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Hold on callback function execution until promise is completed

I have some third party library whose events I'm listening. I get a chance to modify data which that library is going to append in the UI. It is all fine until that data modification is synchronous. As soon as I involve Ajax callbacks/promises, this fails to work. Let me put an example to show case the problem.
Below is how I'm listening to a event:-
d.on('gotResults', function (data) {
// If alter data directly it works fine.
data.title = 'newTitle';
// Above code alters the text correctly.
//I want some properties to be grabbed from elsewhere so I make an Ajax call.
$.ajax('http://someurl...', {data.id}, function (res) {
data.someProperty = res.thatProperty;
});
// Above code doesn't wait for ajax call to complete, it just go away and
renders page without data change.
// Yes I tried promises but doesn't help
return fetch('http://someurl...').then(function (data) {
data.someProperty = res.thatProperty;
return true;
});
// Above code also triggers the url and gets away. Doesn't wait for then to complete.
});
I cannot change/alter the third party library. All I have is to listen to event and alter that data.
Any better solutions. Nope. I can't use async/wait, generators, because I want to have it supported for ES5 browsers.

You cannot make a synchronous function wait for an asynchronous response, it's simply not possible by definition. Your options pretty much are:
BAD IDEA: Make a synchronous AJAX request. Again: BAD IDEA. Not only will this block the entire browser, it is also a deprecated practice and should not be used in new code, or indeed ever.
Fetch the asynchronous data first and store it locally, so it's available synchronously when needed. That obviously only works if you have an idea what data you'll be needing ahead of time.
Alter the 3rd party library to add support for asynchronous callbacks, or request that of the vendor.
Find some hackaround where you'll probably let the library work with incomplete data first and then update it when the asynchronous data is available. That obviously depends a lot on the specifics of that library and the task being done.

Does the gotResults callback function really need to return anything else than true? If not, then you could just write regular asynchronous code without this library knowing about it. Let me explain myself by rewriting your pseudocode:
d.on('gotResults', function (data) {
// If alter data directly it works fine.
data.title = 'newTitle';
// Above code alters the text correctly.
//I want some properties to be grabbed from elsewhere so I make an Ajax call.
$.ajax('http://someurl...', {data.id}, function (res) {
data.someProperty = res.thatProperty;
// Above code doesn't wait for ajax call to complete, it just go away and
// EDIT: now it should render properly
renders page without data change.
// Yes I tried promises but doesn't help
return fetch('http://someurl...');
// Above code also triggers the url and gets away. Doesn't wait for then to complete.
}).then(function (data) {
data.someProperty = res.thatProperty;
// maybe render again here?
}).catch(function(err) {
handleError(err); // handle errors so the don't disappear silently
});
return true; // this line runs before any of the above asynchronous code but do we care?
});

Returning Chrome storage API value without function

For the past two days I have been working with chrome asynchronous storage. It works "fine" if you have a function. (Like Below):
chrome.storage.sync.get({"disableautoplay": true}, function(e){
console.log(e.disableautoplay);
});
My problem is that I can't use a function with what I'm doing. I want to just return it, like LocalStorage can. Something like:
var a = chrome.storage.sync.get({"disableautoplay": true});
or
var a = chrome.storage.sync.get({"disableautoplay": true}, function(e){
return e.disableautoplay;
});
I've tried a million combinations, even setting a public variable and setting that:
var a;
window.onload = function(){
chrome.storage.sync.get({"disableautoplay": true}, function(e){
a = e.disableautoplay;
});
}
Nothing works. It all returns undefined unless the code referencing it is inside the function of the get, and that's useless to me. I just want to be able to return a value as a variable.
Is this even possible?
EDIT: This question is not a duplicate, please allow me to explain why:
1: There are no other posts asking this specifically (I spent two days looking first, just in case).
2: My question is still not answered. Yes, Chrome Storage is asynchronous, and yes, it does not return a value. That's the problem. I'll elaborate below...
I need to be able to get a stored value outside of the chrome.storage.sync.get function. I -cannot- use localStorage, as it is url specific, and the same values cannot be accessed from both the browser_action page of the chrome extension, and the background.js. I cannot store a value with one script and access it with another. They're treated separately.
So my only solution is to use Chrome Storage. There must be some way to get the value of a stored item and reference it outside the get function. I need to check it in an if statement.
Just like how localStorage can do
if(localStorage.getItem("disableautoplay") == true);
There has to be some way to do something along the lines of
if(chrome.storage.sync.get("disableautoplay") == true);
I realize it's not going to be THAT simple, but that's the best way I can explain it.
Every post I see says to do it this way:
chrome.storage.sync.get({"disableautoplay": true, function(i){
console.log(i.disableautoplay);
//But the info is worthless to me inside this function.
});
//I need it outside this function.

Here's a tailored answer to your question. It will still be 90% long explanation why you can't get around async, but bear with me — it will help you in general. I promise there is something pertinent to chrome.storage in the end.
Before we even begin, I will reiterate canonical links for this:
After calling chrome.tabs.query, the results are not available
(Chrome specific, excellent answer by RobW, probably easiest to understand)
Why is my variable unaltered after I modify it inside of a function? - Asynchronous code reference (General canonical reference on what you're asking for)
How do I return the response from an asynchronous call?
(an older but no less respected canonical question on asynchronous JS)
You Don't Know JS: Async & Performance (ebook on JS asynchronicity)
So, let's discuss JS asynchonicity.
Section 1: What is it?
First concept to cover is runtime environment. JavaScript is, in a way, embedded in another program that controls its execution flow - in this case, Chrome. All events that happen (timers, clicks, etc.) come from the runtime environment. JavaScript code registers handlers for events, which are remembered by the runtime and are called as appropriate.
Second, it's important to understand that JavaScript is single-threaded. There is a single event loop maintained by the runtime environment; if there is some other code executing when an event happens, that event is put into a queue to be processed when the current code terminates.
Take a look at this code:
var clicks = 0;
someCode();
element.addEventListener("click", function(e) {
console.log("Oh hey, I'm clicked!");
clicks += 1;
});
someMoreCode();
So, what is happening here? As this code executes, when the execution reaches .addEventListener, the following happens: the runtime environment is notified that when the event happens (element is clicked), it should call the handler function.
It's important to understand (though in this particular case it's fairly obvious) that the function is not run at this point. It will only run later, when that event happens. The execution continues as soon as the runtime acknowledges 'I will run (or "call back", hence the name "callback") this when that happens.' If someMoreCode() tries to access clicks, it will be 0, not 1.
This is what called asynchronicity, as this is something that will happen outside the current execution flow.
Section 2: Why is it needed, or why synchronous APIs are dying out?
Now, an important consideration. Suppose that someMoreCode() is actually a very long-running piece of code. What will happen if a click event happened while it's still running?
JavaScript has no concept of interrupts. Runtime will see that there is code executing, and will put the event handler call into the queue. The handler will not execute before someMoreCode() finishes completely.
While a click event handler is extreme in the sense that the click is not guaranteed to occur, this explains why you cannot wait for the result of an asynchronous operation. Here's an example that won't work:
element.addEventListener("click", function(e) {
console.log("Oh hey, I'm clicked!");
clicks += 1;
});
while(1) {
if(clicks > 0) {
console.log("Oh, hey, we clicked indeed!");
break;
}
}
You can click to your heart's content, but the code that would increment clicks is patiently waiting for the (non-terminating) loop to terminate. Oops.
Note that this piece of code doesn't only freeze this piece of code: every single event is no longer handled while we wait, because there is only one event queue / thread. There is only one way in JavaScript to let other handlers do their job: terminate current code, and let the runtime know what to call when something we want occurs.
This is why asynchronous treatment is applied to another class of calls that:
require the runtime, and not JS, to do something (disk/network access for example)
are guaranteed to terminate (whether in success or failure)
Let's go with a classic example: AJAX calls. Suppose we want to load a file from a URL.
Let's say that on our current connection, the runtime can request, download, and process the file in the form that can be used in JS in 100ms.
On another connection, that's kinda worse, it would take 500ms.
And sometimes the connection is really bad, so runtime will wait for 1000ms and give up with a timeout.
If we were to wait until this completes, we would have a variable, unpredictable, and relatively long delay. Because of how JS waiting works, all other handlers (e.g. UI) would not do their job for this delay, leading to a frozen page.
Sounds familiar? Yes, that's exactly how synchronous XMLHttpRequest works. Instead of a while(1) loop in JS code, it essentially happens in the runtime code - since JavaScript cannot let other code execute while it's waiting.
Yes, this allows for a familiar form of code:
var file = get("http://example.com/cat_video.mp4");
But at a terrible, terrible cost of everything freezing. A cost so terrible that, in fact, the modern browsers consider this deprecated. Here's a discussion on the topic on MDN.
Now let's look at localStorage. It matches the description of "terminating call to the runtime", and yet it is synchronous. Why?
To put it simply: historical reasons (it's a very old specification).
While it's certainly more predictable than a network request, localStorage still needs the following chain:
JS code <-> Runtime <-> Storage DB <-> Cache <-> File storage on disk
It's a complex chain of events, and the whole JS engine needs to be paused for it. This leads to what is considered unacceptable performance.
Now, Chrome APIs are, from ground up, designed for performance. You can still see some synchronous calls in older APIs like chrome.extension, and there are calls that are handled in JS (and therefore make sense as synchronous) but chrome.storage is (relatively) new.
As such, it embraces the paradigm "I acknowledge your call and will be back with results, now do something useful meanwhile" if there's a delay involved with doing something with runtime. There are no synchronous versions of those calls, unlike XMLHttpRequest.
Quoting the docs:
It's [chrome.storage] asynchronous with bulk read and write operations, and therefore faster than the blocking and serial localStorage API.
Section 3: How to embrace asynchronicity?
The classic way to deal with asynchronicity are callback chains.
Suppose you have the following synchronous code:
var result = doSomething();
doSomethingElse(result);
Suppose that, now, doSomething is asynchronous. Then this becomes:
doSomething(function(result) {
doSomethingElse(result);
});
But what if it's even more complex? Say it was:
function doABunchOfThings() {
var intermediate = doSomething();
return doSomethingElse(intermediate);
}
if (doABunchOfThings() == 42) {
andNowForSomethingCompletelyDifferent()
}
Well.. In this case you need to move all this in the callback. return must become a call instead.
function doABunchOfThings(callback) {
doSomething(function(intermediate) {
callback(doSomethingElse(intermediate));
});
}
doABunchOfThings(function(result) {
if (result == 42) {
andNowForSomethingCompletelyDifferent();
}
});
Here you have a chain of callbacks: doABunchOfThings calls doSomething immediately, which terminates, but sometime later calls doSomethingElse, the result of which is fed to if through another callback.
Obviously, the layering of this can get messy. Well, nobody said that JavaScript is a good language.. Welcome to Callback Hell.
There are tools to make it more manageable, for example Promises and async/await. I will not discuss them here (running out of space), but they do not change the fundamental "this code will only run later" part.
Section TL;DR: I absolutely must have the storage synchronous, halp!
Sometimes there are legitimate reasons to have a synchronous storage. For instance, webRequest API blocking calls can't wait. Or Callback Hell is going to cost you dearly.
What you can do is have a synchronous cache of the asynchronous chrome.storage. It comes with some costs, but it's not impossible.
Consider:
var storageCache = {};
chrome.storage.sync.get(null, function(data) {
storageCache = data;
// Now you have a synchronous snapshot!
});
// Not HERE, though, not until "inner" code runs
If you can put ALL your initialization code in one function init(), then you have this:
var storageCache = {};
chrome.storage.sync.get(null, function(data) {
storageCache = data;
init(); // All your code is contained here, or executes later that this
});
By the time code in init() executes, and afterwards when any event that was assigned handlers in init() happens, storageCache will be populated. You have reduced the asynchronicity to ONE callback.
Of course, this is only a snapshot of what storage looks at the time of executing get(). If you want to maintain coherency with storage, you need to set up updates to storageCache via chrome.storage.onChanged events. Because of the single-event-loop nature of JS, this means the cache will only be updated while your code doesn't run, but in many cases that's acceptable.
Similarly, if you want to propagate changes to storageCache to the real storage, just setting storageCache['key'] is not enough. You would need to write a set(key, value) shim that BOTH writes to storageCache and schedules an (asynchronous) chrome.storage.sync.set.
Implementing those is left as an exercise.

Make the main function "async" and make a "Promise" in it :)
async function mainFuction() {
var p = new Promise(function(resolve, reject){
chrome.storage.sync.get({"disableautoplay": true}, function(options){
resolve(options.disableautoplay);
})
});
const configOut = await p;
console.log(configOut);
}

Yes, you can achieve that using promise:
let getFromStorage = keys => new Promise((resolve, reject) =>
chrome.storage.sync.get(...keys, result => resolve(result)));

chrome.storage.sync.get has no returned values, which explains why you would get undefined when calling something like
var a = chrome.storage.sync.get({"disableautoplay": true});
chrome.storage.sync.get is also an asynchronous method, which explains why in the following code a would be undefined unless you access it inside the callback function.
var a;
window.onload = function(){
chrome.storage.sync.get({"disableautoplay": true}, function(e){
// #2
a = e.disableautoplay; // true or false
});
// #1
a; // undefined
}

If you could manage to work this out you will have made a source of strange bugs. Messages are executed asynchronously which means that when you send a message the rest of your code can execute before the asychronous function returns. There is not guarantee for that since chrome is multi-threaded and the get function may delay, i.e. hdd is busy.
Using your code as an example:
var a;
window.onload = function(){
chrome.storage.sync.get({"disableautoplay": true}, function(e){
a = e.disableautoplay;
});
}
if(a)
console.log("true!");
else
console.log("false! Maybe undefined as well. Strange if you know that a is true, right?");
So it will be better if you use something like this:
chrome.storage.sync.get({"disableautoplay": true}, function(e){
a = e.disableautoplay;
if(a)
console.log("true!");
else
console.log("false! But maybe undefined as well");
});
If you really want to return this value then use the javascript storage API. This stores only string values so you have to cast the value before storing and after getting it.
//Setting the value
localStorage.setItem('disableautoplay', JSON.stringify(true));
//Getting the value
var a = JSON.stringify(localStorage.getItem('disableautoplay'));

var a = await chrome.storage.sync.get({"disableautoplay": true});
This should be in an async function. e.g. if you need to run it at top level, wrap it:
(async () => {
var a = await chrome.storage.sync.get({"disableautoplay": true});
})();

How to pass data around from an asynchronous function in NodeJS, using unconventional methods?

I've been playing with jsdom, which is a module for node.js. This following code on the bottom is from their documentation page. My problem is how to return something from asynchronous functions.
I know that this is a question that is asked a lot, probably by me as well. I also know that callbacks are a good friend when it comes to these kind of problems. My goal here is to find a workaround which might act like a cookie or a Session variable in PHP, in order to transfer that little bit of data to the outer scope, outside the asynchronous function. Then it should be accessible once the data is set from the outer scope.
First thing I want to know is:
Is there already a way to store data somewhere like a cookie or session that exists in the outer scope and accessible once I've done what I had to do?
If I was to write the data to a file, in point B in the code, and read it at point C, wouldn't I have to write a some sort of timeout function to wait for a few seconds before reading the file? My experience in working with Asynchronous functions in nodejs has sometimes shown that I had to wait a few seconds before the writing process was done before trying to read it. Would this be the case here too? If yes, wouldn't it mean it would have to happen if where I saved the data was memory?
If I was to write a c++ plugin for this purpose, that acted as a separate data bay where we could save(data) at point B to the memory and retrieve(data) at point C from the memory; would this work?
Honestly, I do not like writing temporary files to work around the asynchronous functions. I have been looking for a simple yet effective way to pass data around, but I need some guidance from experienced programmers like you to surpass the unnecessary approaches to this problem.
If you could toss around some ideas for me, stating what might work and what might not work, I'd appreciate it.
Here's the example code:
// Print all of the news items on hackernews
var jsdom = require("jsdom");
// var result;
// A) Outer Scope: Since the function is async in done, storing the result here and echoing in point C is pointless.
jsdom.env({
html: "http://news.ycombinator.com/",
scripts: ["http://code.jquery.com/jquery.js"],
done: function (errors, window) {
var $ = window.$;
console.log("HN Links");
$("td.title:not(:last) a").each(function() {
console.log(" -", $(this).text());
});
// B) let's say I want to return something I've scavenged here.
// result = $("a");
}
});
// C)
// console.log(result)

You need to clear your head of your synchronous experience that thinks code lower in the file happens later in time. It does not necessarily do that in node, ever. Here's the deal. In node, you place orders like at a restaurant, and you don't do it like:
1. Order a salad
2. Wait 11 minutes
3. Eat the salad
You do it like this
1. Order a salad
2. Wait for the server to serve you the salad
3. Eat the salad
The first example is a race condition and a terrible bug in your program that will cause either the salad waiting around to be eaten for no reason or trying to eat a salad that isn't there yet.
Don't think "I want to return something here", think "this data is ready". So you can have:
function eatSalad() {...}
placeOrder("salad", eatSalad);
Where eatSalad is the callback for the placeOrder routine, which does the necessary I/O to get the salad. Notice how even though eatSalad is earlier in the file, it happens later chronologically. You don't return things, you invoke callbacks with data you have prepared.
Here's your snippet made asynchronous.
// Print all of the news items on hackernews
var jsdom = require("jsdom");
// var result;
// A) Outer Scope: Since the function is async in done, storing the result here and echoing in point C is pointless.
jsdom.env({
html: "http://news.ycombinator.com/",
scripts: ["http://code.jquery.com/jquery.js"],
done: function (errors, window) {
var $ = window.$;
console.log("HN Links");
$("td.title:not(:last) a").each(function() {
console.log(" -", $(this).text());
});
// B) let's say I want to return something I've scavenged here.
// result = $("a");
resultIsReady($("a"));
}
});
function resultIsReady(element) {
console.log(element);
}
EDIT TO ADD to answer your question from the comments, node code will generally be built up not from functions that return things, but from functions that invoke callback functions with their "return value". The return keyword is only used to actually return a value for in-memory code that does not do any I/O. So finding the mean of an in-memory array can just return it, but finding the mean from a database result set must invoke a callback function. The basic paradigm is built up your programs from functions like this (pseudocode DB library):
function getUser(email, callback) {
db.users.where({email: email}, function (error, user) {
if (error) {
//This return statement is just for early termination
//of the function. The value returned is discarded
return callback(error);
}
callback(null, user);
});;
}
So that's how you do things. And typically functions like this do a very limited number of IO calls (1 or 2 are common, then you start falling into nesting hell and need to refactor).
I personally write lots of functions like that and then use the async library to describe the higher-order sequence of things that needs to happen. There are lots of other popular flow control libraries as well, and some people like the promises pattern. However, at the moment some of the core node community members seem to be advocating callbacks as the one true way and promises seem to be falling out of favor.

Avoid using synchronous code in any place where there is a chance for blocking the execution, such as database operations, file IO, network data retrieval, long calculations etc.
In your example use callback when you finish your computation to continue with execution, you could also take a look at async https://npmjs.org/package/async library which is de facto standard for hairier calls :
function sendData(result) {
res.json(result);
}
var jsdom = require("jsdom");
// var result;
// A) Outer Scope: Since the function is async in done, storing the result here
// and echoing in point C is pointless.
jsdom.env({
html: "http://news.ycombinator.com/",
scripts: ["http://code.jquery.com/jquery.js"],
done: function (errors, window) {
var $ = window.$;
console.log("HN Links");
$("td.title:not(:last) a").each(function () {
console.log(" -", $(this).text());
});
// B) let's say I want to return something I've scavenged here.
var result = $("a");
sendData(result);
}
});

Ignoring old multiple asynchronous ajax requests

I've got a custom javascript autocomplete script that hits the server with multiple asynchronous ajax requests. (Everytime a key gets pressed.)
I've noticed that sometimes an earlier ajax request will be returned after a later requests, which messes things up.
The way I handle this now is I have a counter that increments for each ajax request. Requests that come back with a lower count get ignored.
I'm wondering: Is this proper? Or is there a better way of dealing with this issue?
Thanks in advance,
Travis

You can store a "global" currentAjaxRequest, which holds the structure of the last XHR request. Then you can abort the current request when you make a new one.
For example:
var currentAjaxRequest = null;
function autoCompleteStuff() {
if(currentAjaxRequest !== null) {
currentAjaxRequest.abort();
}
currentAjaxRequest = $.get(..., function(...) {
currentAjaxRequest = null;
...
});
}
To avoid naming conflicts, wrap that in an anonymous, instantly-executed function, if needed.

Pattern for wrapping an Asynchronous JavaScript function to make it synchronous

I'm working with a JavaScript API where most of the functions are asynchronous. The API is the WebKit JavaScript Database API which is a binding to a subset of functionality to manipulate SQLite3 databases. I understand the design decision to make things async as to not block and provide a responsive user interface. In my situation I know that my usage of the async API calls will execute fast. Since this is the case I'd like to provide my developers a cleaner and easier to use wrapper API that forces synchronous calls.
Here's the async call
db.executeSql(sqlStatement, function(result) {
// do something with result
});
And here's what I'd like to be able to do
var result = dbWrapper.executeSql(sqlStatement);
// do something with result
Is there a design pattern/way to do this? A written or linked to code example is preferred. The target platform/broswer is Mobile Safari on the iPhone.
Thank you

Sorry, JavaScript does not provide the language primitives (eg. threads or coroutines) to make asynchronous things act synchronously or vice-versa.
You generally* get one thread of execution only, so you can't get a callback from a timer or XMLHttpRequest readystatechange until the stack of calls leading to the creation of the request has completely unravelled.
So in short, you can't really do it; the approach with nested closures on the WebKit page you linked is the only way I know of to make the code readable in this situation.
*: except in some obscure situations which wouldn't help you and are generally considered bugs

StratifiedJS allows you to do exactly that.
There's even an article on how to apply it on browser storage:
http://onilabs.com/blog/stratifying-asynchronous-storage
And this is the Stratified JavaScript library it uses https://gist.github.com/613526
The example goes like:
var db = require("webdatabase").openDatabase("CandyDB", ...);
try {
var kids = db.executeSql("SELECT * FROM kids").rows;
db.executeSql("INSERT INTO kids (name) VALUES (:name);", [kids[0]]);
alert("done");
} catch(e) {
alert("something went wrong");
}
maybe a bit late, but the tech didn't exist back then ;)

You can try something like:
function synch()
{
var done = false;
var returnVal = undefined;
// asynch takes a callback method
// that is called when done
asynch(function(data) {
returnVal = data;
done = true;
});
while (done == false) {};
return returnVal;
}
But that may freeze your browser for the duration of the asynch method...
Or take a look at Narrative JavaScript: Narrative JavaScript is a small extension to the JavaScript language that enables blocking capabilities for asynchronous event callbacks. This makes asynchronous code refreshingly readable and comprehensible.
http://neilmix.com/narrativejs/doc/index.html
Mike

if you are using jQuery Ajax :
$.ajax()
you can set the attribute of asynch to false ,
and then you will have a synch ajax request to the server.

We are using GWT RPC which also has an async API. The solution that we are currently using to make several async calls in serial is call chaining:
callA(function(resultA) {
callB(resultA, function(resultB) {
callC(); //etc.
});
});
This nested approach achieves what you want but it is verbose and hard to read for newcomers. One of the approaches that we have investigated is adding the calls that we need to make to a stack and executing them in order:
callStack = [
callA(),
callB(),
callC()
];
callStack.execute();
Then the callstack would manage:
Invoking the calls in serial (i.e. the wiring in the first example)
Passing the result from one call forward to the next.
However, because Java doesn't have function references, each call on the call stack would require an anonymous class so we stopped short of such a solution. However, you may have more success in javascript.
Good luck!

This doesn't actually implement synchronous operation of the db query, but this was my solution for easy management. Basically use the calling function as the callback function, and test for the results argument. If the function receives results, it parses them, if not, it sends itself as a callback to the query method.
render: function(queryResults){
if (typeof queryResults != 'undefined'){
console.log('Query completed!');
//do what you will with the results (check for query errors here)
} else {
console.log('Beginning query...');
this.db.read(this.render); //db.read is my wrapper method for the sql db, and I'm sending this render method as the callback.
}
}

I am not sure if this is the right place but I cam here searching for answers to making an synchronous calls in Firefox. the solution would be to remove onreadystatechange callback and do a direct call.
This is what I had found and my solution
synchronous call back with rest service