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Using Web Workers to run AngularJS functions like $interval?

So I recently decided to make an idle game from AngularJS, but after a few days of coding it I realized a problem.
The $interval function slows down a huge amount when not actively looking at the screen.
Searching on Google and stackoverflow took me to web workers, and one post actually had me figure out how to make a factory of a web worker to implement into my controller, but I was never able to figure out how to make them run functions (or if this is even possible).
myApp.factory("interval", ['$q',
function($q) {
var blobURL = URL.createObjectURL(new Blob([
'function addInterval() {' +
'i = "add()";' +
'postMessage(i);' +
'setTimeout("addInterval()", 10);' +
'}' +
'addInterval();' +
'function saveInterval() {' +
'x = "save()";' +
'postMessage(x);' +
'setTimeout("saveInterval()", 30000);' +
'}' +
'saveInterval();'
], {
type: 'application/javascript'
}));
var worker = new Worker(blobURL);
var defer = $q.defer();
worker.addEventListener('message', function(e) {
defer.resolve(e.data);
}, false);
return {
doWork: function(myData) {
defer = $q.defer();
worker.postMessage(myData); // Send data to our worker.
return defer.promise;
}
};
}
]);
I practically want to know if it's possible to have the web workers run my save() and interval() functions that are in the controller. I tried to console.log(defer.resolve(e.data)), but it returned undefined.
...and I literally have no clue what the deferring/resolving/promising even does.
Thanks!

So after Scott corrected me about how web workers function I decided to set the interval from 10ms to 1000ms...and was defeated...
...but then I got the great idea of "How about instead of making it one fixed rate, I'll cancel the interval upon page/tab blur (not focussed) and change the intervals + divisions accordingly!". This is what I came up with that solved my problems and made the game continue to run - even when not viewing it.
$scope.division = 100;
var x = $interval(add, 10);
angular.element($window).bind('focus', function() {
$scope.division = 100;
$interval.cancel(x);
x = $interval(add, 10);
}).bind('blur', function() {
$scope.division = 1;
$interval.cancel(x);
x = $interval(add, 1000);
});

Fire an event when an NFC card is presented

I am attempting to build a webapp on a Chromebook, I need it to read RFID card serial numbers with an ACR122U NFC. I am using chrome-nfc.
I am reading cards happily, but I do not know how to fire an event when a card is presented.
Are there any events in chrome-nfc I can use to know when a card has been presented to the reader?
EDIT: I have been trying to use chrome.nfc.wait_for_tag, but it does not behave as I would expect.
// With a card on the reader
chrome.nfc.wait_for_tag(device, 10000, function(tag_type, tag_id){
var CSN = new Uint32Array(tag_id)[0];
console.log ( "CSN: " + CSN );
});
[DEBUG] acr122_set_timeout(round up to 1275 secs)
DEBUG: InListPassiveTarget SENS_REQ(ATQA)=0x4, SEL_RES(SAK)=0x8
DEBUG: tag_id: B6CA9B6B
DEBUG: found Mifare Classic 1K (106k type A)
[DEBUG] nfc.wait_for_passive_target: mifare_classic with ID: B6CA9B6B
CSN: 1805372086
// with no card on the reader
chrome.nfc.wait_for_tag(device, 10000, function(tag_type, tag_id){
var CSN = new Uint32Array(tag_id)[0];
console.log ( "CSN: " + CSN );
});
[DEBUG] acr122_set_timeout(round up to 1275 secs)
DEBUG: found 0 target, tg=144
Both return the results as above immediately, it does not seem to matter what number I use for a timeout...
If I call the function with no card on the reader, and then immediately put the card on the reader after function call, I get no output in the console.

I'm not familiar with chrome-nfc, but taking a shot in the dark by reverse engineering the source, it looks like you would want to use the wait_for_tag method, like:
chrome.nfc.wait_for_tag(device, 3000, function(tag_type, tag_id) {
// Do your magic here.
});
...Where device is your reader, 3000 is the maximum time to wait (in ms), and replacing // Do your magic here. with your desired logic. If it times out, both tag_type and tag_id will be null.
If you wanted to wait indefinitely, you could just recursively call a function with the above code. Example:
function waitAllDay(device) {
chrome.nfc.wait_for_tag(device, 1000, function(tag_type, tag_id) {
if(tag_type !== null && tag_id !== null)
{
// Do your magic here.
}
waitAllDay(device);
});
}
That's assuming you want it to continue waiting even after a tag has been presented. Wrap the waitAllDay(device); in an else if you want it to stop once a tag is read.
UPDATE: It seems the wait_for_tag method does not work as intended, so I'm proposing a second solution. I'm leaving the existing solution in place in case the method is fixed by the developers of chrome-nfc.
Another thing to try is to use chrome.nfc.read, passing in a timeout option, inside a window.setInterval.
var timer = window.setInterval(function () {
chrome.nfc.read(device, { timeout: 1000 }, function(type, ndef) {
if(!!type && !!ndef) {
// Do your magic here.
// Uncomment the next line if you want it to stop once found.
// window.clearInterval(timer);
}
});
}, 1000);
Be sure and call window.clearInterval(timer) whenever you want it to stop watching for tags.

While I do not consider this a proper solution; here is a workaround I am using for the time being.
function listen_for_tag(callback, listen_timeout){
var poll_delay = 400; //ms
var listen_loop = null;
if(!listen_timeout){
listen_timeout = 99999999;
}
function check_for_tag(){
if(listen_timeout < 0) {
clearInterval(listen_loop);
console.log("we didnt find a tag. finished");
}
chrome.nfc.wait_for_tag(dev_manager.devs[0].clients[0], 10, function(tag_type, tag_id){
console.log ( "FOUND A TAG!!" );
clearInterval(listen_loop);
// handle the callback (call it now)
var C = callback;
if (C) {
callback = null;
window.setTimeout(function() {
C(tag_type, tag_id);
}, 0);
}
});
listen_timeout -= poll_delay;
}
listen_loop = setInterval(check_for_tag, poll_delay);
}

Run function after another function completes JavaScript and JQuery

I need a little help. I'm trying to run my second function "likeLinks();" but only after my first function "getLikeURLs();" is finished. This is because my 2nd function relies on the links Array to execute. It seems like they are trying to run at the same time.
Any help would be appreciated.
var links = [];
var url = '/' + window.location.pathname.split('/')[1] + '/' + window.location.pathname.split('/')[2] + '/'
getLikeURLs();
likeLinks();
function getLikeURLs() {
for (i = 1; i < parseInt(document.getElementsByClassName('PageNav')[0].getAttribute('data-last')) + 2; i++) {
var link = $.get(url + 'page-' + i, function(data) {
//gets the like links from current page
$(data).find('a[class="LikeLink item control like"]').each(function() {
links.push($(this).attr('href')); // Puts the links in the Array
});
});
}
}
function likeLinks() {
for (t = 0; t <= links.length; t++) {
var token = document.getElementsByName('_xfToken')[0].getAttribute('value')
$.post(links[t], {
_xfToken: token,
_xfNoRedirect: 1,
_xfResponseType: 'json'
}, function(data) {});
}
}

The link variables are actually jQuery deferred objects - store them in an array and then you can use $.when() to create a mew deferred object that only resolves when all of the previous $.get() operations have completed:
function getLikeURLs(url) { // NB: parameter, not global
var defs = [], links = []; // NB: links no longer global
for (...) {
var link = $.get(...);
defs.push(link);
}
// wait for previous `$.get` to finish, and when they have create a new
// deferred object that will return the entire array of links
return $.when.apply($, defs).then(function() { return links; });
}
Then, to start the chain of functions:
getLikeURLs(url).then(likeLinks);
Note that likeLinks will now be passed the array of links instead of accessing it from the global state. That function should also be rewritten to allow you to wait for its $.post calls to complete, too:
function likeLinks(links) {
// loop invariant - take it outside the loop
var token = document.getElementsByName('_xfToken')[0].getAttribute('value');
// create array of deferreds, one for each link
var defs = links.map(function(link) {
return $.post(link, {
_xfToken: token,
_xfNoRedirect: 1,
_xfResponseType: 'json'
});
});
// and another for when they're all done
return $.when.apply($, defs);
}
p.s. don't put that (relatively) expensive parseInt(document.getAttribute(...)) expression within the for statement - it'll cause it to be evaluated every iteration. Calculate it once outside the loop and store it in a variable. There's a few other places where you're repeating calls unnecessarily, e.g. window.location.pathname.split()

EDIT: My answer discusses the issue but see Alnitak answer for a much better solution.
The get in getLikeURLs and the put in likeLinks are both asynchronous. The calls to both of these function return immediately. When data is returned from the called server at some indeterminate time later, the callback functions are then called. The puts could return before the gets which would be a problem in your case. Also note that JavaScript is NOT multi-threaded so the two methods, getLikeURLs and likeLinks will never run at the same time. The callback functions, on the other hand, might be called at anytime later with no guarantee as to the call back order. For example, the 3rd get/put might return before the 1st get/put in your loops.
You could use $.ajax to specify that the gets and puts are synchronous but this is ill advised because the browser will hang if ANY get/put doesn't return in a reasonable amount of time (e.g. server is offline). Plus you don't have the "multi-tasking" benefit of sending out a lot of requests and having the various servers working at the same time. They would do so serially.
The trick is to simply call likeLinks form the callback function in getLikeURL. Your case is a little tricky because of the for loop but this should work:
var links = [];
var url = '/' + window.location.pathname.split('/')[1] + '/' + window.location.pathname.split('/')[2] + '/'
getLikeURLs();
//likeLinks(); // Don't call yet. Wait for gets to all return.
function getLikeURLs() {
var returnCount = 0; // Initialize a callback counter.
var count = parseInt(document.getElementsByClassName('PageNav')[0].getAttribute('data-last')) + 1;
for (i = 0; i < count; i++) {
var link = $.get(url + 'page-' + (i + 1), function(data) {
//gets the like links from current page
$(data).find('a[class="LikeLink item control like"]').each(function() {
links.push($(this).attr('href')); // Puts the links in the Array
});
// If all gets have returned, call likeLinks.
returnCount++;
if (returnCount === count) {
likeLinks();
}
});
}
}
function likeLinks() {
for (t = 0; t <= links.length; t++) {
var token = document.getElementsByName('_xfToken')[0].getAttribute('value')
$.post(links[t], {
_xfToken: token,
_xfNoRedirect: 1,
_xfResponseType: 'json'
}, function(data) {});
}
}

Delay this Javascript FOR Loop

This LOOP queries the Parse.com server & then plays with the results if any. The problem is that when nArray is greater than 100, the function exceeds the query/burst limit of Parse.com CloudCode & it fails.
One idea would be to delay the LOOP for a second after every 100 LOOPS, but I'm not sure how to do that. Any other solutions would be greatly appreciated.
Thanks in Advance,
for (var k = 1; k < nArray.length; k++) {
(function (k, mArray) { // <-- define an inline function
query2.equalTo("username", nArray[k]); // BURST LIMIT EXCEEDS
query2.find({
success: function (results) {
if (results.length !== 0) {
var object = results[0];
var compareUserEmail = object.get('email');
if (compareUserEmail !== userEmail) {
// alert("The result is equal to" + object.get('Name'));
mArray.push({
name: object.get('Name'),
email: object.get('email'),
bloxID: object.get('bloxID')
});
gameScore.set("filtered", mArray);
gameScore.save(null, {
success: function (gameScore) {
response.success("Success!");
alert('New object created with objectId: ' + gameScore.id);
},
error: function (gameScore, error) {
alert('Failed to create new object, with error code: ' + error.description);
}
});
}
};
},
error: function () {}
});
})(k, mArray);
// <-- call it after definition using (k)
};

You've got a couple of issues to deal with.
The reason Parse.com doesn't support setInterval is because that would be inviting disaster. It terminates your Cloud Code if it takes too long, so letting you add delays would just increase the chance your code is terminated before completion.
The reason Parse.com has a burst limit is that this usually suggest "you are doing it wrong (tm)". In your case you are looping through an array and running a query for each item in the array. Instead you should be using the containedIn method to get all records for the array in one go. If you are getting more than 100 items in your array you can choose to increase the record limit to 1000, but first consider carefully if this is really what you need.
Given that you are modifying a lot of objects and saving them all, consider using the saveAll method to save them all in one hit too.
You might want to consider batching these operations, but be aware of the restrictions on overall duration for Cloud Code.

You can use a setInterval:
var i = 0;
var intervalId = setInterval(function() {
if(i < nArray.length) {
... your code ...
i++;
} else {
clearInterval(intervalId);
}
}, 100); //every 100ms; change it to what you need

DOM refresh on long running function

I have a button which runs a long running function when it's clicked. Now, while the function is running, I want to change the button text, but I'm having problems in some browsers like Firefox, IE.
html:
<button id="mybutt" class="buttonEnabled" onclick="longrunningfunction();"><span id="myspan">do some work</span></button>
javascript:
function longrunningfunction() {
document.getElementById("myspan").innerHTML = "doing some work";
document.getElementById("mybutt").disabled = true;
document.getElementById("mybutt").className = "buttonDisabled";
//long running task here
document.getElementById("myspan").innerHTML = "done";
}
Now this has problems in firefox and IE, ( in chrome it works ok )
So I thought to put it into a settimeout:
function longrunningfunction() {
document.getElementById("myspan").innerHTML = "doing some work";
document.getElementById("mybutt").disabled = true;
document.getElementById("mybutt").className = "buttonDisabled";
setTimeout(function() {
//long running task here
document.getElementById("myspan").innerHTML = "done";
}, 0);
}
but this doesn't work either for firefox! the button gets disabled, changes colour ( due to the application of the new css ) but the text does not change.
I have to set the time to 50ms instead of just 0ms, in order to make it work ( change the button text ). Now I find this stupid at least. I can understand if it would work with just a 0ms delay, but what would happen in a slower computer? maybe firefox would need 100ms there in the settimeout? it sounds rather stupid. I tried many times, 1ms, 10ms, 20ms...no it won't refresh it. only with 50ms.
So I followed the advice in this topic:
Forcing a DOM refresh in Internet explorer after javascript dom manipulation
so I tried:
function longrunningfunction() {
document.getElementById("myspan").innerHTML = "doing some work";
var a = document.getElementById("mybutt").offsetTop; //force refresh
//long running task here
document.getElementById("myspan").innerHTML = "done";
}
but it doesn't work ( FIREFOX 21). Then i tried:
function longrunningfunction() {
document.getElementById("myspan").innerHTML = "doing some work";
document.getElementById("mybutt").disabled = true;
document.getElementById("mybutt").className = "buttonDisabled";
var a = document.getElementById("mybutt").offsetTop; //force refresh
var b = document.getElementById("myspan").offsetTop; //force refresh
var c = document.getElementById("mybutt").clientHeight; //force refresh
var d = document.getElementById("myspan").clientHeight; //force refresh
setTimeout(function() {
//long running task here
document.getElementById("myspan").innerHTML = "done";
}, 0);
}
I even tried clientHeight instead of offsetTop but nothing. the DOM does not get refreshed.
Can someone offer a reliable solution preferrably non-hacky ?
thanks in advance!
as suggested here i also tried
$('#parentOfElementToBeRedrawn').hide().show();
to no avail
Force DOM redraw/refresh on Chrome/Mac
TL;DR:
looking for a RELIABLE cross-browser method to have a forced DOM refresh WITHOUT the use of setTimeout (preferred solution due to different time intervals needed depending on the type of long running code, browser, computer speed and setTimeout requires anywhere from 50 to 100ms depending on situation)
jsfiddle: http://jsfiddle.net/WsmUh/5/

Webpages are updated based on a single thread controller, and half the browsers don't update the DOM or styling until your JS execution halts, giving computational control back to the browser. That means if you set some element.style.[...] = ... it won't kick in until your code finishes running (either completely, or because the browser sees you're doing something that lets it intercept processing for a few ms).
You have two problems: 1) your button has a <span> in it. Remove that, just set .innerHTML on the button itself. But this isn't the real problem of course. 2) you're running very long operations, and you should think very hard about why, and after answering the why, how:
If you're running a long computational job, cut it up into timeout callbacks (or, in 2019, await/async - see note at the end of this anser). Your examples don't show what your "long job" actually is (a spin loop doesn't count) but you have several options depending on the browsers you take, with one GIANT booknote: don't run long jobs in JavaScript, period. JavaScript is a single threaded environment by specification, so any operation you want to do should be able to complete in milliseconds. If it can't, you're literally doing something wrong.
If you need to calculate difficult things, offload it to the server with an AJAX operation (universal across browsers, often giving you a) faster processing for that operation and b) a good 30 seconds of time that you can asynchronously not-wait for the result to be returned) or use a webworker background thread (very much NOT universal).
If your calculation takes long but not absurdly so, refactor your code so that you perform parts, with timeout breathing space:
function doLongCalculation(callbackFunction) {
var partialResult = {};
// part of the work, filling partialResult
setTimeout(function(){ doSecondBit(partialResult, callbackFunction); }, 10);
}
function doSecondBit(partialResult, callbackFunction) {
// more 'part of the work', filling partialResult
setTimeout(function(){ finishUp(partialResult, callbackFunction); }, 10);
}
function finishUp(partialResult, callbackFunction) {
var result;
// do last bits, forming final result
callbackFunction(result);
}
A long calculation can almost always be refactored into several steps, either because you're performing several steps, or because you're running the same computation a million times, and can cut it up into batches. If you have (exaggerated) this:
var resuls = [];
for(var i=0; i<1000000; i++) {
// computation is performed here
if(...) results.push(...);
}
then you can trivially cut this up into a timeout-relaxed function with a callback
function runBatch(start, end, terminal, results, callback) {
var i;
for(var i=start; i<end; i++) {
// computation is performed here
if(...) results.push(...); }
if(i>=terminal) {
callback(results);
} else {
var inc = end-start;
setTimeout(function() {
runBatch(start+inc, end+inc, terminal, results, callback);
},10);
}
}
function dealWithResults(results) {
...
}
function doLongComputation() {
runBatch(0,1000,1000000,[],dealWithResults);
}
TL;DR: don't run long computations, but if you have to, make the server do the work for you and just use an asynchronous AJAX call. The server can do the work faster, and your page won't block.
The JS examples of how to deal with long computations in JS at the client are only here to explain how you might deal with this problem if you don't have the option to do AJAX calls, which 99.99% of the time will not be the case.
edit
also note that your bounty description is a classic case of The XY problem
2019 edit
In modern JS the await/async concept vastly improves upon timeout callbacks, so use those instead. Any await lets the browser know that it can safely run scheduled updates, so you write your code in a "structured as if it's synchronous" way, but you mark your functions as async, and then you await their output them whenever you call them:
async doLongCalculation() {
let firstbit = await doFirstBit();
let secondbit = await doSecondBit(firstbit);
let result = await finishUp(secondbit);
return result;
}
async doFirstBit() {
//...
}
async doSecondBit...
...

SOLVED IT!! No setTimeout()!!!
Tested in Chrome 27.0.1453, Firefox 21.0, Internet 9.0.8112
$("#btn").on("mousedown",function(){
$('#btn').html('working');}).on('mouseup', longFunc);
function longFunc(){
//Do your long running work here...
for (i = 1; i<1003332300; i++) {}
//And on finish....
$('#btn').html('done');
}
DEMO HERE!

As of 2019 one uses double requesAnimationFrame to skip a frame instead of creating a race condition using setTimeout.
function doRun() {
document.getElementById('app').innerHTML = 'Processing JS...';
requestAnimationFrame(() =>
requestAnimationFrame(function(){
//blocks render
confirm('Heavy load done')
document.getElementById('app').innerHTML = 'Processing JS... done';
}))
}
doRun()
<div id="app"></div>
As an usage example think of calculating pi using Monte Carlo in an endless loop:
using for loop to mock while(true) - as this breaks the page
function* piMonteCarlo(r = 5, yield_cycle = 10000){
let total = 0, hits = 0, x=0, y=0, rsqrd = Math.pow(r, 2);
while(true){
total++;
if(total === Number.MAX_SAFE_INTEGER){
break;
}
x = Math.random() * r * 2 - r;
y = Math.random() * r * 2 - r;
(Math.pow(x,2) + Math.pow(y,2) < rsqrd) && hits++;
if(total % yield_cycle === 0){
yield 4 * hits / total
}
}
}
let pi_gen = piMonteCarlo(5, 1000), pi = 3;
for(let i = 0; i < 1000; i++){
// mocks
// while(true){
// basically last value will be rendered only
pi = pi_gen.next().value
console.log(pi)
document.getElementById('app').innerHTML = "PI: " + pi
}
<div id="app"></div>
And now think about using requestAnimationFrame for updates in between ;)
function* piMonteCarlo(r = 5, yield_cycle = 10000){
let total = 0, hits = 0, x=0, y=0, rsqrd = Math.pow(r, 2);
while(true){
total++;
if(total === Number.MAX_SAFE_INTEGER){
break;
}
x = Math.random() * r * 2 - r;
y = Math.random() * r * 2 - r;
(Math.pow(x,2) + Math.pow(y,2) < rsqrd) && hits++;
if(total % yield_cycle === 0){
yield 4 * hits / total
}
}
}
let pi_gen = piMonteCarlo(5, 1000), pi = 3;
function rAFLoop(calculate){
return new Promise(resolve => {
requestAnimationFrame( () => {
requestAnimationFrame(() => {
typeof calculate === "function" && calculate()
resolve()
})
})
})
}
let stopped = false
async function piDOM(){
while(stopped==false){
await rAFLoop(() => {
pi = pi_gen.next().value
console.log(pi)
document.getElementById('app').innerHTML = "PI: " + pi
})
}
}
function stop(){
stopped = true;
}
function start(){
if(stopped){
stopped = false
piDOM()
}
}
piDOM()
<div id="app"></div>
<button onclick="stop()">Stop</button>
<button onclick="start()">start</button>

As described in the "Script taking too long and heavy jobs" section of Events and timing in-depth (an interesting reading, by the way):
[...] split the job into parts which get scheduled after each other. [...] Then there is a “free time” for the browser to respond between parts. It is can render and react on other events. Both the visitor and the browser are happy.
I am sure that there are many times in which a task cannot be splitted into smaller tasks, or fragments. But I am sure that there will be many other times in which this is possible too! :-)
Some refactoring is needed in the example provided. You could create a function to do a piece of the work you have to do. It could begin like this:
function doHeavyWork(start) {
var total = 1000000000;
var fragment = 1000000;
var end = start + fragment;
// Do heavy work
for (var i = start; i < end; i++) {
//
}
Once the work is finished, function should determine if next work piece must be done, or if execution has finished:
if (end == total) {
// If we reached the end, stop and change status
document.getElementById("btn").innerHTML = "done!";
} else {
// Otherwise, process next fragment
setTimeout(function() {
doHeavyWork(end);
}, 0);
}
}
Your main dowork() function would be like this:
function dowork() {
// Set "working" status
document.getElementById("btn").innerHTML = "working";
// Start heavy process
doHeavyWork(0);
}
Full working code at http://jsfiddle.net/WsmUh/19/ (seems to behave gently on Firefox).

If you don't want to use setTimeout then you are left with WebWorker - this will require HTML5 enabled browsers however.
This is one way you can use them -
Define your HTML and an inline script (you don't have to use inline script, you can just as well give an url to an existing separate JS file):
<input id="start" type="button" value="Start" />
<div id="status">Preparing worker...</div>
<script type="javascript/worker">
postMessage('Worker is ready...');
onmessage = function(e) {
if (e.data === 'start') {
//simulate heavy work..
var max = 500000000;
for (var i = 0; i < max; i++) {
if ((i % 100000) === 0) postMessage('Progress: ' + (i / max * 100).toFixed(0) + '%');
}
postMessage('Done!');
}
};
</script>
For the inline script we mark it with type javascript/worker.
In the regular Javascript file -
The function that converts the inline script to a Blob-url that can be passed to a WebWorker. Note that this might note work in IE and you will have to use a regular file:
function getInlineJS() {
var js = document.querySelector('[type="javascript/worker"]').textContent;
var blob = new Blob([js], {
"type": "text\/plain"
});
return URL.createObjectURL(blob);
}
Setup worker:
var ww = new Worker(getInlineJS());
Receive messages (or commands) from the WebWorker:
ww.onmessage = function (e) {
var msg = e.data;
document.getElementById('status').innerHTML = msg;
if (msg === 'Done!') {
alert('Next');
}
};
We kick off with a button-click in this demo:
document.getElementById('start').addEventListener('click', start, false);
function start() {
ww.postMessage('start');
}
Working example here:
http://jsfiddle.net/AbdiasSoftware/Ls4XJ/
As you can see the user-interface is updated (with progress in this example) even if we're using a busy-loop on the worker. This was tested with an Atom based (slow) computer.
If you don't want or can't use WebWorker you have to use setTimeout.
This is because this is the only way (beside from setInterval) that allow you to queue up an event. As you noticed you will need to give it a few milliseconds as this will give the UI engine "room to breeth" so-to-speak. As JS is single-threaded you cannot queue up events other ways (requestAnimationFrame will not work well in this context).
Hope this helps.

Update: I don't think in the long term that you can be sure of avoiding Firefox's aggressive avoidance of DOM updates without using a timeout. If you want to force a redraw / DOM update, there are tricks available, like adjusting the offset of elements, or doing hide() then show(), etc., but there is nothing very pretty available, and after a while when those tricks get abused and slow down user experience, then browsers get updated to ignore those tricks. See this article and the linked articles beside it for some examples: Force DOM redraw/refresh on Chrome/Mac
The other answers look like they have the basic elements needed, but I thought it would be worthwhile to mention that my practice is to wrap all interactive DOM-changing functions in a "dispatch" function which handles the necessary pauses needed to get around the fact that Firefox is extremely aggressive in avoiding DOM updates in order to score well on benchmarks (and to be responsive to users while browsing the internet).
I looked at your JSFiddle and customized a dispatch function the one that many of my programs rely on. I think it is self-explanatory, and you can just paste it into your existing JS Fiddle to see how it works:
$("#btn").on("click", function() { dispatch(this, dowork, 'working', 'done!'); });
function dispatch(me, work, working, done) {
/* work function, working message HTML string, done message HTML string */
/* only designed for a <button></button> element */
var pause = 50, old;
if (!me || me.tagName.toLowerCase() != 'button' || me.innerHTML == working) return;
old = me.innerHTML;
me.innerHTML = working;
setTimeout(function() {
work();
me.innerHTML = done;
setTimeout(function() { me.innerHTML = old; }, 1500);
}, pause);
}
function dowork() {
for (var i = 1; i<1000000000; i++) {
//
}
}
Note: the dispatching function also blocks calls from happening at the same time, because it can seriously confuse users if status updates from multiple clicks are happening together.

Fake an ajax request
function longrunningfunction() {
document.getElementById("myspan").innerHTML = "doing some work";
document.getElementById("mybutt").disabled = true;
document.getElementById("mybutt").className = "buttonDisabled";
$.ajax({
url: "/",
complete: function () {
//long running task here
document.getElementById("myspan").innerHTML = "done";
}
});}

Try this
function longRunningTask(){
// Do the task here
document.getElementById("mybutt").value = "done";
}
function longrunningfunction() {
document.getElementById("mybutt").value = "doing some work";
setTimeout(function() {
longRunningTask();
}, 1);
}

Some browsers don't handle onclick html attribute good. It's better to use that event on js object. Like this:
<button id="mybutt" class="buttonEnabled">
<span id="myspan">do some work</span>
</button>
<script type="text/javascript">
window.onload = function(){
butt = document.getElementById("mybutt");
span = document.getElementById("myspan");
butt.onclick = function () {
span.innerHTML = "doing some work";
butt.disabled = true;
butt.className = "buttonDisabled";
//long running task here
span.innerHTML = "done";
};
};
</script>
I made a fiddle with working example http://jsfiddle.net/BZWbH/2/

Have you tried adding listener to "onmousedown" to change the button text and click event for longrunning function.

Slightly modified your code at jsfiddle and:
$("#btn").on("click", dowork);
function dowork() {
document.getElementById("btn").innerHTML = "working";
setTimeout(function() {
for (var i = 1; i<1000000000; i++) {
//
}
document.getElementById("btn").innerHTML = "done!";
}, 100);
}
Timeout set to more reasonable value 100ms did the trick for me. Try it.
Try adjusting the latency to find the best value.

DOM buffer also exists in default browser on android,
long running javascript only flush DOM buffer once,
use setTimeout(..., 50) to solve it.

I have adapted Estradiaz's double animation frame method for async/await:
async function waitForDisplayUpdate() {
await waitForNextAnimationFrame();
await waitForNextAnimationFrame();
}
function waitForNextAnimationFrame() {
return new Promise((resolve) => {
window.requestAnimationFrame(() => resolve());
});
}
async function main() {
const startTime = performance.now();
for (let i = 1; i <= 5; i++) {
setStatus("Step " + i);
await waitForDisplayUpdate();
wasteCpuTime(1000);
}
const elapsedTime = Math.round(performance.now() - startTime);
setStatus(`Completed in ${elapsedTime} ms`);
}
function wasteCpuTime(ms) {
const startTime = performance.now();
while (performance.now() < startTime + ms) {
if (Math.random() == 0) {
console.log("A very rare event has happened.");
}
}
}
function setStatus(s) {
document.getElementById("status").textContent = s;
}
document.addEventListener("DOMContentLoaded", main);
Status: <span id="status">Start</span>