I see that there are some other questions that seem to be on a similar topic but none have an answer that will help me with my particular problem. I have made a thread library in in JavaScript built around the setTimeout and setInterval functions. This is working very well except that my thread library requires that the name of thread is past to the thread i.e when I instantiate the thread it looks like this.
t = new Thread(payload, "t")
payload is an object that defines the what the thread will do when it gets a chance to execute. This allows me to abstract the task of the thread from the underlying threads "plumbing". In any case my problem that I have to pass name of thread because setTimeout and setInterval take a JavaScript command as a string i.e setTimeout("doStuff", 0). As I use my thread library in more applications passing the name to the thread is becoming more of a pain. So I would like to be able to avoid this by getting the name of the thread from within the thread class like this:
var myThreadName = this.someMagicFunction();
or
var myThreadName = someMagicFunction(this);
or some other fantastic method if anyone has any ideas for me I would be most grateful.
Actually, both can take a function as the first parameter, and this is the recommended usage (since the string versions do an eval).
setTimeout(doStuff, 0);
In your case, you might be able to do something like:
setTimeout(function(){
t.payload();
}, 0);
depending how the Thread object looks.
See the MDC documentation (setTimeout, setInterval).
You can pass a function to setTimeout as long as it is argument-free, i.e.
function takeme()
{
alert('workin?');
}
setTimeout(takeme, 100);
and if it is not, then you can try
function takeme(x)
{
alert(x);
}
var test = 1;
setTimeout(function(){ takeme(test); }, 100);
But if you really need to extract a function name, then please see this post. Not exactly the same, but somewhat related.
Related
I'm trying to debug something live on a customer website and my code is all inside an anonymous function block. I don't know if there's anyway to reach that code to execute functions or look at variables in there. I can't put a breakpoint either because this code is dynamically generated each time the page is refreshed and the breakpoint doesn't stick.
(function() {
var Date = "14 September 2022 14:44:55"; // different every refresh for example
var Holder = {
var Items = {
item1: "Value1",
item2: "Value2"
};
function getItem(name) {
return Items[name];
};
function setItem(name, value) {
Items[name] = value;
};
setTimeout(DoSomething(), 2000);
})();
That's not the actual code, just a bare minimum example to illustrate the problem.
Is there anyway to get reach getItem() or Items?
Without a breakpoint that code probably runs to completion then POOF it's all gone anyway.
Redefine setTimeout
If it really is the case that the code inside the anonymous function calls other browser methods, you might be able to insert a detour at runtime that you can then put a breakpoint on.
For this to work, you will need to be able to inject new code into the page before the anonymous code, because there's no other way to invoke the IIFE.
Your example code uses setTimeout, so here's what I would try to insert:
let realSetTimeout = window.setTimeout
window.setTimeout = (...args) => {
debugger
return realSetTimeout(...args)
}
Lots of unrelated code might be calling setTimeout, in which case this could break the page or just make debugging really tedious. In that case, you might make it only debug if one of the setTimeout args has a value that's used in your example, e.g.:
// only break for our timeout
if(args[1] === 2000) debugger
Something like that might not trigger for only your code, but it would hugely reduce the number of other codepaths that get interrupted on their journey through the commonly-used browser capability.
Alternatively, use Charles Proxy to rewrite the body of the HTML page before it enters your browser. You could manually insert a debugger call directly into the anonymous function. Charles is not free, but I think they have a demo that might let you do this. If you do this professionally, it's probably a good purchase anyway. Your employer might even pay for the license.
If you can't use Charles (or a similar tool), you could instead set up a local proxy server using Node which does the rewrite for you. Something like that might only take an hour to throw together. But that is a bigger task, and deserves its own question if you need help with that.
No unfortunately.
The variables inside of the anonymous object are created in a scope which is inaccessible from the outside.
One of the main benefits of using a closure!
You’ll have to find a way to insert your own code inside of it by modifying the function that is generating those objects. If you can’t do that, then you’ll have to take the fork in the road and find another way.
Context
I'm building a general purpose game playing A.I. framework/library that uses the Monte Carlo Tree Search algorithm. The idea is quite simple, the framework provides the skeleton of the algorithm, the four main steps: Selection, Expansion, Simulation and Backpropagation. All the user needs to do is plug in four simple(ish) game related functions of his making:
a function that takes in a game state and returns all possible legal moves to be played
a function that takes in a game state and an action and returns a new game state after applying the action
a function that takes in a game state and determines if the game is over and returns a boolean and
a function that takes in a state and a player ID and returns a value based on wether the player has won, lost or the game is a draw. With that, the algorithm has all it needs to run and select a move to make.
What I'd like to do
I would love to make use of parallel programming to increase the strength of the algorithm and reduce the time it needs to run each game turn. The problem I'm running into is that, when using Child Processes in NodeJS, you can't pass functions to the child process and my framework is entirely built on using functions passed by the user.
Possible solution
I have looked at this answer but I am not sure this would be the correct implementation for my needs. I don't need to be continually passing functions through messages to the child process, I just need to initialize it with functions that are passed in by my framework's user, when it initializes the framework.
I thought about one way to do it, but it seems so inelegant, on top of probably not being the most secure, that I find myself searching for other solutions. I could, when the user initializes the framework and passes his four functions to it, get a script to write those functions to a new js file (let's call it my-funcs.js) that would look something like:
const func1 = {... function implementation...}
const func2 = {... function implementation...}
const func3 = {... function implementation...}
const func4 = {... function implementation...}
module.exports = {func1, func2, func3, func4}
Then, in the child process worker file, I guess I would have to find a way to lazy load require my-funcs.js. Or maybe I wouldn't, I guess it depends how and when Node.js loads the worker file into memory. This all seems very convoluted.
Can you describe other ways to get the result I want?
child_process is less about running a user's function and more about starting a new thread to exec a file or process.
Node is inherently a single-threaded system, so for I/O-bound things, the Node Event Loop is really good at switching between requests, getting each one a little farther. See https://nodejs.org/en/docs/guides/event-loop-timers-and-nexttick/
What it looks like you're doing is trying to get JavaScript to run multiple threads simultaniously. Short answer: can't ... or rather it's really hard. See is it possible to achieve multithreading in nodejs?
So how would we do it anyway? You're on the right track: child_process.fork(). But it needs a hard-coded function to run. So how do we get user-generated code into place?
I envision a datastore where you can take userFn.ToString() and save it to a queue. Then fork the process, and let it pick up the next unhandled thing in the queue, marking that it did so. Then write to another queue the results, and this "GUI" thread then polls against that queue, returning the calculated results back to the user. At this point, you've got multi-threading ... and race conditions.
Another idea: create a REST service that accepts the userFn.ToString() content and execs it. Then in this module, you call out to the other "thread" (service), await the results, and return them.
Security: Yeah, we just flung this out the window. Whether you're executing the user's function directly, calling child_process#fork to do it, or shimming it through a service, you're trusting untrusted code. Sadly, there's really no way around this.
Assuming that security isn't an issue you could do something like this.
// Client side
<input class="func1"> // For example user inputs '(gamestate)=>{return 1}'
<input class="func2">
<input class="func3">
<input class="func4">
<script>
socket.on('syntax_error',function(err){alert(err)});
submit_funcs_strs(){
// Get function strings from user input and then put into array
socket.emit('functions',[document.getElementById('func1').value,document.getElementById('func2').value,...
}
</script>
// Server side
// Socket listener is async
socket.on('functions',(funcs_strs)=>{
let funcs = []
for (let i = 0; i < funcs_str.length;i++){
try {
funcs.push(eval(funcs_strs));
} catch (e) {
if (e instanceof SyntaxError) {
socket.emit('syntax_error',e.message);
return;
}
}
}
// Run algorithm here
}
Is there any existing api/code for handling and chaining long-running "async" javascript functions?
First of all I don't think there are any such thing as an asynch function in js right? I guess the only asynch api is the http-request that jQuery uses or am I wrong?
Anyway, when using jQuery to first for instance ping a server, then login, then load a bunch of items etc, it's not very pretty to wrap these functions in each others completed-handler if you know what I mean.
What I have done now is to define a Task-class with some kind of linked-list capabilities, with a task.next-property etc. When I chain these and execute task.run on the first, I have designed it so that each task is run and when its completed-handler is called it runs the task.next task etc.
This works fine but I'm wondering is there is any existing more complete apis for this allready out there I should use?
Maybee with support for cancellation, progress, exception-aggregation etc?
Maybee there are plans for similar async/wait tasks as there are in C# now, but in js?
If you are targetting the browser, you can use setTimeout.. and break up your code into functions, with each iteraction taking one off the stack/queue, and doing that part.. there are also web workers...
If you are doing server-side JS (such as NodeJS), then there are libraries to make async tasks easier to manage. In the browser it takes work... You'll essentially want to create a bundle of tasks, and work them..
function processBundle(tasks, callback) {
var hnd = setTimeout(doWork, 20);
function doWork() {
var item = tasks.shift();
item();
return (
tasks.length
? setTimeout(doWork, 20)
: callback()
);
}
}
//using it...
var items = [];
items.push(simpleFunction1);
...
items.push(simpleFunctionN);
processBundle(items, function(){
alert("done!");
});
I need to let a piece of code always run independently of other code. Is there a way of creating a thread in javascript to run this function?
--why setTimeout doesn't worked for me
I tried it, but it runs just a single time. And if I call the function recursively it throws the error "too much recursion" after some time. I need it running every 100 milis (it's a communication with a embedded system).
--as you ask, here goes some code
function update(v2) {
// I removed the use of v2 here for simplicity
dump("update\n"); // this will just print the string
setTimeout(new function() { update(v2); }, 100); // this try doesn't work
}
update(this.v);
It throws "too much recursion".
I am assuming you are asking about executing a function on a different thread. However, Javascript does not support multithreading.
See: Why doesn't JavaScript support multithreading?
The Javascript engine in all current browsers execute on a single thread. As stated in the post above, running functions on a different thread would lead to concurrency issues. For example, two functions modifying a single HTML element simultaneously.
As pointed out by others here, perhaps multi-threading is not what you actually need for your situation. setInterval might be adequate.
However, if you truly need multi-threading, JavaScript does support it through the web workers functionality. Basically, the main JavaScript thread can interact with the other threads (workers) only through events and message passing (strings, essentially). Workers do not have access to the DOM. This avoids any of the concurrency issues.
Here is the web workers spec: http://www.whatwg.org/specs/web-workers/current-work/
A more tutorial treatment: http://ejohn.org/blog/web-workers/
Get rid of the new keyword for the function you're passing to setTimeout(), and it should work.
function update(v2) {
try {
dump("update\n");
} catch(err) {
dump("Fail to update " + err + "\n");
}
setTimeout(function() { update(v2); }, 100);
}
update(this.v);
Or just use setInterval().
function update(v2) {
try {
dump("update\n");
} catch(err) {
dump("Fail to update " + err + "\n");
}
}
var this_v = this.v;
setInterval(function() {update(this_v);}, 100);
EDIT: Referenced this.v in a variable since I don't know what the value of this is in your application.
window.setTimeout() is what you need.
maybe you should to view about the javascirpt Workers (dedicated Web Workers provide a simple means for web content to run scripts in background threads), here a nice article, which explain how this works and how can we to use it.
HTML5 web mobile tutororial
U can try a loop instead of recursivity
I would like to ask if there is a liveconnect equivalent for ActionScript 3. I understand that there is the ExternalInterface class inside AS3 but it only supports calling a method by name. The really cool thing about Java and LiveConnect is that you can do something like
function jsFunc(name) = {
this.name = name;
this.talk = function(){
alert('hello world my name is ' + this.name);
}
}
javaapplet.function(new jsFunc("bob"));
The above approaches pseudo code since I never tested it but I've seen it in action. In AS3, while I am able to pass in an instance of JavaScript "object" into AS, it is often converted into an ActionScript Object instance which does away with all the functions as far as I'm aware.
I saw an implementation of JSInterface but I don't think it does specifically that. Is there any way to make OO like javascript work with ActionScript 3?
Try this library on Google code:
http://code.google.com/p/jsobject/
ExternalInterface.call("f = function() { alert('Is this like live connect?'); }");
Actually the main usage scenario is to have JS "objects" interacting with the Flex SWF application. Therefore when the JS "object" wants to say wait for something happening in the SWF object, it will put in a "this" with a callback.
After researching, the way I used to accomplish this is via the Flex Ajax bridge. It may not be a direct answer to the way I phrased the question but it was sufficient for my needs.
Basically what I do is via FABridge, after initializing, I'll attach event listeners to the object.
// JS
FlexApp.addEventListeners('flexDidSomething', this.doSomething().bind(this)); //using mootools;
and in Flex, the main application itself
// AS
dispatchEvent(new CustomCreatedEvent(param1, param2));
And inside the JS function I'll access the get methods of the event object to retrieve the params.
There's tight coupling in that sense but it works at least for what I need.
Hope this is helpful!
JSInterface designed exactly for such things.