Verify External Script Is Loaded

Verify External Script Is Loaded - javascript

I'm creating a jquery plugin and I want to verify an external script is loaded. This is for an internal web app and I can keep the script name/location consistent(mysscript.js). This is also an ajaxy plugin that can be called on many times on the page.
If I can verify the script is not loaded I'll load it using:
jQuery.getScript()
How can I verify the script is loaded because I don't want the same script loaded on the page more than once? Is this something that I shouldn't need to worry about due to caching of the script?
Update:
I may not have control over who uses this plugin in our organization and may not be able to enforce that the script is not already on the page with or without a specific ID, but the script name will always be in the same place with the same name. I'm hoping I can use the name of the script to verify it's actually loaded.

If the script creates any variables or functions in the global space you can check for their existance:
External JS (in global scope) --
var myCustomFlag = true;
And to check if this has run:
if (typeof window.myCustomFlag == 'undefined') {
//the flag was not found, so the code has not run
$.getScript('<external JS>');
}
Update
You can check for the existence of the <script> tag in question by selecting all of the <script> elements and checking their src attributes:
//get the number of `<script>` elements that have the correct `src` attribute
var len = $('script').filter(function () {
return ($(this).attr('src') == '<external JS>');
}).length;
//if there are no scripts that match, the load it
if (len === 0) {
$.getScript('<external JS>');
}
Or you can just bake this .filter() functionality right into the selector:
var len = $('script[src="<external JS>"]').length;

Few too many answers on this one, but I feel it's worth adding this solution. It combines a few different answers.
Key points for me were
add an #id tag, so it's easy to find, and not duplicate
Use .onload() to wait until the script has finished loading before using it
mounted() {
// First check if the script already exists on the dom
// by searching for an id
let id = 'googleMaps'
if(document.getElementById(id) === null) {
let script = document.createElement('script')
script.setAttribute('src', 'https://maps.googleapis.com/maps/api/js?key=' + apiKey)
script.setAttribute('id', id)
document.body.appendChild(script)
// now wait for it to load...
script.onload = () => {
// script has loaded, you can now use it safely
alert('thank me later')
// ... do something with the newly loaded script
}
}
}

#jasper's answer is totally correct but with modern browsers, a standard Javascript solution could be:
function isScriptLoaded(src)
{
return Boolean(document.querySelector('script[src="' + src + '"]'));
}
UPDATE July 2021:
The accepted solutions above have changed & improved much over time. The scope of my previous answer above was only to detect if the script was inserted in the document to load (and not whether the script has actually finished loading).
To detect if the script has already loaded, I use the following method (in general):
Create a common library function to dynamically load all scripts.
Before loading, it uses the isScriptLoaded(src) function above to check whether the script has already been added (say, by another module).
I use something like the following loadScript() function to load the script that uses callback functions to inform the calling modules if the script finished loading successfully.
I also use additional logic to retry when script loading fails (in case of temporary network issues).
Retry is done by removing the <script> tag from the body and adding it again.
If it still fails to load after configured number of retries, the <script> tag is removed from the body.
I have removed that logic from the following code for simplicity. It should be easy to add.
/**
* Mark/store the script as fully loaded in a global variable.
* #param src URL of the script
*/
function markScriptFullyLoaded(src) {
window.scriptLoadMap[src] = true;
}
/**
* Returns true if the script has been added to the page
* #param src URL of the script
*/
function isScriptAdded(src) {
return Boolean(document.querySelector('script[src="' + src + '"]'));
}
/**
* Returns true if the script has been fully loaded
* #param src URL of the script
*/
function isScriptFullyLoaded(src) {
return src in window.scriptLoadMap && window.scriptLoadMap[src];
}
/**
* Load a script.
* #param src URL of the script
* #param onLoadCallback Callback function when the script is fully loaded
* #param onLoadErrorCallback Callback function when the script fails to load
* #param retryCount How many times retry laoding the script? (Not implimented here. Logic goes into js.onerror function)
*/
function loadScript(src, onLoadCallback, onLoadErrorCallback, retryCount) {
if (!src) return;
// Check if the script is already loaded
if ( isScriptAdded(src) )
{
// If script already loaded successfully, trigger the callback function
if (isScriptFullyLoaded(src)) onLoadCallback();
console.warn("Script already loaded. Skipping: ", src);
return;
}
// Loading the script...
const js = document.createElement('script');
js.setAttribute("async", "");
js.src = src;
js.onload = () => {
markScriptFullyLoaded(src)
// Optional callback on script load
if (onLoadCallback) onLoadCallback();
};
js.onerror = () => {
// Remove the script node (to be able to try again later)
const js2 = document.querySelector('script[src="' + src +'"]');
js2.parentNode.removeChild(js2);
// Optional callback on script load failure
if (onLoadErrorCallback) onLoadErrorCallback();
};
document.head.appendChild(js);
}

This was very simple now that I realize how to do it, thanks to all the answers for leading me to the solution. I had to abandon $.getScript() in order to specify the source of the script...sometimes doing things manually is best.
Solution
//great suggestion #Jasper
var len = $('script[src*="Javascript/MyScript.js"]').length;
if (len === 0) {
alert('script not loaded');
loadScript('Javascript/MyScript.js');
if ($('script[src*="Javascript/MyScript.js"]').length === 0) {
alert('still not loaded');
}
else {
alert('loaded now');
}
}
else {
alert('script loaded');
}
function loadScript(scriptLocationAndName) {
var head = document.getElementsByTagName('head')[0];
var script = document.createElement('script');
script.type = 'text/javascript';
script.src = scriptLocationAndName;
head.appendChild(script);
}

Create the script tag with a specific ID and then check if that ID exists?
Alternatively, loop through script tags checking for the script 'src' and make sure those are not already loaded with the same value as the one you want to avoid ?
Edit: following feedback that a code example would be useful:
(function(){
var desiredSource = 'https://sitename.com/js/script.js';
var scripts = document.getElementsByTagName('script');
var alreadyLoaded = false;
if(scripts.length){
for(var scriptIndex in scripts) {
if(!alreadyLoaded && desiredSource === scripts[scriptIndex].src) {
alreadyLoaded = true;
}
}
}
if(!alreadyLoaded){
// Run your code in this block?
}
})();
As mentioned in the comments (https://stackoverflow.com/users/1358777/alwin-kesler), this may be an alternative (not benchmarked):
(function(){
var desiredSource = 'https://sitename.com/js/script.js';
var scripts = document.getElementsByTagName('script');
var alreadyLoaded = false;
for(var scriptIndex in document.scripts) {
if(!alreadyLoaded && desiredSource === scripts[scriptIndex].src) {
alreadyLoaded = true;
}
}
if(!alreadyLoaded){
// Run your code in this block?
}
})();

Simply check if the global variable is available, if not check again. In order to prevent the maximum callstack being exceeded set a 100ms timeout on the check:
function check_script_loaded(glob_var) {
if(typeof(glob_var) !== 'undefined') {
// do your thing
} else {
setTimeout(function() {
check_script_loaded(glob_var)
}, 100)
}
}

Another way to check an external script is loaded or not, you can use data function of jquery and store a validation flag. Example as :
if(!$("body").data("google-map"))
{
console.log("no js");
$.getScript("https://maps.googleapis.com/maps/api/js?v=3.exp&sensor=false&callback=initilize",function(){
$("body").data("google-map",true);
},function(){
alert("error while loading script");
});
}
}
else
{
console.log("js already loaded");
}

I think it's better to use window.addEventListener('error') to capture the script load error and try to load it again.
It's useful when we load scripts from a CDN server. If we can't load script from the CDN, we can load it from our server.
window.addEventListener('error', function(e) {
if (e.target.nodeName === 'SCRIPT') {
var scriptTag = document.createElement('script');
scriptTag.src = e.target.src.replace('https://static.cdn.com/', '/our-server/static/');
document.head.appendChild(scriptTag);
}
}, true);

Merging several answers from above into an easy to use function
function GetScriptIfNotLoaded(scriptLocationAndName)
{
var len = $('script[src*="' + scriptLocationAndName +'"]').length;
//script already loaded!
if (len > 0)
return;
var head = document.getElementsByTagName('head')[0];
var script = document.createElement('script');
script.type = 'text/javascript';
script.src = scriptLocationAndName;
head.appendChild(script);
}

My idead is to listen the error log if there is an error on script loading.
const checkSegmentBlocked = (e) => {
if (e.target.nodeName === 'SCRIPT' && e.target.src.includes('analytics.min.js')) {
window.isSegmentBlocked = true;
e.target.removeEventListener(e.type, checkSegmentBlocked);
}
};
window.addEventListener('error', checkSegmentBlocked, true);

Some answers on this page are wrong. They check for the existence of the <script> tag - but that is not enough. That tells you that the tag was inserted into the DOM, not that the script is finished loading.
I assume from the question that there are two parts: the code that inserts the script, and the code that checks whether the script has loaded.
The code that dynamically inserts the script:
let tag = document.createElement('script');
tag.type = 'text/javascript';
tag.id = 'foo';
tag.src = 'https://cdn.example.com/foo.min.js';
tag.onload = () => tag.setAttribute('data-loaded', true); // magic sauce
document.body.appendChild(tag);
Some other code, that checks whether the script has loaded:
let script = document.getElementById('foo');
let isLoaded = script && script.getAttribute('data-loaded') === 'true';
console.log(isLoaded); // true
If the both of those things (inserting and checking) are in the same code block, then you could simplify the above:
tag.onload = () => console.log('loaded');

I found a quick tip before you start diving into code that might save a bit of time. Check devtools on the webpage and click on the network tab. The js scripts are shown if they are loaded as a 200 response from the server.

Related

How to recognize that one js file loaded?

I try to display progress bar when page loading. I want change width of progress bar after js files loaded .At the final after load all documents set with of progress bar to 100% .Now I need to recognize js files loading with javascript.
Is this possible ? Please advice.

For internal js files loading recognition:
As functions and variables can be accessed from another file you can set the value of global progress variable and display it's value by calling the function
//on page or head js file
var progress = 0;
function displayProgress()
{
//show progress based on 'progress' variable
}
//file1.js
progress += 10;
displayProgress();
...
//file2.js
progress += 20;
displayProgress();
...
For external js files there is good article. The main idea is to periodically check existense of external functions (typeof fixpng =='function') and if it exist - stop checking and display progress.
Here's the JavaScript code to load the external library with a
callback passed in:
function loadExtScript(src, callback) { var s = document.createElement('script'); s.src = src; document.body.appendChild(s); // if loaded...call the callback }
Firefox allows you to listen for the onload event on the script
element:
s.onload = callback;
With Internet Explorer you can wait for a state change on the script
element:
s.onreadystatechange = function() { if ( this.readyState != "loaded"
) return; callback.call(); }
The problem comes with Safari - there's no event change for Safari, so
we can't tell when the script has loaded. This is the solution I came
up with (and this solution should also work with Opera):
function loadExtScript(src, test, callback) { var s =
document.createElement('script'); s.src = src;
document.body.appendChild(s);
var callbackTimer = setInterval(function() {
var call = false;
try {
call = test.call();
} catch (e) {}
if (call) {
clearInterval(callbackTimer);
callback.call();
} }, 100); }
The function takes a test as a parameter. Since you are the designer
of the app, you'll know what successful test is. Once this test is
true, it will execute the callback. A simple test could be to check
whether a function exists, for example:
loadExtScript('/fixpng.js', function() { return (typeof fixpng ==
'function'); }, myCallbackFunction);

If you know at least one defined namespace (almost all libraries and plugins have it: e.g. jQuery, jQuery.ui, jQuery.mobile, toastr, DataTable, etc.) or one global variable name introduced by the script files which are being loaded, then you can do this:
(function(undefined) {
var scriptFilesLoaded = false,
files = [],
timer = setInterval(function(){
try {
files = [
jQuery,
jQuery.mobile,
jQuery.ui,
someGlobalVariableName
];
if(files.indexOf(undefined)<0){
scriptFilesLoaded = true;
clearInterval(timer);
}
}
catch(e) {
console.warn('Preloader in action: Script files not loaded yet.');
}
},200);
})();
It doesn't matter if the script file is remote or local.

Error:Bootstrap's JavaScript requires jQuery

So i am working on a simple javascript widget and i started up by followinf this tutorial. I am loading jquery dynamically like below:
if (window.jQuery === undefined || window.jQuery.fn.jquery !== '2.1.4') {
UPDATE, Here is how i'm loading jQuery
var script_tag = document.createElement('script');
script_tag.setAttribute("type", "text/javascript");
script_tag.setAttribute("src",
"https://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.4/jquery.min.js");
document.documentElement).appendChild(script_tag);
//Once loaded load other javascripts
if (this.readyState == 'complete' || this.readyState == 'loaded') {
scriptLoadHandler();
}
}
Following is my scriptLoadHandler function:
function scriptLoadHandler() {
// Restore $ and window.jQuery to their previous values and store the
// new jQuery in our local jQuery variable
jQuery = window.jQuery.noConflict(true);
// Call our main function
main();
}
Now, in the main method i'm trying to load Bootstrap js like this:
function main() {
console.log("undefined" == typeof jQuery);
var head = document.getElementsByTagName("head")[0];
var js = document.createElement("script");
js.type = "text/javascript";
js.src = "https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/js/bootstrap.min.js";
head.appendChild(js);
}
But it's still giving me above error even though the order in which they load is correct and when i check console log it gives me false which means jQuery is defined.

Check if JQuery is loaded before of bootstrap loading request. If JQuery is not already loaded bootstrap can not be loaded

//Load jquery here
You're not loading jQuery there.
You should either create a SCRIPT element in the DOM before this script with src your jQuery lib location, or load it dynamically after the line I've quoted (i.e. create the script tag, set the src to your jquery lib relative or absolute URL/URI, add the onloaded event handler to execute scriptLoadHandler and eventually append the new script to the DOM)
Easiest way is to load the script via a script TAG BEFORE the script you're using.
EDIT: after more information by OP, here is the solution:
check for the version of jQuery: if it's not the one you want, load it.
After you've loaded the jQuery version you need (or if it's already loaded), load Bootstrap.
JSFiddle: http://jsfiddle.net/1h6emjwu/2/
function loadScript(src, callback) {
var js = document.createElement('script');
js.src = src;
js.type = 'text/javascript';
if (typeof callback === 'function') {
js.addEventListener('load', callback);
}
document.body.appendChild(js);
}
var myScript = function () {
//alert(window.jQuery.fn.jquery);
alert($.fn.modal ? 'Bootstrap loaded' : 'Bootstrap not loaded');
}
if (window.jQuery === undefined || window.jQuery.fn.jquery !== '2.1.4') {
window.oldJQuery = window.jQuery; // so that you can return back whenever you want
loadScript('https://ajax.googleapis.com/ajax/libs/jquery/2.1.4/jquery.min.js', function () {
loadScript('https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/js/bootstrap.min.js', myScript);
});
} else {
loadScript('https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/js/bootstrap.min.js', myScript);
}

Replace DOM with javascript and run new scripts

I am trying to replace the whole DOM on page load to do a no-js fallback for a user created knockout page.
I have it replacing the DOM, but when I do the scripts included in the new document aren't running. I was wondering if theres any way of forcing them to run.
<!DOCTYPE html>
<html>
<head>
<title>Title1</title>
</head>
<body>
Hello world <!-- No JS enabled content -->
</body>
<script type="text/javascript">
var model = { 'template' : '\u003chtml\u003e\u003chead\u003e\u003ctitle\u003eTitle2\u003c/title\u003e\u003cscript type=\"text/javascript\"\u003ealert(\"test\");\u003c/script\u003e\u003c/head\u003e\u003cbody\u003eHello world2\u003c/body\u003e\u003c/html\u003e' };
document.documentElement.innerHTML = model.template;
</script>
</html>
template contains the following encoded
<html>
<head>
<title>aaa</title>
<script type='text/javascript'>alert('hello world');</script>
</head>
<body>
Hello world <!-- JS enabled content -->
</body>
</html>
how can I get the alert to run?

As you've discovered, the code in the script tags in the text you assign to innerHTML is not executed. Interestingly, though, on every browser I've tried, the script elements are created and placed in the DOM.
This means it's easy to write a function to run them, in order, and without using eval and its weird effect on scope:
function runScripts(element) {
var scripts;
// Get the scripts
scripts = element.getElementsByTagName("script");
// Run them in sequence (remember NodeLists are live)
continueLoading();
function continueLoading() {
var script, newscript;
// While we have a script to load...
while (scripts.length) {
// Get it and remove it from the DOM
script = scripts[0];
script.parentNode.removeChild(script);
// Create a replacement for it
newscript = document.createElement('script');
// External?
if (script.src) {
// Yes, we'll have to wait until it's loaded before continuing
newscript.onerror = continueLoadingOnError;
newscript.onload = continueLoadingOnLoad;
newscript.onreadystatechange = continueLoadingOnReady;
newscript.src = script.src;
}
else {
// No, we can do it right away
newscript.text = script.text;
}
// Start the script
document.documentElement.appendChild(newscript);
// If it's external, wait for callback
if (script.src) {
return;
}
}
// All scripts loaded
newscript = undefined;
// Callback on most browsers when a script is loaded
function continueLoadingOnLoad() {
// Defend against duplicate calls
if (this === newscript) {
continueLoading();
}
}
// Callback on most browsers when a script fails to load
function continueLoadingOnError() {
// Defend against duplicate calls
if (this === newscript) {
continueLoading();
}
}
// Callback on IE when a script's loading status changes
function continueLoadingOnReady() {
// Defend against duplicate calls and check whether the
// script is complete (complete = loaded or error)
if (this === newscript && this.readyState === "complete") {
continueLoading();
}
}
}
}
Naturally the scripts can't use document.write.
Note how we have to create a new script element. Just moving the existing one elsewhere in the document doesn't work, it's been marked by the browser as having been run (even though it wasn't).
The above will work for most people using innerHTML on an element somewhere in the body of the document, but it won't work for you, because you're actually doing this on the document.documentElement. That means the NodeList we get back from this line:
// Get the scripts
scripts = element.getElementsByTagName("script");
...will keep expanding as we add further scripts to the document.documentElement. So in your particular case, you have to turn it into an array first:
var list, scripts, index;
// Get the scripts
list = element.getElementsByTagName("script");
scripts = [];
for (index = 0; index < list.length; ++index) {
scripts[index] = list[index];
}
list = undefined;
...and later in continueLoading, you have to manually remove entries from the array:
// Get it and remove it from the DOM
script = scripts[0];
script.parentNode.removeChild(script);
scripts.splice(0, 1); // <== The new line
Here's a complete example for most people (not you), including the scripts doing things like function declarations (which would be messed up if we used eval): Live Copy | Live Source
<!DOCTYPE html>
<html>
<head>
<meta charset=utf-8 />
<title>Run Scripts</title>
</head>
<body>
<div id="target">Click me</div>
<script>
document.getElementById("target").onclick = function() {
display("Updating div");
this.innerHTML =
"Updated with script" +
"<div id='sub'>sub-div</div>" +
"<script src='http://ajax.googleapis.com/ajax/libs/jquery/1.10.1/jquery.min.js'></scr" + "ipt>" +
"<script>" +
"display('Script one run');" +
"function foo(msg) {" +
" display(msg); " +
"}" +
"</scr" + "ipt>" +
"<script>" +
"display('Script two run');" +
"foo('Function declared in script one successfully called from script two');" +
"$('#sub').html('updated via jquery');" +
"</scr" + "ipt>";
runScripts(this);
};
function runScripts(element) {
var scripts;
// Get the scripts
scripts = element.getElementsByTagName("script");
// Run them in sequence (remember NodeLists are live)
continueLoading();
function continueLoading() {
var script, newscript;
// While we have a script to load...
while (scripts.length) {
// Get it and remove it from the DOM
script = scripts[0];
script.parentNode.removeChild(script);
// Create a replacement for it
newscript = document.createElement('script');
// External?
if (script.src) {
// Yes, we'll have to wait until it's loaded before continuing
display("Loading " + script.src + "...");
newscript.onerror = continueLoadingOnError;
newscript.onload = continueLoadingOnLoad;
newscript.onreadystatechange = continueLoadingOnReady;
newscript.src = script.src;
}
else {
// No, we can do it right away
display("Loading inline script...");
newscript.text = script.text;
}
// Start the script
document.documentElement.appendChild(newscript);
// If it's external, wait for callback
if (script.src) {
return;
}
}
// All scripts loaded
newscript = undefined;
// Callback on most browsers when a script is loaded
function continueLoadingOnLoad() {
// Defend against duplicate calls
if (this === newscript) {
display("Load complete, next script");
continueLoading();
}
}
// Callback on most browsers when a script fails to load
function continueLoadingOnError() {
// Defend against duplicate calls
if (this === newscript) {
display("Load error, next script");
continueLoading();
}
}
// Callback on IE when a script's loading status changes
function continueLoadingOnReady() {
// Defend against duplicate calls and check whether the
// script is complete (complete = loaded or error)
if (this === newscript && this.readyState === "complete") {
display("Load ready state is complete, next script");
continueLoading();
}
}
}
}
function display(msg) {
var p = document.createElement('p');
p.innerHTML = String(msg);
document.body.appendChild(p);
}
</script>
</body>
</html>
And here's your fiddle updated to use the above where we turn the NodeList into an array:
HTML:
<body>
Hello world22
</body>
Script:
var model = {
'template': '\t\u003chtml\u003e\r\n\t\t\u003chead\u003e\r\n\t\t\t\u003ctitle\u003eaaa\u003c/title\u003e\r\n\t\t\t\u003cscript src=\"http://cdnjs.cloudflare.com/ajax/libs/jquery/1.10.1/jquery.min.js\"\u003e\u003c/script\u003e\r\n\t\t\t\u003cscript type=\u0027text/javascript\u0027\u003ealert($(\u0027body\u0027).html());\u003c/script\u003e\r\n\t\t\u003c/head\u003e\r\n\t\t\u003cbody\u003e\r\n\t\t\tHello world\r\n\t\t\u003c/body\u003e\r\n\t\u003c/html\u003e'
};
document.documentElement.innerHTML = model.template;
function runScripts(element) {
var list, scripts, index;
// Get the scripts
list = element.getElementsByTagName("script");
scripts = [];
for (index = 0; index < list.length; ++index) {
scripts[index] = list[index];
}
list = undefined;
// Run them in sequence
continueLoading();
function continueLoading() {
var script, newscript;
// While we have a script to load...
while (scripts.length) {
// Get it and remove it from the DOM
script = scripts[0];
script.parentNode.removeChild(script);
scripts.splice(0, 1);
// Create a replacement for it
newscript = document.createElement('script');
// External?
if (script.src) {
// Yes, we'll have to wait until it's loaded before continuing
newscript.onerror = continueLoadingOnError;
newscript.onload = continueLoadingOnLoad;
newscript.onreadystatechange = continueLoadingOnReady;
newscript.src = script.src;
} else {
// No, we can do it right away
newscript.text = script.text;
}
// Start the script
document.documentElement.appendChild(newscript);
// If it's external, wait
if (script.src) {
return;
}
}
// All scripts loaded
newscript = undefined;
// Callback on most browsers when a script is loaded
function continueLoadingOnLoad() {
// Defend against duplicate calls
if (this === newscript) {
continueLoading();
}
}
// Callback on most browsers when a script fails to load
function continueLoadingOnError() {
// Defend against duplicate calls
if (this === newscript) {
continueLoading();
}
}
// Callback on IE when a script's loading status changes
function continueLoadingOnReady() {
// Defend against duplicate calls and check whether the
// script is complete (complete = loaded or error)
if (this === newscript && this.readyState === "complete") {
continueLoading();
}
}
}
}
runScripts(document.documentElement);
This approach just occurred to me today when reading your question. I've never seen it used before, but it works in IE6, IE8, Chrome 26, Firefox 20, and Opera 12.15.

To force the scripts the run you can iterate over the script elements and run them using eval or more preferably using Function but it runs outside the scope of the script tag so you will not have access to local variables. (document.currentScript will be null):
document.querySelectorAll('script').forEach(script => {
if (!script.src)
new Function(script.text)()
else {
fetch(script.src).then(response => {
return response.text().then(text => {
new Function(text)()
});
})
}
})

Load external JavaScript files where A requires B being loaded asynchronously

I have a use case where I have a JS file that is lazy loaded. During development this JS file would be a combination of File A and File B. However in production it should load File A then File B for separation.
This works properly when adding them directly to the DOM with
for(int i =0; i < urls.length; i++) {
document.write("<script type='text/javascript' src='" + urls[i] + "'></script>");
}
Even if FileB loads before FileA, it doesn't get evaluated first.
My code is as follows
createScript: function(url, id) {
var m = this;
// flag as loaded
var myonload = function() {
Logger.debug(formatMessage(Library.RESOURCES["load.success"], [this.src, id]), "core");
this.library_loaded = true;
};
// log loading error
var myonerror = function() {
Logger.warn(formatMessage(Library.RESOURCES["load.failure"], [this.src, id]), "core");
};
//If currently being grabbed
// || m.currentAsyc[ids[i]+"/async"]
if (Library.findScript(url))
return;
var script = document.createElement("script");
script.type = "text/javascript";
script.library_loaded = false;
// mozilla
script.onload = myonload;
script.onerror = myonerror;
// ie
script.onreadystatechange = function() {
if (this.readyState == "complete" || this.readyState == "loaded") {
setTimeout(myonload.bindAsEventListener(this), 10);
this.onreadystatechange = null;
}
};
script.src = url;
m.head.appendChild(script);
},
This results in the DOM having
<script type="text/javascript" src="/path/to/FileA"></script>
<script type="text/javascript" src="/path/to/FileB"></script>
But when FileB loads faster then FileA it tries to evaluate itself first.
Is there any way to prevent this?
Further explanation
I am trying to implement a Sprockets like functionality into a legacy system.
When I would normally ask for '/dyn/path/to/FileA' it would have
//= require FileB at the top sending a respones of
document.write("<script type="text/javascript" src="/path/to/FileA"></script>");
document.write("<script type="text/javascript" src="/path/to/FileB"></script>");
This works great as it does the calls synchronously.
In this situation, I have made an AJAX call to see what files the dynamic FileA requires (those would be FileA and FileB). This returns saying that we need to request FileA and FileB. The problem is I need a call back to confirm when both of those files are actually loaded as I have a wait function for other areas that need this code as well. They are currently waiting just for the /dyn/path/to/FileA to complete loading, however we now need them to wait for FileA and FileB to complete their loading as well.

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.

We Keep Coding

JavaScript is the programming language of the Web.

Verify External Script Is Loaded - javascript

I found a quick tip before you start diving into code that might save a bit of time. Check devtools on the webpage and click on the network tab. The js scripts are shown if they are loaded as a 200 response from the server.

Related

How to recognize that one js file loaded?

Error:Bootstrap's JavaScript requires jQuery

Replace DOM with javascript and run new scripts

Load external JavaScript files where A requires B being loaded asynchronously

load scripts asynchronously

Categories

Resources