Understanding the wss.clients object in the ws npm package - javascript

I am working with the npm ws library on a Node.js server. I was looking at the documentation and found a way to loop through the clients to, for example, send a message to everyone using the wss.clients object:
const WebSocket = require('ws');
const wss = new WebSocket.server({ port:8080 });
//...
wss.clients.forEach(client => {
client.send("A message to you!");
});
I initially thought that wss.clients was an array because it let me iterate through it with the array prototype forEach(), but when I tried running wss.clients.find() on it to send a message only to a specific connection, I got an error:
TypeError: wss.clients.find is not a function
I ran console.log(Array.isArray(wss.clients)) it said false. When I tried console.log(wss.clients), I got an object looking like this:
Set { WebSocket { ... } }
So, my question is, how is the wss.clients object able to run the array prototype forEach()? It worked without using Object.keys() or anything.
I also tried wss.clients.pop() out of curiosity, and it gave another type error.
What really is wss.clients? An object or an array?

I have discovered (thanks to #waiaan) that the type of wss.clients is a Set.
Sets have different methods than arrays, but they are similar.
The best implementation for Set.prototype.find() would be to define a method like this:
Set.prototype.find = function(cb) {
for (const e of this) {
if (cb(e)) {
return e;
}
}
}
More about arrays and sets in this article.

Related

TypeError: Class method is not a function, confused about binding this

I have this class Game.
class Game {
constructor(player) {
this.player1 = player;
}
getHost() {
// player has property nickname
return `Host: ${this.player1.nickname}`;
}
}
I believe the issue I am having is that getHost() is becoming unbound from it's context, however I'm not sure how to fix it. I'm learning JS and I'm pretty confused about this language's usage of this. I'm also using socket.io for the first time, so this adds a lot to the confusion for me.
My server script (the server works, just showing relevant parts):
io.on('connection', (socket) => {
// passed defined player
socket.on('host game', (player) => {
const game = new Game(player);
console.log(game.getHost()); // still works here
io.sockets.emit("game created", game);
});
});
Client:
socket.on("game created", (game) => {
const gameElement = document.createElement("li");
gameElement.innerHTML = game.getHost(); // ERROR
games.appendChild(gameElement);
});
On the above marked line, I get the Uncaught TypeError: game.getHost is not a function.
Sorry if the socket.io functions make it more confusing, basically just when the game is passed from server to client, it doesn't work anymore.
Thanks for the help
The issue is that socketio is serializing the object for you. Since a websocket is still just HTTP, you can't send an actual JS object over it. socketio handles serializing your object to JSON using JSON.stringify(game) behind the scenes. It will also convert that JSON string back into an object for you on the client side too.
Unfortunately when you do this you lose methods. For example:
let game = new Game({nickname: 'Bob Vance'});
game = JSON.stringify(game);
console.log(game) // will output {"player1":{"nickname":"Bob Vance"}}
You should see {"player1":{"nickname":"Bob Vance"}} in the console because serializing to JSON drops the methods but preserves properties. This is just normal JavaScript behaviour.
So what you have to do to get the methods back is create a new instance of a game on the client-side, and then use Object.assign() to build the object back up.
Example
let serializedGame= JSON.parse(game);
let newGameInstance = new Game({nickname: game.nickname});
Object.assign(newGameInstance, serializedGame);
Now you should be ok to call newGameInstance.getHost()

How to fix 'variable is not constructor' error in discord.js node project?

i'm experemeting with discord bot and tried to create record in database, but there's some troubles with it.
mongodb server is running and fully functioning.
there's two files.
first, with code of command:
https://sourceb.in/6834bfe20e.js
and second. with mongoose scheme:
https://sourceb.in/9f0c7858df.js
acrually, there's third file index file with command handler and
librarys initializations, but that's does not participate in the error.
I expected to create a record in the database, but there's error what says:
'token is not constructor' in command file:13:19
Problem:
Simply put, you're declaring a constant token, but also passing a parameter named token into your callback. When you're attempting to construct a new object based on the constant, you're actually using the callback's token variable.
Take note of this example, which emits the same error with your setup:
const token = class {
constructor(guild) {
this.guild = guild;
}
};
console.log(new token('1234')); // Works fine.
function foo(token) {
console.log(new token('1234')); // Throws error.
}
foo({ someOtherVar: true });
Solution:
A quick rename of your variable(s) will do. I'd suggest naming your const tokenSchema to avoid conflict (and confusion).

Store and retrieve Google Dart objects in JavaScript library containers

Store and retrieve Google Dart objects in JavaScript library containers
In a Dart application I am using an external JavaScript library to do various matrix calculations.
The specific functionality of the library is not important, what it's important is that I need to store and retrieve Dart object that I put in the matrix.
Dart Class - Lets image i have a dart object that which has a parameter called name
MyDartClass mydc = new MyDartClass(something, something);
mydc.name;
// Everything works as planned
Storing
matrix = js.context.matrix
matrix.cell(1,1).store("thing", new MyDartClass(something, something));
Retrieving
matrix.cell(1,1).has_object_of_type("thing");
// true
MyDartClass mydc = matrix.cell(1,1).retrieve("thing");
Do something with the object
mydc.name;
// Exception: The null object does not have a getter 'name'.
// NoSuchMethodError : method not found: 'name'
// Receiver: null
// Arguments: []
Does the library really work?
Yes it does. I have done the exact same thing in pure javascript many times and there are plenty of test to test the behaviour ( in Javascript )
Is Dart Broken?
When I try to use a javascriptified Hash to do the same behavoiur it works like a charm.
var options = js.map({ 'dart' : new MyDartclass(something, something));
var y = options["dart"];
js.context.console.log(y.name);
// Name is printed
What do you get out from the retrieve?
It seems that I get some kind of Dart Proxy
MyDartClass mydc = matrix.cell(1,1). retrieve("thing");
js.context.console.log(mydc);
DartProxy {id: "dart-ref-20", port: DartSendPortSync}
id: "dart-ref-20"
port: DartSendPortSync
__proto__: DartProxy
I belive that the lib stores the objects, deep down, in a hash map. But it seems like when I retrieve the object into the Dart I get something, but not in a way that I can work with it. So i need help since I don't know how to make it work.
Do I need to de-proxify the object?
Perhaps it IS a Dart bug when you try to retrieve objects from hashes inside objects
Perhaps I missunderstod everything that this is not suppose to work.
Passing and retrieving Dart objects inside the same scope is working. There's the following test case in the tests of js-interop to proove it :
test('retrieve same dart Object', () {
final date = new DateTime.now();
js.context.dartDate = date;
expect(js.context.dartDate, equals(date));
});
However there seems to be an issue with multiple scopes (and multiple event loops as well). There is no way to retain a dart object for now. So your dart object reference goes away at the end of scope. Here's a simple test case that fails :
test('retrieve same dart Object', () {
final date = new DateTime.now();
js.scoped(() {
js.context.dartDate = date;
});
js.scoped(() {
expect(js.context.dartDate, equals(date));
});
});
Please file an issue.

Async.forEach iterator data formatting issue

I am having an issue with the Mongoose fixture loader and I am not sure what is wrong.
When I load my data according to docs such as:
var data = { User: [{name: 'Alex'}, {name: 'Bob'}] };
It does not load. Exploring the code I see that in this file there is an async.forEach iterator which doesn't seem to get triggered. Creating a simple file to test I still cannot get this to work as it should. Evidently the console should print 'User' but it does not. Can someone shed some light on what the issue might be? Note that while I have phrased my question about the async, ultimately I am trying to get the mongoose loader to work so I need to stay within their code structure.
var async = require('async');
var data = { User: [{name: 'Alex'}, {name: 'Bob'}] };
var iterator = function(modelName, next){
// not working
console.log(modelName);
next();
};
async.forEach(data, iterator, function() { });
The pow-mongoose-fixtures module in the NPM repository contains a bug (see bug report).
Your code contains the same bug:
async.forEach(data, ...)
forEach() operates on arrays, but data is an object. In case of the module, it was fixed by using Object.keys() to get an array of keys. You could use it too:
async.forEach(Object.keys(data), ...);
To get mongoose-fixtures working, install the GitHub version:
npm install git://github.com/powmedia/mongoose-fixtures.git
There's a couple of changed you need to make to your code as well:
var fixtures = require('mongoose-fixtures'); // renamed from 'pow-mongoose-fixtures'
var client = mongoose.connect(...);
...
fixtures.load(data, client); // need to pass the client object

Question about socket.io event hook up in the following code

In the node.js/socket.io code accompanying this article the following code is used to hook up events:
socket.on('message', function(message) {
var handler = messageFactory[message.messageType];
$chatMessages.append(handler(message));
});
What is the logic/effect of referencing messageFactory as an array (or at least using [] symbols)? Does it create different handles for different messageType?
Thanks!
What is the logic/effect of referencing messageFactory as an array (or at least using [] symbols)? Does it create different handles for different messageType?
messageFactory is an object with two methods chat and system.
I would assume message.messageType is either "chat" or "system"
So messageFactory[message.messageType] simply gets one of the two methods.
Then handler(message) calls that method.
This is becuase messageFactory.chat === messageFactory["chat"]
If you take a look at the server file ("Listing 5: The chatRoom module.") you will see methods returning
return {
messageType: 'system',
text: originalNick + ' changed nick to ' + newNick
};
So the server returns a message object with a messageType property thats read on the client, it appears that messageType is only "chat" or "system".
That code is basically the OO Command Design Pattern. It's running a different command based on the type of object returned

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