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JavaScript function blocks web socket & causes sync issue & delay

I have a web socket that receives data from a web socket server every 100 to 200ms, ( I have tried both with a shared web worker as well as all in the main.js file),
When new JSON data arrives my main.js runs filter_json_run_all(json_data) which updates Tabulator.js & Dygraph.js Tables & Graphs with some custom color coding based on if values are increasing or decreasing
1) web socket json data ( every 100ms or less) -> 2) run function filter_json_run_all(json_data) (takes 150 to 200ms) -> 3) repeat 1 & 2 forever
Quickly the timestamp of the incoming json data gets delayed versus the actual time (json_time 15:30:12 vs actual time: 15:31:30) since the filter_json_run_all is causing a backlog in operations.
So it causes users on different PC's to have websocket sync issues, based on when they opened or refreshed the website.
This is only caused by the long filter_json_run_all() function, otherwise if all I did was console.log(json_data) they would be perfectly in sync.
Please I would be very very grateful if anyone has any ideas how I can prevent this sort of blocking / backlog of incoming JSON websocket data caused by a slow running javascript
function :)
I tried using a shared web worker which works but it doesn't get around the delay in main.js blocked by filter_json_run_all(), I dont thing I can put filter_json_run_all() since all the graph & table objects are defined in main & also I have callbacks for when I click on a table to update a value manually (Bi directional web socket)
If you have any ideas or tips at all I will be very grateful :)
worker.js:
const connectedPorts = [];
// Create socket instance.
var socket = new WebSocket(
'ws://'
+ 'ip:port'
+ '/ws/'
);
// Send initial package on open.
socket.addEventListener('open', () => {
const package = JSON.stringify({
"time": 123456,
"channel": "futures.tickers",
"event": "subscribe",
"payload": ["BTC_USD", "ETH_USD"]
});
socket.send(package);
});
// Send data from socket to all open tabs.
socket.addEventListener('message', ({ data }) => {
const package = JSON.parse(data);
connectedPorts.forEach(port => port.postMessage(package));
});
/**
* When a new thread is connected to the shared worker,
* start listening for messages from the new thread.
*/
self.addEventListener('connect', ({ ports }) => {
const port = ports[0];
// Add this new port to the list of connected ports.
connectedPorts.push(port);
/**
* Receive data from main thread and determine which
* actions it should take based on the received data.
*/
port.addEventListener('message', ({ data }) => {
const { action, value } = data;
// Send message to socket.
if (action === 'send') {
socket.send(JSON.stringify(value));
// Remove port from connected ports list.
} else if (action === 'unload') {
const index = connectedPorts.indexOf(port);
connectedPorts.splice(index, 1);
}
});
Main.js This is only part of filter_json_run_all which continues on for about 6 or 7 Tabulator & Dygraph objects. I wante to give an idea of some of the operations called with SetTimeout() etc
function filter_json_run_all(json_str){
const startTime = performance.now();
const data_in_array = json_str //JSON.parse(json_str.data);
// if ('DATETIME' in data_in_array){
// var milliseconds = (new Date()).getTime() - Date.parse(data_in_array['DATETIME']);
// console.log("milliseconds: " + milliseconds);
// }
if (summary in data_in_array){
if("DATETIME" in data_in_array){
var time_str = data_in_array["DATETIME"];
element_time.innerHTML = time_str;
}
// summary Data
const summary_array = data_in_array[summary];
var old_sum_arr_krw = [];
var old_sum_arr_irn = [];
var old_sum_arr_ntn = [];
var old_sum_arr_ccn = [];
var old_sum_arr_ihn = [];
var old_sum_arr_ppn = [];
var filtered_array_krw_summary = filterByProperty_summary(summary_array, "KWN")
old_sum_arr_krw.unshift(Table_summary_krw.getData());
Table_summary_krw.replaceData(filtered_array_krw_summary);
//Colour table
color_table(filtered_array_krw_summary, old_sum_arr_krw, Table_summary_krw);
var filtered_array_irn_summary = filterByProperty_summary(summary_array, "IRN")
old_sum_arr_irn.unshift(Table_summary_inr.getData());
Table_summary_inr.replaceData(filtered_array_irn_summary);
//Colour table
color_table(filtered_array_irn_summary, old_sum_arr_irn, Table_summary_inr);
var filtered_array_ntn_summary = filterByProperty_summary(summary_array, "NTN")
old_sum_arr_ntn.unshift(Table_summary_twd.getData());
Table_summary_twd.replaceData(filtered_array_ntn_summary);
//Colour table
color_table(filtered_array_ntn_summary, old_sum_arr_ntn, Table_summary_twd);
// remove formatting on fwds curves
setTimeout(() => {g_fwd_curve_krw.updateOptions({
'file': dataFwdKRW,
'labels': ['Time', 'Bid', 'Ask'],
strokeWidth: 1,
}); }, 200);
setTimeout(() => {g_fwd_curve_inr.updateOptions({
'file': dataFwdINR,
'labels': ['Time', 'Bid', 'Ask'],
strokeWidth: 1,
}); }, 200);
// remove_colors //([askTable_krw, askTable_inr, askTable_twd, askTable_cny, askTable_idr, askTable_php])
setTimeout(() => { askTable_krw.getRows().forEach(function (item, index) {
row = item.getCells();
row.forEach(function (value_tmp){value_tmp.getElement().style.backgroundColor = '';}
)}); }, 200);
setTimeout(() => { askTable_inr.getRows().forEach(function (item, index) {
row = item.getCells();
row.forEach(function (value_tmp){value_tmp.getElement().style.backgroundColor = '';}
)}); }, 200);
color_table Function
function color_table(new_arr, old_array, table_obj){
// If length is not equal
if(new_arr.length!=old_array[0].length)
console.log("Diff length");
else
{
// Comparing each element of array
for(var i=0;i<new_arr.length;i++)
//iterate old dict dict
for (const [key, value] of Object.entries(old_array[0][i])) {
if(value == new_arr[i][key])
{}
else{
// console.log("Different element");
if(key!="TENOR")
// console.log(table_obj)
table_obj.getRows()[i].getCell(key).getElement().style.backgroundColor = 'yellow';
if(key!="TIME")
if(value < new_arr[i][key])
//green going up
//text_to_speech(new_arr[i]['CCY'] + ' ' +new_arr[i]['TENOR']+ ' getting bid')
table_obj.getRows()[i].getCell(key).getElement().style.backgroundColor = 'Chartreuse';
if(key!="TIME")
if(value > new_arr[i][key])
//red going down
table_obj.getRows()[i].getCell(key).getElement().style.backgroundColor = 'Crimson';
}
}
}
}
Potential fudge / solution, thanks Aaron :):
function limiter(fn, wait){
let isCalled = false,
calls = [];
let caller = function(){
if (calls.length && !isCalled){
isCalled = true;
if (calls.length >2){
calls.splice(0,calls.length-1)
//remove zero' upto n-1 function calls from array/ queue
}
calls.shift().call();
setTimeout(function(){
isCalled = false;
caller();
}, wait);
}
};
return function(){
calls.push(fn.bind(this, ...arguments));
// let args = Array.prototype.slice.call(arguments);
// calls.push(fn.bind.apply(fn, [this].concat(args)));
caller();
};
}
This is then defined as a constant for a web worker to call:
const filter_json_run_allLimited = limiter(data => { filter_json_run_all(data); }, 300); // 300ms for examples
Web worker calls the limited function when new web socket data arrives:
// Event to listen for incoming data from the worker and update the DOM.
webSocketWorker.port.addEventListener('message', ({ data }) => {
// Limited function
filter_json_run_allLimited(data);
});
Please if anyone knows how websites like tradingview or real time high performance data streaming sites allow for low latency visualisation updates, please may you comment, reply below :)

I'm reticent to take a stab at answering this for real without knowing what's going on in color_table. My hunch, based on the behavior you're describing is that filter_json_run_all is being forced to wait on a congested DOM manipulation/render pipeline as HTML is being updated to achieve the color-coding for your updated table elements.
I see you're already taking some measures to prevent some of these DOM manipulations from blocking this function's execution (via setTimeout). If color_table isn't already employing a similar strategy, that'd be the first thing I'd focus on refactoring to unclog things here.
It might also be worth throwing these DOM updates for processed events into a simple queue, so that if slow browser behavior creates a rendering backlog, the function actually responsible for invoking pending DOM manipulations can elect to skip outdated render operations to keep the UI acceptably snappy.
Edit: a basic queueing system might involve the following components:
The queue, itself (this can be a simple array, it just needs to be accessible to both of the components below).
A queue appender, which runs during filter_json_run_all, simply adding objects to the end of the queue representing each DOM manipulation job you plan to complete using color_table or one of your setTimeout` callbacks. These objects should contain the operation to performed (i.e: the function definition, uninvoked), and the parameters for that operation (i.e: the arguments you're passing into each function).
A queue runner, which runs on its own interval, and invokes pending DOM manipulation tasks from the front of the queue, removing them as it goes. Since this operation has access to all of the objects in the queue, it can also take steps to optimize/combine similar operations to minimize the amount of repainting it's asking the browser to do before subsequent code can be executed. For example, if you've got several color_table operations that coloring the same cell multiple times, you can simply perform this operation once with the data from the last color_table item in the queue involving that cell. Additionally, you can further optimize your interaction with the DOM by invoking the aggregated DOM manipulation operations, themselves, inside a requestAnimationFrame callback, which will ensure that scheduled reflows/repaints happen only when the browser is ready, and is preferable from a performance perspective to DOM manipulation queueing via setTimeout/setInterval.

Track user time in completing a particular action in a website

I want to track how much time user is taking in completing a particular action (including server response time and render time(DOM related changes )) in website.
I have tried it in Angular framework. To do it, I am thinking of recording the time when user started the action and I want to note the time when the action is completed. As a developer, I will know when user started the activity and when user finish the action like search, filter, edit, add, delete etc. So, we can take the difference b/w them. But to note every action, we have to write code in every part of the app. Can we create a plugin so that we can use it everywhere instead of writing same code everywhere to track the time of user. Any approach to create it? Or is there any tool available to achieve this feature?

Would something like this help?
#Injectable({provideIn: 'root'})
export class TrackingService {
private cache: {[id: number]: {description: string, time: number}} = {};
private id: number = 0;
public startTracking(actionDescription: string): number{
const id = ++this.id;
this.cache[id] = { description: actionDescription, time: new Date().getTime() };
return id;
}
public stopTracking(actionId: number){
const data = this.cache[actionId];
if(data){
const elapsed = new Date().getTime() - data.time;
// ...
// Do something with your 'elapsed' and 'data.description'
// ...
delete this.cache[id];
return {...data, elapsed: elapsed};
}
throw `No action with id [${actionId}] running! `;
}
}
Ad then anywhere you need to track an action:
private actionId: number;
constructor(private trackingService: TrackingService){}
startAction(){
this.actionId = this.trackingService.startTracking('Description');
}
stopAction(){
const trackingResult = this.trackingService.stopTracking(this.actionId);
}
You can automate the tracking in some places, for example for routing:
// app.module.ts
private routeChangeSubscription: Subscription;
private configLoadActionId: number;
private navigationActionId: number;
constructor(private router: Router, private trackingService: TrackingService){
this.routeChangeSubscription = router.events.subscribe((event: Event) => {
if (event instanceof RouteConfigLoadStart) {
this.configLoadActionId = this.trackingService.startTracking('configLoad');
}
else if (event instanceof RouteConfigLoadEnd) {
const result = this.trackingService.stopTracking(this.configLoadActionId);
// ... process the result if you wish
}
else if (event instanceof NavigationStart) {
this.navigationActionId = this.trackingService.startTracking('navigation');
}
else if (event instanceof NavigationEnd) {
const result = this.trackingService.stopTracking(this.navigationActionId);
// ... process the result if you wish
}
});
}
Or for HTTP requests:
// http-tracking.interceptor
export class HttpTrackingInterceptor implements HttpInterceptor {
constructor(private trackingService: TrackingService) {}
intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
const actionId = this.trackingService.startTracking('HTTP request');
return next.handle(req.clone()).pipe(
tap(r => this.trackingService.stopTracking(actionId))
);
}
}
// app.module.ts
#NgModule({
// ... other module stuff
providers: [
// ... other providers
{
provide: HTTP_INTERCEPTORS,
useClass: HttpTrackingInterceptor,
multi: true,
deps: [TrackingService]
}
]
})
export class AppModule { ... }
You can easily extend the TrackingService to return Promises or Observables or whatever else, in case you prefer that...
Hope this helps a little :-)

Can we create a plugin so that we can use it everywhere instead of
writing same code everywhere to track the time of user. Any approach
to create it? Or is there any tool available to achieve this feature?
It's a very important Feature Request by many. So, I write a detailed, working and simple solution on the subject here.
#himanshu-garg You are requesting a feature already created for this workflow. It's a plugin you can include in any website. It's none other than activity tracking in timeonsite.js
Look at the following code,
<head>
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/timeonsite/1.2.0/timeonsitetracker.js"></script>
<script>
var config = {
// track page by seconds. Default tracking is by milliseconds
trackBy: 'seconds',
callback: function(data) { /* callback denotes your data tracking is real-time */
console.log(data);
var endPointUrl = 'http://example.com' //Replace with your actual backend API URL http://localhost/tos
if (data && data.trackingType) {
if (data.trackingType == 'tos') {
if (Tos.verifyData(data) != 'valid') {
console.log('Data abolished!');
return;
}
}
// make use of sendBeacon if this API is supported by your browser.
if (navigator && typeof navigator.sendBeacon === 'function') {
data.trasferredWith = 'sendBeacon';
var blob = new Blob([JSON.stringify(data)], {type : 'application/json'});
navigator.sendBeacon(endPointUrl, blob);
}
}
}
};
var Tos;
if (TimeOnSiteTracker) {
Tos = new TimeOnSiteTracker(config);
}
</script>
</head>
Then, when the user clicks on a specific action in the site, for example "edit the post" or "click on the create post",
You just initiate the Tos.startActivity() API like,
Tos.startActivity({actionPerfomed: 'Edit a post'});
Then when the user completes the edit or create post actions and when he finally clicks the "save/submit" button, you trigger the Tos.endActivity() API like,
Tos.endActivity({customData: 'custom data if any here...'});
You'll see following object directly saved into your table,
{
TOSId: 585872449448,
TOSSessionKey: "14802525481391382263",
TOSUserId: "anonymous",
title: "Test application - TimeOnSiteTracker",
URL: "http://example.com/post/nature-is-beautiful/edit.php",
activityStart: "2021-11-27 13:20:46.707",
activityEnd: "2021-11-27 13:20:50.213",
timeTaken:4,
timeTakenByDuration: "0d 00h 00m 04s"
timeTakenTrackedBy: "second",
trackingType: "activity",
actionPerfomed: "Edit a post", //optional fields
customData: "custom data if any here..." //optional fields
}
As you can see, the actions
"Edit/Create post" is captured
"timeTaken" is captured in seconds/milliseconds depending upon configuration
"type:activity" is captured
"activityStart" is captured
"activityEnd" is captured
"TOSUserId" // who does the action along with TOSSessionKey to uniquely identify the session.
What else you need? Since it's stored in SQL DB table, you can do analysis/reporting queries yourself and take it to top-level management for decisions. The same is the case for NoSQL as well. Timeonsite.js is supporting both RDBMS and NoSql DB types.
On top of it, 1.Minimize tab, 2.Inactive tab and 3.Switch tab's idle time are all computed and ignored automatically by the tracker itself.
This tracker can be plugged-in in any library Angular, React, Jquery etc. since it's plain vanilla JS library.
Let me know if you need more input on the subject. I can assist you on this.

You have to write a simple Event Tracker in your client code. Since I don't know which events you want to track, I'll provide the solution for a general case.
Also, you'll have to manually trigger the start and stop tracking.
EventTracker = {
trackedEvents: {},
start: function(key) {
var startTime = new Date();
this.trackedEvents[key] = {
start: startTime
}
},
stop: function(key) {
var endTime = new Date();
this.trackedEvents[key]['duration'] = (endTime - this.trackedEvents[key]['start']) / 1000 + 's';
this.trackedEvents[key]['end'] = endTime;
},
}
// Use EventTracker everywhere to track performance
// Example:
EventTracker.start('search_track'); // User searches, start tracking.
setTimeout(function() {
EventTracker.stop('search_track'); // Records fetched after 5 seconds. Stop tracking.
console.log(EventTracker.trackedEvents);
}, 5000);
You can track all events according to your need. For server response, use: EventTracker.start('search_ajax_track') when you make the request and stop the tracking when you get the response.
You can modify above code to measure other parameters according to your requirements.

I am going to recommend you use custom Google Analytics events. In particular User Timings. This allows you to log specific timings on your webpage, you can log with your own labels and categories.
To quote the documentation:
User timings allow developers to measure periods of time using the
analytics.js library. This is particularly useful for developers to
measure the latency, or time spent, making AJAX requests and loading
web resources.
I have some sample code below, this just hooks into clicks, and will get a descriptor from attribute data-name - if not available will just log as 'Anonymous Click' - you can customise this to not track unmarked items. You can also hook into ajax calls and other notable events, without knowing your specific requirements it's hard to give further examples.
Example markup helper to lock click events.
<button data-name="Foo"/>
The below code does the logging, note that it logs using window.performance.now() - which will return the time from when the page was loaded in milliseconds. This will allow you to generate a timeline of user interactions as opposed to getting raw time spent on a single task, which by the way Google Analytics reports can calculate for you.
(function($, Analytics) {
init_hooks();
function init_hooks() {
$('body').on('click', track);
}
function track(e) {
// Get a name to record this against
var name = e.target.data(name) || "Anonymous Click";
// Time since page loaded
var time = window.performance.now()
Analytics('send', {
hitType: 'timing',
timingCategory: 'Front End Intereactions',
timingVar: name,
timingValue: time
});
}
})(jQuery, ga)
Find out more look at the docs.

You could instrument your code with OpenTracing for Js.
You will need to add a request in your transaction start and end.
Also a OpenTracing server to receive request from the browser.

GetScriptLock does not seem to work

I am trying to generate a unique number when a form is submitted. I have simplified my script to the following for testing.
function onFormSubmit(event) {
// Get a script lock, because we're about to modify a shared resource.
var lock = LockService.getScriptLock();
// Wait for up to 30 seconds for other processes to finish.
lock.waitLock(30000);
var ticketNumber = Number(ScriptProperties.getProperty('lastTicketNumber')) + 1;
ScriptProperties.setProperty('lastTicketNumber', ticketNumber);
targetCell = event.range.offset(0, event.range.getNumColumns(), 1, 1);
targetCell.setValue(ticketNumber);
SpreadsheetApp.flush();
// Release the lock so that other processes can continue.
lock.releaseLock();
};
I find that if I submit two forms within a second of each other I get the same ticketnumber.
Any help would be appreciated.

Preface: You are using the deprecated ScriptProperties service, this has been replaced by the Properties Service. You probably want to change this first.
In the past I have received the same results when trying to utilize the project properties in rapid succession. It's almost as if the old value hangs around in whatever caching apps script uses for script properties for a few seconds.
I would recommend utilizing the Cache Service to suppliment for scripts that need to reflect changes immediately.
Modified Code:
function onFormSubmit(event) {
// Get a script lock, because we're about to modify a shared resource.
var lock = LockService.getScriptLock();
// Wait for up to 30 seconds for other processes to finish.
lock.waitLock(30000);
var scriptCache = CacheService.getScriptCache();
var scriptProperties = PropertiesService.getScriptProperties();
var cachedTicketNumber = scriptCache.get('lastTicketNumber');
var ticketNumber;
if(cachedTicketNumber !== null){
ticketNumber = Number(cachedTicketNumber) + 1;
} else {
//Cache has expired/does not exist, fall back to properties service
ticketNumber = Number(scriptProperties.getProperty('lastTicketNumber')) + 1;
}
//Set properties service, and cache values of the ticket number
scriptProperties.setProperty('lastTicketNumber', ticketNumber);
scriptCache.put('lastTicketNumber', ticketNumber, 21600); //21600 seconds = 6 hours, if you want it to last that long
targetCell = event.range.offset(0, event.range.getNumColumns(), 1, 1);
targetCell.setValue(ticketNumber);
SpreadsheetApp.flush();
// Release the lock so that other processes can continue.
lock.releaseLock();
};

Windows 8 Javascript app activation/launch deferral

So currently in a windows 8 WinJS app I'm coding, I am trying to get the loading of an xml file to take place in the app startup sequence, while the splash screen is still showing, as this xmldoc element is needed for when the home page loads, and loading of the home page will fail without it.
This is my initiation sequence in default.js:
(function () {
"use strict";
var activation = Windows.ApplicationModel.Activation;
var app = WinJS.Application;
var nav = WinJS.Navigation;
var sched = WinJS.Utilities.Scheduler;
var ui = WinJS.UI;
app.addEventListener("activated", function (args) {
if (args.detail.kind === activation.ActivationKind.launch) {
if (args.detail.previousExecutionState !== activation.ApplicationExecutionState.terminated) {
// TODO: This application has been newly launched. Initialize
// your application here.
console.log("Newly Launched!");
var localSettings = Windows.Storage.ApplicationData.current.localSettings;
WinJS.Namespace.define("MyGlobals", { localSettings: localSettings });
// APP RUN TYPE CHECK AND SEQUENCE (FIRST RUN / NOT FIRST RUN):
if (MyGlobals.localSettings.values['firstRunCompleted']) {
console.log("NOT FIRST RUN!");
// CACHE VERSION CHECK. IF APP HAS BEEN UPDATED, INITIATE NEWLY ADDED CACHE VALUES HERE:
} else {
console.log("FIRST RUN!")
MyGlobals.localSettings.values['firstRunCompleted'] = true;
};
//loadXML(); have tried many things with this. doesn't work.
} else {
// TODO: This application has been reactivated from suspension.
// Restore application state here.
var currentVolume = app.sessionState.currentVolume;
if (currentVolume) {
console.log("RESTORE FROM SUSPENSION");
console.log(currentVolume);
};
}
nav.history = app.sessionState.history || {};
nav.history.current.initialPlaceholder = true;
// Optimize the load of the application and while the splash screen is shown, execute high priority scheduled work.
ui.disableAnimations();
var p = ui.processAll().then(function () {
return nav.navigate(nav.location || Application.navigator.home, nav.state);
}).then(function () {
return sched.requestDrain(sched.Priority.aboveNormal + 1);
}).then(function () {
ui.enableAnimations();
});
args.setPromise(p);
args.setPromise(WinJS.UI.processAll().then(function completed() {
loadSavedColour();
// Populate Settings pane and tie commands to Settings flyouts.
WinJS.Application.onsettings = function (e) {
e.detail.applicationcommands = {
"helpDiv": { href: "html/Help.html", title: WinJS.Resources.getString("settings_help").value },
"aboutDiv": { href: "html/About.html", title: WinJS.Resources.getString("settings_about").value },
"settingsDiv": { href: "html/Settings.html", title: WinJS.Resources.getString("settings_settings").value },
};
WinJS.UI.SettingsFlyout.populateSettings(e);
}
As you can see where I have the commented line of "loadXML()", that is where I need the loadXML() function to take place.
Here is my loadXML() function:
function loadXML() {
Windows.ApplicationModel.Package.current.installedLocation.getFolderAsync("foldername").then(function (externalDtdFolder) {
externalDtdFolder.getFileAsync(MyGlobals.localSettings.values['currentBook']).done(function (file) {
Windows.Data.Xml.Dom.XmlDocument.loadFromFileAsync(file).then(function (doc) {
WinJS.Namespace.define("MyGlobals", {
xmlDoc: doc,
});
})
})
});
};
(loadXML is a working function and works in other scenarios)
However, the issue is that before the loadXML function finishes, the app splash screen goes away, and the next home.html home page loads, which starts the accompanying home.js, which has a function that requires the MyGlobals.xmlDoc object that loadXML should have made. This immediately crashes the app, as MyGlobals.xmlDoc is undefined/null.
I used to have this app working by running loadXML in home.js for the home.html page directly, but in that scenario the XML document is reloaded every time navigation is made to the page, wasting time and resources. As such, I'm trying to move the xmldocument loading into the app startup/initialization.
Thanks a lot!

loadXML has async functionality and you need to handle that.
You shouldn't expect that the loadFromFileAsync (or any of the other async functions) have completed before it returns to the caller. If your code doesn't wait, you'll find that the MyGlobals.xmlDoc value won't be set when you need it.
I've renamed it below to be more accurate as to its behavior. The big change is that it returns a Promise that can be used by the caller to properly wait for the Xml doc to be loaded. This Promise could be used with other Promises to wait on multiple conditions if you'd like (or in the case, other async work).
function loadXMLAsync() {
return new WinJS.Promise(function (complete, error, progress) {
var localSettings = MyGlobals.localSettings.values;
var installedLocation = Windows.ApplicationModel.Package.current.installedLocation;
installedLocation.getFolderAsync("foldername").then(function (externalDtdFolder) {
externalDtdFolder.getFileAsync(values['currentBook']).done(function (file) {
Windows.Data.Xml.Dom.XmlDocument.loadFromFileAsync(file).then(function (doc) {
complete(doc);
});
});
});
});
};
Then, in use:
loadXmlAsync().then(function(doc) {
WinJS.Namespace.define("MyGlobals", {
xmlDoc: doc,
});
// and any other code that should wait until this has completed
});
The code above does not handle errors.

I believe what you need to do is to extend the splash screen to give your app more time to initialize UI. For your scenario, it's loading the xml.
I will suggest you read How to extend the splash screen (HTML). The main idea is to display an extended splash screen(you can use the same image as the default one) in the activated event, then call your loadXML.

In addition to other comments, what you really need to do is include the promise from loadXml with what you pass to args.setPromise. As you know, setPromise is a way to tell the app loader to wait until that promise is fulfilled before removing the splash screen. However, in your code you're calling setPromise multiple times. What you should be doing is joining all the promises you care about (animations, loadXml, and setting loading) with WinJS.Promise.join, so that you get a single promise that's then waiting on all the other three, and when that one is fulfilled, then remove the splash screen.
Alan's suggestion for an extended splash screen is helpful if that whole loading process ends up taking too long, as doing an extended splash gives you total control over what's happening and when the transition happens to your main page.

Javascript memory consumption with map() over a large set and callbacks

I don't even know how to properly ask this question but I have concerns about the performance (mostly memory consumption) of the following code. I am anticipating that this code will consume a lot of memory because of map on a large set and a lot of 'hanging' functions that wait for external service. Are my concerns justified here? What would be a better approach?
var list = fs.readFileSync('./mailinglist.txt') // say 1.000.000 records
.split("\n")
.map( processEntry );
var processEntry = function _processEntry(i){
i = i.split('\t');
getEmailBody( function(emailBody, name){
var msg = {
"message" : emailBody,
"name" : i[0]
}
request(msg, function reqCb(err, result){
...
});
}); // getEmailBody
}
var getEmailBody = function _getEmailBody(obj, cb){
// read email template from file;
// v() returns the correct form for person's name with web-based service
v(obj.name, function(v){
cb(obj, v)
});
}

If you're worried about submitting a million http requests in a very short time span (which you probably should be), you'll have to set up a buffer of some kind.
one simple way to do it:
var lines = fs.readFileSync('./mailinglist.txt').split("\n");
var entryIdx = 0;
var done = false;
var processNextEntry = function () {
if (entryIdx < lines.length) {
processEntry(lines[entryIdx++]);
} else {
done = true;
}
};
var processEntry = function _processEntry(i){
i = i.split('\t');
getEmailBody( function(emailBody, name){
var msg = {
"message" : emailBody,
"name" : name
}
request(msg, function reqCb(err, result){
// ...
!done && processNextEntry();
});
}); // getEmailBody
}
// getEmailBody didn't change
// you set the ball rolling by calling processNextEntry n times,
// where n is a sensible number of http requests to have pending at once.
for (var i=0; i<10; i++) processNextEntry();
Edit: according to this blog post node has an internal queue system, it will only allow 5 simultaneous requests. But you can still use this method to avoid filling up that internal queue with a million items if you're worried about memory consumption.

Firstly I would advise against using readFileSync, and instead favour the async equivalent. Blocking on IO operations should be avoided as reading from a disk is very expensive, and whilst that's the sole purpose of your code now, I would consider how that might change in the future - and arbitrarily wasting clock cycles is never a good idea.
For large data files I would read them in in defined chunks and process them. If you can come up with some schema, either sentinels to distinguish data blocks within the file, or padding to boundaries, then process the file piece by piece.
This is just rough, untested off the top of my head, but something like:
var fs = require("fs");
function doMyCoolWork(startByteIndex, endByteIndex){
fs.open("path to your text file", 'r', function(status, fd) {
var chunkSize = endByteIndex - startByteIndex;
var buffer = new Buffer(chunkSize);
fs.read(fd, buffer, 0, chunkSize, 0, function(err, byteCount) {
var data = buffer.toString('utf-8', 0, byteCount);
// process your data here
if(stillWorkToDo){
//recurse
doMyCoolWork(endByteIndex, endByteIndex + 100);
}
});
});
}
Or look into one of the stream library functions for similar functionality.
H2H
ps. Javascript and Node works extremely well with async and eventing.. using sync is an antipattern in my opinion, and likely to cause code to be a headache in future