.js
function AddNumbers(a,b){
return a+b;
}
module.exports.AddNumbers = AddNumbers;
$ cat example.js
var index = require('./index');
var v2 = index.AddNumbers(5,6);
console.log(v2);
$ node example.js
11

I'm fairly a beginner at Node JS so I managed to get this error by importing a function like so:
const { functionName } = require('./function')
instead of like so:
const functionName = require('./function')
Editing my post to add an explanation since I've learned more node since I wrote it. If a module exports an object containing multiple functions functions like so:
module.exports = { functionName, otherFunction }
Then the function has to be deconstructed out of the object during the import, as in the first code snippet. If the module exports a single function or a default function, like so:
module.exports = functionName
Then tt must be imported directly, as in the second code snippet.

If you need to expose a specific component, function or a variable to public. You have to exports those components using JavaScript modules.
let add = (a,b)=>{
return ( a+b);
}
module.exports.add=add;
or if you want to expose multiple functions, you can do as follows.
let add = (a,b)=>{
return (a+b);
}
let subtract = (a, b)=>{
return (a-b);
}
module.exports={
add : add,
subtract : subtract
};

This is happening because two files are referencing each other i.e You are calling function (s) from file A in file B and vice versa which is called Circular Dependency.

Your "AddNumbers" function in the "index.js" file should be as follows,
function AddNumbers(a,b){
var addition = function(a, b){
return (a + b) ;
};
module.exports = {
additionResult: addition
};
}
And you need to call it in your "Node.js" file as follows
var assert = require('assert');
var request = require('request');
var index = require('./index');
it('verify javascript function', function(done) {
var v2 = index.additionResult(5, 6);
assert.equal(11, v2);
done();
});
This should work. Please note that you call the function by whatever the token name you exported the return value by (I use a different name here just for clarity). Almost everybody uses the same name as the function name so there are no confusion. Also in ES6, if you use the same name you can export as just,
module.exports = {
addition
};
instead of,
module.exports = {
addition: addition
};
since you use the same name. It is an ES6 feature.

I ran into the same problem while trying to follow a Nodejs tutorial by w3schools.
I copied the following code from them:
exports.myDateTime = function () {
return Date();
};
That, however, wouldn't work for me. What resolved the problem for me was adding module. before the exports keyword like this:
module.exports.myDateTime = function () {
return Date();
};

The most correct answer was from #shimi_tap. I want to reply it as comment, but doesn't have enough reputation, so I am gonna answer it using a simple example, like in this case below:
File A has 3 functions to process database activity: function
addDB, updateDB, and delData;
File B has 2 functions to process User activity on smartphone:
function addHistory, and editHistory;
Function updateDB in file A is calling function editHis in file B, and function editHistory is calling function updateDB in file A. This is what we called circular-dependency. And we need to prevent it by only giving output of state from editHistory and the rest will be processed inside file A.
//ORIGINAL FUNCTIONS which caused CIRCULAR DEPENDENCY
function updateDB() {
//process update function here
//call function in fileB
const history = require("fileB.js");
await history.editHistory(data).then((output) => {
if(output["message"] === "success"){
response = {
state: 1,
message: "success",
};
}
});
return response;
}
//THIS is the WRONG ONE
function editHistory() {
//process function to edit History here
//call function in fileA
const file = require("fileA.js");
await file.updateDB(data).then((output) => { //You should not call it here
if(output["message"] === "success") {
output = {
state: 1,
message: "success",
};
}
});
return output;
}
//==================================================//
//THE FIX
function updateDB() {
//process function here
const history = require("fileB.js");
await history.editHistory(data).then((output) => {
if(output["message"] === "success"){
await updateDB(data).then((output) => {
response = {
state: 1,
message: "success",
};
});
} else {
log("Error");
}
});
return response;
}
function editHistory() {
//process function to edit History here
// No more calling to function inside the file A
output = {
state: 1,
message: "success",
};
return output;
}

https://medium.com/visual-development/how-to-fix-nasty-circular-dependency-issues-once-and-for-all-in-javascript-typescript-a04c987cf0de
this post visualizes the circular dependency injection
like a child or nested file tried to import parent or top-level file
repo.js
service.js
there are 2 files
service.js uses repo.js file by importing
it works
but check in repo.js that it tried to import service.js file
it shows circular dependency injection warning

In my case the problem was the missing semicolon at the end of the lines.
const codec = JSONCodec()
(async () => {
for await (const message of subscription) {
const payload = codec.decode(message.data)
stompServer.send('/topic/update-event', {}, payload)
}
})()
This produced the following error:
TypeError: JSONCodec(...) is not a function
I was so used to writing code without semicolons, which led me to this problem with the bare NodeJs. As soon as I had put the semicolons, the problem disappeared.

A simple way I debugged this (After about 2 days of troubleshooting) was to actually see why 'x' is not a function. Basically, console.log(x) to see the actual object returned. Turned out I was conflicting x with another declared variable (happens especially when you use axios.res and req,res args.

Require the other file in function level.
fileOne.js
function main() {
const fileTwo = require('./fileTwo');
console.log("hello from file one");
}
module.exports = main;
main();
fileTwo.js
function main() {
const fileOne = require('./fileOne');
console.log("hello from file two");
}
module.exports = main;
main();
Now execute > node fileOne.js
Output:
hello from file two
hello from file one

One silly mistake I did was while exporting was:
module.exports = [module_name_1, module_name_2, ..., module_name_n]
The right way is:
module.exports = {module_name_1, module_name_2, ..., module_name_n}