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What is the simplest way to alert when the DOM is finished painting new elements?

I just want to disable certain buttons and show a loading spinner until images are loaded.
This is a similar question- How to detect when an image has finished rendering in the browser (i.e. painted)?
I am new to javascript and am confused why there is not a simple way to determine this! Something similar to this-
document.addEventListener('readystatechange', event => {
if (event.target.readyState === 'complete') {
alert('complete');
}
});
Unfortunately after much searching it seems I will need to use a callback or a promise. I figured it would be a good time to learn about promises/async/await. I am having difficulty attempting to rewrite my functions using promises.
$('#container').on('click', '#imgSearch', function (e) {
$(this).html(`
<i class="fa fa-spinner fa-spin"></i>Loading`);
//various if statements here to check radio buttons
showImgs(search, sort, phpController, limit);
}
function showImgs(search, sort, phpController, limit) {
imgArray = [];
var a1 = $.post(phpController, {search: search, sort: sort, limit: limit}, {dataType: 'json'});
$.when(a1).done(function (response) {
if (response['error']) {
alert(response.error.img);
} else {
var imgs = response;
if (Array.isArray(imgs)) {
for (let i = 0; i < imgs.length; i++) {
//I use setTimeout here to render one image per second
setTimeout(function () {
offset++;
saveImages(imgs[i]);
//calling alertFinished on last img is my temporary solution to removing spinner after render
if (i === imgs.length - 1) {
alertFinished();
}
}, 1000 * i);
}
} else {
saveImages(imgs);
}
}
});
}
;
I use the saveImages function to empty and push to another array as well as other purposes not shown-
function saveImages(img) {
imgArray = [];
imgArray.push(img);
displayImages(imgArray);
}
;
displayImages renders the image while adding classes etc.-
function displayImages(imgs) {
var counter = 0;
imgs.forEach(img => {
var html = '';
html += `<div class="" id='${img.id}'><img src=${img.image}></div>`;
$(html).hide().appendTo(imgSection).fadeIn(1000);
});
}
;
AlertFinished removes the loading spinner from search button.
function alertFinished() {
$('#imgSearch').text('Search');
}
Will someone please explain how I can use promises/async/await in this context? It's unfortunate there isn't a way to use an event listener similar to readystatechange because the alternative is to refactor every function that renders new elements in the DOM in order to disable buttons, show spinner etc. Showing a spinner/loading msg is such a widespread feature I am surprised I am having difficulty implementing it appropriately.

So first off, as you can see from the question you linked to (and comments therein), there isn't a great way to tell when an image is actually painted. So I'll focus on a way you can call some function after images are loaded.
For starters, if you have a bunch of images in your page right as it first loads, and you just want to wait for them to load before doing something, you could try the super simple route which would be the window load event.
window.addEventListener('load', (event) => {
// do stuff
});
But I get the impression you have a situation where you're adding images dynamically and want to do something after they're loaded, so that won't work. Still, you're overcomplicating things, I think. A quick look at your function shows you're calling saveImages and displayImages inside a loop even though they appear to be things you want to do only once after you're done adding images.
Assuming that at some point in your whole process you find yourself with a bunch of images that have been added to your DOM, at least some of which are still in the middle of loading, what you need to do is check for the last image to be loaded and then remove your loading spinner afterwards.
The trick here is figuring out which image is last to load. It won't necessarily be the last one you added because images added earlier on could be larger.
One approach you can use to skip the whole promise/async confusion all together would be to use a recursive function that every so often checks whether all images are loaded and if not waits a bit and then checks again. If you make the wait before the function calls itself again relatively short, this will likely work just fine for you.
Something along these lines:
const registeredImages = [];
// add your images
for (let i = 0, l = someImages.length; i < l; i += 1) {
doSomething(); // add someImages[i] to DOM where you want it
someImages[i].setAttribute('data-id', `image-${i}`); // or whatever way to keep track of it
someImages[i].addEventListener('load', register);
}
// remove spinner once they're loaded
tryToRemoveSpinner();
function register(event) {
images.push(event.target.getAttribute('data-id');
}
function tryToRemoveSpinner {
if (registeredImages.length === someImages.length) {
removeSpinner(); // or whatever
} else {
setTimeout(() => { tryToRemoveSpinner() }, 100);
}
}
An enhancement you could add here would be to put some kind of counter on tryToRemoveSpinner so if some image fails to load for whatever reason it eventually just bails out or runs removeSpinner() anyway or whatever you want to do in the event of an error, just in case.
Related reading: How to create a JavaScript callback for knowing when an image is loaded

How to dynamic load Jquery inside a JavaScript Class constructor and proceed the execution only after jquery has been fully loaded

This is actually a merge of three differents questions already all well answered here on stack overflow !
1 - How to Dynamic Load a JavaScript file from inside a Js Script :
2 - How to Dynamic Load Jquery
3 - SetTimeout inside a JS Class using this
Basically, I am building a class that will inject some pages inside my clients's website.
To do so, the client just need to add my script src on the page.
<script src="<my_pub_http_address>/MyClass.js">
Once the script is invoked, I will need jquery to continue the execution !
But, I cannot know if the website that invoked the scripts has jquery already loaded.
So, I need to check if jquery is loaded, if not, I will have to load it, append to head and only then when jquery is loaded and working, I will proceed with the script's execution .
PS: this is a kind of legacy answer ! I already had the solution beforehand !
So, any improvement will be appreciated !

That's the solution I've found:
// MyClass.js
var counterLoopLoad = 0;
class MyClass {
constructor(){
// do the code that does not need jQuery
return this.Init()
}
JqueryLoader() {
// Loop Breaker
counterLoopLoad ++;
if (counterLoopLoad == 100) {
throw 'I need jQuery in order to do what I am suppose to do!';
}
var __jquery = document.createElement('script');
__jquery.src = "http://code.jquery.com/jquery-latest.min.js";
__jquery.type = 'text/javascript';
// if needed ....
// __jquery.onload = function() {
// some code here
//
// };
// must be prepend !!! append won't work !!!!
document.head.prepend(__jquery);
// here is the point that makes all work !!!!
// without setTimeOut, the script will get in a loop !
var that = this;
setTimeout(function () {
that.Init();
}, 500);
}
Init() {
if (typeof jQuery == 'undefined') {
return this.JqueryLoader();
}
jQuery.ajax(...);
}
}

Concurrence problems with Javascript - I need a way to check if a file loading has finished

Hello stackoverflow users and readers,
I am programming a quite easy thing with JS for Firefox/Gecko 2.x and have reached a problem that is a little far away from my knowledge.
The thing is: I read a the content of a file to a string using the following code:
NetUtil.asyncFetch(my_file, function(inputStream, status) {
if (!Components.isSuccessCode(status)) {
return;
}
my_string = NetUtil.readInputStreamToString(inputStream, inputStream.available());
]);
And right after reading the file I evaluate the following condition:
if (my_string.length == 0) {
//do something...
} else {
//do something else...
}
OK, so the problem is, although there are some characters in the file, if it's the first run of the script, it will always go to the first condition because it hasn't got time enough to read the file and load the characters into the string. On a second run, the global variable my_string has the previously acquired value, so it will go into the "else" condition.
The question is: How can I listen to a "file finished loading" event in JavaScript to prevent this behaviour?
Thank you very much.

as far as fetch is async it's normal my_string to be empty. You need to subscribe for some custom event or pass a callback somehow.
NetUtil.asyncFetch(my_file, function(inputStream, status) {
if (!Components.isSuccessCode(status)) {
return;
}
my_string = NetUtil.readInputStreamToString(inputStream, inputStream.available());
var evt = document.createEvent('Event');
evt.initEvent('inputReady', true, true);
evt.my_string = my_string;
document.dispatchEvent(evt);
});
and then subscribe for this event
document.addEventListener('inputReady', function(e){
alert(e.my_string);
});
P.S. Not tested

hello i am not familiar with NetUtil of Firefox/Gecko 2.x but the concept look familiar.
i assume that is because the
NetUtil.asyncFetch
call to your callback function after the
if (my_string.length == 0) {
//do something...
} else {
//do something else...
}
why not you try using the data in correct place
NetUtil.asyncFetch(my_file, function(inputStream, status) {
if (!Components.isSuccessCode(status)) {
return;
}
my_string = NetUtil.readInputStreamToString(inputStream, inputStream.available());
alert(my_string.length); //is here is also be 0 ???????
//do some stuff with the data
]);

How to make my function to be page specific or div id specific?

I am writing javascript to my web pages, but there is a number of functions and loops, that i think are running in all pages, so the first one is running and failing on the second page. Because of this, the javascript function on the second page is not running.
Can anyone give me an idea of how to create page-specific functions or check the availability of an id? I don't use any frameworks.
thanks in advance.
my javascript code is :
window.onload = function(){
var yellows = document.getElementById('magazine-brief').getElementsByTagName('h2');
var signUp = document.getElementById('signup-link');
function animeYellowBar(num){
setTimeout(function(){
yellows[num].style.left = "0";
if(num == yellows.length-1){
setTimeout(function(){
signUp.style.webkitTransform = "scale(1)";
},num * 250);
}
}, num * 500);
}
for (var i = 0; i < yellows.length; i++){
animeYellowBar(i);
}
alert("alert second page");
}
in this code, the alert message not working on second page. any idea?

If I understand you correctly, you have a javascript function, that you want to attach to an event from a specific div element in your page.
a) Include an event directly to you HTML page, something like this:
<div id="element" onclick="some_function();">Text is here</div>
b) Use a javascript function (add this code between <script> tag):
window.onload = function() {
document.getElementById("element").setAttribute("onclick", "some_function()")
}

The best way would be to only include those scripts on the pages which need them. Why waste time loading and parsing scripts you don't need?
If you must keep them on every page, put your functions in an if statement and check for something unique to the page that needs them (such as a form element or field ID).
Update
In response to your comment:
You have to code more defensively. You are attempting to make use of the magazine-brief and signup-link elements before you have made certain that they exist. Never trust that the proper element was returned - always check that it was before attempting to use that element.
I suggest checking your vars like so:
var yellows = document.getElementById('magazine-brief').getElementsByTagName('h2');
var signUp = document.getElementById('signup-link');
if (yellows != 'undefined' && signUp != undefined)
{
function animeYellowBar(num)
{
//...
}
}

How to implement `using` in javascript?

I would like to make something like this (similar to c#):
using("content/jquery.js");
$("div").fadeOut();
So if content/jquery.js is not on a script in the head I would like to load it and continue the execution after it loads.
Is it possible to implement this or something similar? Note: I could have more than 1 using

These are called script loaders.
You can take a look at RequireJS, which behaves in a very similar way:
require(["helper/util"], function() {
//This function is called when scripts/helper/util.js is loaded.
});
There's also LabJS and ControlJS, which are more focused on async script loading rather than dependencies, but may be worth checking out. Also in this category, our very own #jAndy's SupplyJS.

You can use getScript:
$.getScript('test.js', function() {
alert('Load was performed.');
});

If you know the name of the functions you'll be calling ahead of time you can use typeof to check for their presence:
if (typeof($) == 'function') {
// Code here that uses jQuery
} else {
// Something else here that loads the script.
}
If you're not certain what functions you'll be using you probably want to retrieve a list of the script elements and check them. Something more along these lines:
var scripts = document.getElementsByTagName('script');
for (var i = 0, l = scripts.length; i < l; ++i) {
if (scripts[i].src == myVal) {
// do something here
} else {
// wait for the script to load, or just leave off the else.
}
}
Are the two approaches I can think of off the top of my head.