We Keep Coding

Sending message from background script to content script (multiple browsers)

I have a working prototype of an extension that works on Chrome but when I try to run it on Firefox i get the following error:
Unchecked lastError value: Error: Could not establish connection. Receiving end does not exist.
I use this code to differentiate between browsers:
window.namespace = (function () {
return window.msBrowser ||
window.browser ||
window.chrome;
})();
the following part is to detect when the user clicks on the extension icon (so that I know to activate it):
let show_floater = false; // to know if extension should be active
window.namespace.browserAction.onClicked.addListener(function(tab) {
buttonClicked(tab);
});
function buttonClicked(tab) {
show_floater = !show_floater;
console.log('coding intensifies');
// Send message to content_script of tab.id
window.namespace.tabs.sendMessage(tab.id, show_floater); // <-- ERROR IS HERE
}
All this code is in my background script.
The handling of the message in my content script is as follows
window.namespace.runtime.onMessage.addListener(gotMessage);
let injected = false;
function gotMessage(show_floater, sender, sendResponse) {
// Here I just do stuff
console.log("I'm working here!");
}
Online I saw that people that had this problem usually did not include <all_urls> in the manifest. In my case I already had that so I'm kinda lost here. From my understanding both Chrome and Firefox should use the same methods to send and receive messages. Is my way of distinguishing between browsers flawed?
CHANGES
Here I found a solution.
Background:
chrome.browserAction.onClicked.addListener(function (event) {
chrome.tabs.executeScript(null, {
file: 'js/content.js', /* my content script */ }, () => {
connect() //this is where I call my function to establish a
connection });
});
});
function connect() {
chrome.tabs.query({ active: true, currentWindow: true }, (tabs) => {
const port = chrome.tabs.connect(tabs[0].id);
show_floater = !show_floater;
port.postMessage(show_floater);
// port.onMessage.addListener((response) => {
// html = response.html;
// title = response.title;
// description = response.description;
// });
});
contentscript:
chrome.runtime.onConnect.addListener((port) => {
port.onMessage.addListener((show_floater) => {
else if (!injected) {
injected = true;
let link = document.createElement("link");
link.className = 'beebole_css';
link.href = "https://localhost/css/test.css";
link.type = "text/css";
link.rel = "stylesheet";
document.querySelector("head").appendChild(link);
let s = document.createElement("script");
s.className = 'beebole_js';
s.src = "https://localhost/js/test.js";
s.type = 'text/javascript';
// document.body.appendChild(s);
document.querySelector('body').appendChild(s);
}
});
});
Again, this code works perfectly on Chrome but on Firefox it give the following error:
Loading failed for the <script> with source “https://localhost/js/test.js”.

I suggest you use https://github.com/mozilla/webextension-polyfill for cross browser compatibility.

fingerprintjs not loading in chrome extension

I am trying to load fingerprintjs in my chrome extension and for some reason it is not loading.
The documentation says to use this approach, which works fine in standalone web sites, just not in chrome extensions
<script>
function initFingerprintJS() {
FingerprintJS.load().then(fp => {
// The FingerprintJS agent is ready.
// Get a visitor identifier when you'd like to.
fp.get().then(result => {
// This is the visitor identifier:
const visitorId = result.visitorId;
console.log("visitorId", visitorId);
});
});
}
</script>
<script async src="fp.min.js" onload="initFingerprintJS();"></script>
For chrome extension I added created a JS file initFingerprint.js that holds the init code like so:
var visitorId = null; //will hold the actual fingerprint
function initFingerprintJS() {
console.log("inside initFingerprintJS");
FingerprintJS.load().then(fp => {
console.log("loaded initFingerprintJS");
fp.get().then(result => {
console.log("initFingerprintJS got result", result)
visitorId = result.visitorId; // This is the visitor identifier
console.log("visitorId", visitorId);
});
});
}
initFingerprintJS();
In background.html, I added this:
<script async src="fp.min.js"></script>
<script async src="initFingerprint.js"></script>
I have tried with async in there and not in there, but still no luck. This line will print, but none of the other lines below it.
inside initFingerprintJS
What am I doing wrong? I appreciate any help. thank you

Remove <script> tag for fp.min.js from the html and create the script element yourself in initFingerprint.js so you can use the onload event directly:
loadScript('fp.min.js').then(initFingerprintJS);
function loadScript(url) {
return new Promise((resolve, reject) => {
const el = document.createElement('script');
el.onload = resolve;
el.onerror = reject;
el.src = url;
document.documentElement.appendChild(el);
});
}
async function initFingerprintJS() {
visitorId = await (await FingerprintJS.load()).get();
console.log('visitorId', visitorId);
}

How do I load a page and immediately edit the DOM in electron?

I'm trying to create a markdown editor.
So far: I have loaded the index page. I'm using fs.readdir to get the titles of all the markdown files and display them in the sidebar. Then, on clicking on of these title #content get's the content.
module.exports = (win) => {
fs.readdir( './data', (err, data) =>{
data.map(title => {
if(title.split('.md').length==2){
el = document.createElement("li"); // get gave it the title ..
el.addEventListener('click', function(e){
fs.readFile(`./data/${title}`, (err, data) => {
document.getElementById('content').innerHTML = data;
});
})
document.getElementById('titles').appendChild(el) // title are on the page
The problem is when I introduce another page
I have a preferences page
win.loadURL(path.join('file://', __dirname, '../static/preferences.html'))
It has the same sidebar, hence I import the same code to get the titles. But now when I click one of the links, I don't want document.getElementById('content').innerHTML = data; but I want to load the index page and then inject the content
So far I tried this
const checkPageState = (pageName, callback) => {
if(pageName === "preferences"){
ipcRenderer.send(GO_TO_PAGE, 'index')
}
setTimeout(callback(), 1000);
}
...
el.addEventListener('click', function(e){
checkPageState(win, ()=>{
fs.readFile(`./data/${title}`, (err, data) => {
if (err) throw err;
fileDir = `./data/${title}`;
document.getElementById('content').innerHTML = data;
});
})
})
My thinking was ipcRenderer.send(GO_TO_PAGE, 'index') would load the index page (which it does) when wait for a bit and then inject the data into the index page. It doesn't!
How can I do this?

I recently tried to do this as well and it was kinda tricky but I found something that worked:
In electron when it tries to go to another page I stop it from going to it with:
win.webContents.on('will-navigate', function (evt, url) {
evt.preventDefault();
win.webContents.executeJavaScript('makeHiddenPageIframe("' + url + '");');
});
Then it calls the makeHiddenPageIframe function defined on the page.
Then in the page I define the makeHiddenPageIframe function:
function makeHiddenPageIframe (url) {
var hiddenPage = document.createElement("iframe");
hiddenPage.setAttribute("src", url);
hiddenPage.style.display = 'none';
document.body.appendChild(hiddenPage);
hiddenPage.onload = function () {
var frameDocument = hiddenPage.document;
if (hiddenPage.contentDocument) {
frameDocument = hiddenPage.contentDocument;
} else if (hiddenPage.contentWindow) {
frameDocument = hiddenPage.contentWindow.document;
}
document.open();
document.write(frameDocument.documentElement.innerHTML);
document.close();
window.history.pushState("", document.title, url.replace('https://' + window.location.hostname, ''));
}
}
This then makes a iframe and loads the page in there then once it has loaded copy all the html from the iframe to the parent window so it seems like the switch happened instantly.
Also the window.history.pushState thing at the bottom was when you overwrite the html the url stays the same so when you reload it goes back to the original page but the window.history.pushState changes the url without reloading the page.
Any form of navigation will do the iframe load so you would keep your win.loadURL( to go to another markdown page.
The 'will-navigate' event docs.
window.history.pushState ref.
I hope this helps :)

Update class data when using event listener

I'm building a simple drawing app.
Let's say I have 4 classes:
App.js handles the communication between the classes
Pixels.js stores the image data
Display.js displays the data
Load.js loads in data
Usually from within the App class, I can do something like
$('#icon-flip').mouseup((e) =>
{
this.pixels.flip_pixels();
this.display.update(this.pixels.get_pixels());
});
Now I've added a Load class and my problem is that I don't know how to let the App class know that the data was completely loaded and processed, as the Load class should not know about the App class.
This is the Load class
class Load
{
constructor(config)
{
this.config = config;
this.setup_load_input();
}
setup_load_input()
{
let element = document.createElement('div');
element.innerHTML = '<input type="file" id="input-load" style="display: none">';
let fileInput = element.firstChild;
document.body.append(fileInput);
var that = this;
fileInput.addEventListener('change',function() { that.read_file_data(fileInput); });
}
read_file_data(fileInput)
{
var file = fileInput.files[0];
if (file.name.match(/\.(spm|json)$/))
{
var reader = new FileReader();
reader.onload = () =>
{
this.parse_file(reader.result);
};
reader.readAsText(file);
} else {
alert("File not supported, .spm or .json files only");
}
}
parse_file(file)
{
this.imported_file = JSON.parse(file);
}
get_imported_file()
{
return this.imported_file;
}
}
I trigger it from the App class with
$('#icon-load').mouseup((e) =>
{
$("#input-load").trigger("click");
});
After the data got loaded and parsed, I need to
this.pixels.update(this.load.get_imported_file());
this.display.update(this.pixels.get_pixels());
But I don't know how to do this as I don't know when the Load class finished processing the data. I figured the solution might be a callback, but since I'm a noob I don't know how.
I'm sorry for the long post and bad code quality. Thanks for any helpful support!

You could pass in an event handler to Load? For example:
/* App.js */
function updateThings() {
this.pixels.flip_pixels();
this.display.update(this.pixels.get_pixels());
}
// then later...
new Load({ onLoad: updateThings.bind(this) });
/* Load.js */
// In read_file_data()...
reader.onload = () => {
this.parse_file(reader.result);
this.config.onLoad();
};

load scripts asynchronously

I am using several plugins, custom widgets and some other libraries from JQuery. as a result I have several .js and .css files. I need to create a loader for my site because it takes some time to load. it will be nice if I can display the loader before importing all the:
<script type="text/javascript" src="js/jquery-1.6.2.min.js"></script>
<script type="text/javascript" src="js/myFunctions.js"></script>
<link type="text/css" href="css/main.css" rel="stylesheet" />
...
....
etc
I have found several tutorials that enable me to import a JavaScript library asynchronously. for example I can do something like:
(function () {
var s = document.createElement('script');
s.type = 'text/javascript';
s.async = true;
s.src = 'js/jquery-ui-1.8.16.custom.min.js';
var x = document.getElementsByTagName('script')[0];
x.parentNode.insertBefore(s, x);
})();
for some reason when I do the same thing for all my files the pages does not work. I have been trying for so long to try to find where the problem is but I just cannot find it. First I thought that it was probably because some javascript functions depended on the others. but I loaded them in the right order using the time out function when one completed I proceeded with the next and the page still behaves weird. for example I am not able to click on links etc... animations still work though..
Anyways
Here is what I have been thinking... I believe browsers have a cache that's why it takes a long time to load the page for the first time and the next time it is quick. so what I am thinking of doing is replacing my index.html page with a page that loads all this files asynchronously. when ajax is done loading all those files redirect to the page that I plan on using. when using that page it should not take long to load since the files should alredy be included on the cache of the browser. on my index page (page where .js and .css file get loaded asynchronously) I don't care of getting errors. I will just be displaying a loader and redirecting the page when done...
Is this idea a good alternative? or should I keep trying on implementing the asynchronously methods?
EDIT
the way I load everything async is like:
importScripts();
function importScripts()
{
//import: jquery-ui-1.8.16.custom.min.js
getContent("js/jquery-1.6.2.min.js",function (code) {
var s = document.createElement('script');
s.type = 'text/javascript';
//s.async = true;
s.innerHTML=code;
var x = document.getElementsByTagName('script')[0];
x.parentNode.insertBefore(s, x);
setTimeout(insertNext1,1);
});
//import: jquery-ui-1.8.16.custom.min.js
function insertNext1()
{
getContent("js/jquery-ui-1.8.16.custom.min.js",function (code) {
var s = document.createElement('script');
s.type = 'text/javascript';
s.innerHTML=code;
var x = document.getElementsByTagName('script')[0];
x.parentNode.insertBefore(s, x);
setTimeout(insertNext2,1);
});
}
//import: jquery-ui-1.8.16.custom.css
function insertNext2()
{
getContent("css/custom-theme/jquery-ui-1.8.16.custom.css",function (code) {
var s = document.createElement('link');
s.type = 'text/css';
s.rel ="stylesheet";
s.innerHTML=code;
var x = document.getElementsByTagName('script')[0];
x.parentNode.insertBefore(s, x);
setTimeout(insertNext3,1);
});
}
//import: main.css
function insertNext3()
{
getContent("css/main.css",function (code) {
var s = document.createElement('link');
s.type = 'text/css';
s.rel ="stylesheet";
s.innerHTML=code;
var x = document.getElementsByTagName('script')[0];
x.parentNode.insertBefore(s, x);
setTimeout(insertNext4,1);
});
}
//import: jquery.imgpreload.min.js
function insertNext4()
{
getContent("js/farinspace/jquery.imgpreload.min.js",function (code) {
var s = document.createElement('script');
s.type = 'text/javascript';
s.innerHTML=code;
var x = document.getElementsByTagName('script')[0];
x.parentNode.insertBefore(s, x);
setTimeout(insertNext5,1);
});
}
//import: marquee.js
function insertNext5()
{
getContent("js/marquee.js",function (code) {
var s = document.createElement('script');
s.type = 'text/javascript';
s.innerHTML=code;
var x = document.getElementsByTagName('script')[0];
x.parentNode.insertBefore(s, x);
setTimeout(insertNext6,1);
});
}
//import: marquee.css
function insertNext6()
{
getContent("css/marquee.css",function (code) {
var s = document.createElement('link');
s.type = 'text/css';
s.rel ="stylesheet";
s.innerHTML=code;
var x = document.getElementsByTagName('script')[0];
x.parentNode.insertBefore(s, x);
setTimeout(insertNext,1);
});
}
function insertNext()
{
setTimeout(pageReadyMan,10);
}
}
// get the content of url and pass that content to specified function
function getContent( url, callBackFunction )
{
// attempt to create the XMLHttpRequest and make the request
try
{
var asyncRequest; // variable to hold XMLHttpRequest object
asyncRequest = new XMLHttpRequest(); // create request object
// register event handler
asyncRequest.onreadystatechange = function(){
stateChange(asyncRequest, callBackFunction);
}
asyncRequest.open( 'GET', url, true ); // prepare the request
asyncRequest.send( null ); // send the request
} // end try
catch ( exception )
{
alert( 'Request failed.' );
} // end catch
} // end function getContent
// call function whith content when ready
function stateChange(asyncRequest, callBackFunction)
{
if ( asyncRequest.readyState == 4 && asyncRequest.status == 200 )
{
callBackFunction(asyncRequest.responseText);
} // end if
} // end function stateChange
and the weird part is that all the style's work plus all the javascript functions. the page is frozen for some reason though...

A couple solutions for async loading:
//this function will work cross-browser for loading scripts asynchronously
function loadScript(src, callback)
{
var s,
r,
t;
r = false;
s = document.createElement('script');
s.type = 'text/javascript';
s.src = src;
s.onload = s.onreadystatechange = function() {
//console.log( this.readyState ); //uncomment this line to see which ready states are called.
if ( !r && (!this.readyState || this.readyState == 'complete') )
{
r = true;
callback();
}
};
t = document.getElementsByTagName('script')[0];
t.parentNode.insertBefore(s, t);
}
If you've already got jQuery on the page, just use:
$.getScript(url, successCallback)*
Additionally, it's possible that your scripts are being loaded/executed before the document is done loading, meaning that you'd need to wait for document.ready before events can be bound to the elements.
It's not possible to tell specifically what your issue is without seeing the code.
The simplest solution is to keep all of your scripts inline at the bottom of the page, that way they don't block the loading of HTML content while they execute. It also avoids the issue of having to asynchronously load each required script.
If you have a particularly fancy interaction that isn't always used that requires a larger script of some sort, it could be useful to avoid loading that particular script until it's needed (lazy loading).
* scripts loaded with $.getScript will likely not be cached
For anyone who can use modern features such as the Promise object, the loadScript function has become significantly simpler:
function loadScript(src) {
return new Promise(function (resolve, reject) {
var s;
s = document.createElement('script');
s.src = src;
s.onload = resolve;
s.onerror = reject;
document.head.appendChild(s);
});
}
Be aware that this version no longer accepts a callback argument as the returned promise will handle callback. What previously would have been loadScript(src, callback) would now be loadScript(src).then(callback).
This has the added bonus of being able to detect and handle failures, for example one could call...
loadScript(cdnSource)
.catch(loadScript.bind(null, localSource))
.then(successCallback, failureCallback);
...and it would handle CDN outages gracefully.

HTML5's new 'async' attribute is supposed to do the trick. 'defer' is also supported in most browsers if you care about IE.
async - The HTML
<script async src="siteScript.js" onload="myInit()"></script>
defer - The HTML
<script defer src="siteScript.js" onload="myInit()"></script>
While analyzing the new adsense ad unit code I noticed the attribute and a search lead me here: http://davidwalsh.name/html5-async

I loaded the scripts asynchronously (html 5 has that feature) when all the scripts where done loading I redirected the page to index2.html where index2.html uses the same libraries. Because browsers have a cache once the page redirects to index2.html, index2.html loads in less than a second because it has all it needs to load the page. In my index.html page I also load the images that I plan on using so that the browser place those images on the cache. so my index.html looks like:
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>Project Management</title>
<!-- the purpose of this page is to load all the scripts on the browsers cache so that pages can load fast from now on -->
<script type="text/javascript">
function stylesheet(url) {
var s = document.createElement('link');
s.type = 'text/css';
s.async = true;
s.src = url;
var x = document.getElementsByTagName('head')[0];
x.appendChild(s);
}
function script(url) {
var s = document.createElement('script');
s.type = 'text/javascript';
s.async = true;
s.src = url;
var x = document.getElementsByTagName('head')[0];
x.appendChild(s);
}
//load scritps to the catche of browser
(function () {
stylesheet('css/custom-theme/jquery-ui-1.8.16.custom.css');
stylesheet('css/main.css');
stylesheet('css/marquee.css');
stylesheet('css/mainTable.css');
script('js/jquery-ui-1.8.16.custom.min.js');
script('js/jquery-1.6.2.min.js');
script('js/myFunctions.js');
script('js/farinspace/jquery.imgpreload.min.js');
script('js/marquee.js');
})();
</script>
<script type="text/javascript">
// once the page is loaded go to index2.html
window.onload = function () {
document.location = "index2.html";
}
</script>
</head>
<body>
<div id="cover" style="position:fixed; left:0px; top:0px; width:100%; height:100%; background-color:Black; z-index:100;">Loading</div>
<img src="images/home/background.png" />
<img src="images/home/3.png"/>
<img src="images/home/6.jpg"/>
<img src="images/home/4.png"/>
<img src="images/home/5.png"/>
<img src="images/home/8.jpg"/>
<img src="images/home/9.jpg"/>
<img src="images/logo.png"/>
<img src="images/logo.png"/>
<img src="images/theme/contentBorder.png"/>
</body>
</html>
another nice thing about this is that I may place a loader in the page and when the page is done loading the loader will go away and in a matte of milliseconds the new page will be running.

Example from google
<script type="text/javascript">
(function() {
var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true;
po.src = 'https://apis.google.com/js/plusone.js?onload=onLoadCallback';
var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s);
})();
</script>

Several notes:
s.async = true is not very correct for HTML5 doctype, correct is s.async = 'async' (actually using true is correct, thanks to amn who pointed it out in the comment just below)
Using timeouts to control the order is not very good and safe, and you also make the loading time much larger, to equal the sum of all timeouts!
Since there is a recent reason to load files asynchronously, but in order, I'd recommend a bit more functional-driven way over your example (remove console.log for production use :) ):
(function() {
var prot = ("https:"===document.location.protocol?"https://":"http://");
var scripts = [
"path/to/first.js",
"path/to/second.js",
"path/to/third.js"
];
function completed() { console.log('completed'); } // FIXME: remove logs
function checkStateAndCall(path, callback) {
var _success = false;
return function() {
if (!_success && (!this.readyState || (this.readyState == 'complete'))) {
_success = true;
console.log(path, 'is ready'); // FIXME: remove logs
callback();
}
};
}
function asyncLoadScripts(files) {
function loadNext() { // chain element
if (!files.length) completed();
var path = files.shift();
var scriptElm = document.createElement('script');
scriptElm.type = 'text/javascript';
scriptElm.async = true;
scriptElm.src = prot+path;
scriptElm.onload = scriptElm.onreadystatechange = \
checkStateAndCall(path, loadNext); // load next file in chain when
// this one will be ready
var headElm = document.head || document.getElementsByTagName('head')[0];
headElm.appendChild(scriptElm);
}
loadNext(); // start a chain
}
asyncLoadScripts(scripts);
})();

Thanks to HTML5, you can now declare the scripts that you want to load asynchronously by adding "async" in the tag:
<script async>...</script>
Note: The async attribute is only for external scripts (and should only be used if the src attribute is present).
Note: There are several ways an external script can be executed:
If async is present: The script is executed asynchronously with the rest of the page (the script will be executed while the page continues the parsing)
If async is not present and defer is present: The script is executed when the page has finished parsing
If neither async or defer is present: The script is fetched and executed immediately, before the browser continues parsing the page
See this: http://www.w3schools.com/tags/att_script_async.asp

I wrote a little post to help out with this, you can read more here https://timber.io/snippets/asynchronously-load-a-script-in-the-browser-with-javascript/, but I've attached the helper class below. It will automatically wait for a script to load and return a specified window attribute once it does.
export default class ScriptLoader {
constructor (options) {
const { src, global, protocol = document.location.protocol } = options
this.src = src
this.global = global
this.protocol = protocol
this.isLoaded = false
}
loadScript () {
return new Promise((resolve, reject) => {
// Create script element and set attributes
const script = document.createElement('script')
script.type = 'text/javascript'
script.async = true
script.src = `${this.protocol}//${this.src}`
// Append the script to the DOM
const el = document.getElementsByTagName('script')[0]
el.parentNode.insertBefore(script, el)
// Resolve the promise once the script is loaded
script.addEventListener('load', () => {
this.isLoaded = true
resolve(script)
})
// Catch any errors while loading the script
script.addEventListener('error', () => {
reject(new Error(`${this.src} failed to load.`))
})
})
}
load () {
return new Promise(async (resolve, reject) => {
if (!this.isLoaded) {
try {
await this.loadScript()
resolve(window[this.global])
} catch (e) {
reject(e)
}
} else {
resolve(window[this.global])
}
})
}
}
Usage is like this:
const loader = new Loader({
src: 'cdn.segment.com/analytics.js',
global: 'Segment',
})
// scriptToLoad will now be a reference to `window.Segment`
const scriptToLoad = await loader.load()

I would complete zzzzBov's answer with a check for the presence of callback and allow passing of arguments:
function loadScript(src, callback, args) {
var s, r, t;
r = false;
s = document.createElement('script');
s.type = 'text/javascript';
s.src = src;
if (typeof(callback) === 'function') {
s.onload = s.onreadystatechange = function() {
if (!r && (!this.readyState || this.readyState === 'complete')) {
r = true;
callback.apply(args);
}
};
};
t = document.getElementsByTagName('script')[0];
t.parent.insertBefore(s, t);
}

Here is a great contemporary solution to the asynchronous script loading though it only address the js script with async false.
There is a great article written in www.html5rocks.com - Deep dive into the murky waters of script loading .
After considering many possible solutions, the author concluded that adding js scripts to the end of body element is the best possible way to avoid blocking page rendering by js scripts.
In the mean time, the author added another good alternate solution for those people who are desperate to load and execute scripts asynchronously.
Considering you've four scripts named script1.js, script2.js, script3.js, script4.js then you can do it with applying async = false:
[
'script1.js',
'script2.js',
'script3.js',
'script4.js'
].forEach(function(src) {
var script = document.createElement('script');
script.src = src;
script.async = false;
document.head.appendChild(script);
});
Now, Spec says: Download together, execute in order as soon as all download.
Firefox < 3.6, Opera says: I have no idea what this “async” thing is, but it just so happens I execute scripts added via JS in the order they’re added.
Safari 5.0 says: I understand “async”, but don’t understand setting it to “false” with JS. I’ll execute your scripts as soon as they land, in whatever order.
IE < 10 says: No idea about “async”, but there is a workaround using “onreadystatechange”.
Everything else says: I’m your friend, we’re going to do this by the book.
Now, the full code with IE < 10 workaround:
var scripts = [
'script1.js',
'script2.js',
'script3.js',
'script4.js'
];
var src;
var script;
var pendingScripts = [];
var firstScript = document.scripts[0];
// Watch scripts load in IE
function stateChange() {
// Execute as many scripts in order as we can
var pendingScript;
while (pendingScripts[0] && ( pendingScripts[0].readyState == 'loaded' || pendingScripts[0].readyState == 'complete' ) ) {
pendingScript = pendingScripts.shift();
// avoid future loading events from this script (eg, if src changes)
pendingScript.onreadystatechange = null;
// can't just appendChild, old IE bug if element isn't closed
firstScript.parentNode.insertBefore(pendingScript, firstScript);
}
}
// loop through our script urls
while (src = scripts.shift()) {
if ('async' in firstScript) { // modern browsers
script = document.createElement('script');
script.async = false;
script.src = src;
document.head.appendChild(script);
}
else if (firstScript.readyState) { // IE<10
// create a script and add it to our todo pile
script = document.createElement('script');
pendingScripts.push(script);
// listen for state changes
script.onreadystatechange = stateChange;
// must set src AFTER adding onreadystatechange listener
// else we’ll miss the loaded event for cached scripts
script.src = src;
}
else { // fall back to defer
document.write('<script src="' + src + '" defer></'+'script>');
}
}

for HTML5, you can use the 'prefetch'
<link rel="prefetch" href="/style.css" as="style" />
have a look at 'preload' for js.
<link rel="preload" href="used-later.js" as="script">

One reason why your scripts could be loading so slowly is if you were running all of your scripts while loading the page, like this:
callMyFunctions();
instead of:
$(window).load(function() {
callMyFunctions();
});
This second bit of script waits until the browser has completely loaded all of your Javascript code before it starts executing any of your scripts, making it appear to the user that the page has loaded faster.
If you're looking to enhance the user's experience by decreasing the loading time, I wouldn't go for the "loading screen" option. In my opinion that would be much more annoying than just having the page load more slowly.

I would suggest you take a look at Modernizr. Its a small light weight library that you can asynchronously load your javascript with features that allow you to check if the file is loaded and execute the script in the other you specify.
Here is an example of loading jquery:
Modernizr.load([
{
load: '//ajax.googleapis.com/ajax/libs/jquery/1.6.1/jquery.js',
complete: function () {
if ( !window.jQuery ) {
Modernizr.load('js/libs/jquery-1.6.1.min.js');
}
}
},
{
// This will wait for the fallback to load and
// execute if it needs to.
load: 'needs-jQuery.js'
}
]);

You might find this wiki article interesting : http://ajaxpatterns.org/On-Demand_Javascript
It explains how and when to use such technique.

Well, x.parentNode returns the HEAD element, so you are inserting the script just before the head tag. Maybe that's the problem.
Try x.parentNode.appendChild() instead.

Check out this https://github.com/stephen-lazarionok/async-resource-loader. It has an example that shows how to load JS, CSS and multiple files with one shot.

Have you considered using Fetch Injection? I rolled an open source library called fetch-inject to handle cases like these. Here's what your loader might look like using the lib:
fetcInject([
'js/jquery-1.6.2.min.js',
'js/marquee.js',
'css/marquee.css',
'css/custom-theme/jquery-ui-1.8.16.custom.css',
'css/main.css'
]).then(() => {
'js/jquery-ui-1.8.16.custom.min.js',
'js/farinspace/jquery.imgpreload.min.js'
})
For backwards compatibility leverage feature detection and fall-back to XHR Injection or Script DOM Elements, or simply inline the tags into the page using document.write.

Here is my custom solution to eliminate render-blocking JavaScript:
// put all your JS files here, in correct order
const libs = {
"jquery": "https://code.jquery.com/jquery-2.1.4.min.js",
"bxSlider": "https://cdnjs.cloudflare.com/ajax/libs/bxslider/4.2.5/jquery.bxslider.min.js",
"angular": "https://ajax.googleapis.com/ajax/libs/angularjs/1.5.0-beta.2/angular.min.js",
"ngAnimate": "https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.5.0-beta.2/angular-animate.min.js"
}
const loadedLibs = {}
let counter = 0
const loadAsync = function(lib) {
var http = new XMLHttpRequest()
http.open("GET", libs[lib], true)
http.onload = () => {
loadedLibs[lib] = http.responseText
if (++counter == Object.keys(libs).length) startScripts()
}
http.send()
}
const startScripts = function() {
for (var lib in libs) eval(loadedLibs[lib])
console.log("allLoaded")
}
for (var lib in libs) loadAsync(lib)
In short, it loads all your scripts asynchronously, and then executes them consequently.
Github repo: https://github.com/mudroljub/js-async-loader

Here a little ES6 function if somebody wants to use it in React for example
import {uniqueId} from 'lodash' // optional
/**
* #param {String} file The path of the file you want to load.
* #param {Function} callback (optional) The function to call when the script loads.
* #param {String} id (optional) The unique id of the file you want to load.
*/
export const loadAsyncScript = (file, callback, id) => {
const d = document
if (!id) { id = uniqueId('async_script') } // optional
if (!d.getElementById(id)) {
const tag = 'script'
let newScript = d.createElement(tag)
let firstScript = d.getElementsByTagName(tag)[0]
newScript.id = id
newScript.async = true
newScript.src = file
if (callback) {
// IE support
newScript.onreadystatechange = () => {
if (newScript.readyState === 'loaded' || newScript.readyState === 'complete') {
newScript.onreadystatechange = null
callback(file)
}
}
// Other (non-IE) browsers support
newScript.onload = () => {
callback(file)
}
}
firstScript.parentNode.insertBefore(newScript, firstScript)
} else {
console.error(`The script with id ${id} is already loaded`)
}
}

A concise answer, the explanations in the code
function loadScript(src) {
let script = document.createElement('script');
script.type = 'text/javascript';
script.src = src;
//
// script.async = false; // uncomment this line and scripts will be executed in the document order, like 'defer' option
//
// script.defer = true; // uncomment this line when scripts need whole DOM and/or relative order execution is important
//
// the script starts loading as it's append to the document and dynamic script behave as “async” by default
// other scripts don’t wait for 'async' scripts, and 'async' scripts don’t wait for them
// scripts that loads first – runs first (“load-first” order)
document.body.append(script);
}
loadScript('js/example01.js');
loadScript('js/example02.js');
/*
the 'defer' attribute tells the browser not to wait for the script
the 'async' attribute make script to load in the background and run when ready
the 'async' and 'defer' attribute are only for external scripts
'defer' is used for scripts that need the whole DOM and/or their relative execution order is important
'async' is used for independent scripts, like counters or ads, when their relative execution order does not matter
More: https://javascript.info/script-async-defer
*/

You can use LABJS or RequreJS
Script loaders like LABJS, RequireJS will improve the speed and quality of your code.

const dynamicScriptLoading = async (src) =>
{
const response = await fetch(src);
const dataResponse = await response.text();
eval.apply(null, [dataResponse]);
}

I would suggest looking into minifying the files first and see if that gives you a big enough speed boost. If your host is slow, could try putting that static content on a CDN.