You might be familiar with the good old Jquery load fallback:
<script>window.jQuery || document.write('<script src="https://example.com/jquery.js"></script>')</script>
But I read here and there: don’t use document.write, is bad for your health, it does not work on Chrome (It’s working for me, Chrome 78).
So I’m trying to replace it, but I’m not able to find a solution that will load synchronously the new js file, before DOM loaded is triggered.
And what ends happening with a DOM manipulation alternative is that the browser consideres the DOM is loaded and all $(document).ready() fail with “$ is not defined”.
function Jqfallback() {
var j = document.createElement('script');
j.src = 'https://example.com/jquery.js';
document.getElementsByTagName('head')[0].appendChild(j);
}
(window.jQuery || Jqfallback() );
No matter where I put this script, or the new JS file, which in this case ('head')[0] is already before all other JS which are in the body, it loads it “asyncronically”.
Is there another option or I continue rocking document.write() in late 2019?
It takes a bit of time to load and parse JQuery. So use a (small) timeout after appending the script.
This snippet wraps conditional loading in a immediately executed anonymous function:
(myScripting => {
if (!window.$) {
let j = document.createElement('script');
j.src = '//code.jquery.com/jquery-3.4.1.slim.min.js';
document.querySelector('head').appendChild(j);
setTimeout( myScripting, 200 );
} else {
myScripting();
}
})(JqIsLoadedSoMyScriptingCanStart);
// put your main scripting in here
function JqIsLoadedSoMyScriptingCanStart() {
// extra check
if (!window.$) {
alert("Sorry, JQuery is not loaded, can't continue");
return;
}
console.log("JQuery in place?");
console.log($("head script")[1]);
}
<script src="cantLoadThis"></script>
Place the code that uses jQuery in the onload() function.
var jQuery1 = document.createElement('script');
jQuery1.src = "https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js";
jQuery1.onload = function () {
var $ = window.jQuery;
$.when(
$.getScript("https://someOtherScript.js"), //if you need
$.Deferred(function (deferred) {
$(deferred.resolve);
})
).done(function () {
console.log("all scripts loaded!!");
doNextTask(); //some other code which uses jQuery
});
};
Append jQuery to your document in onreadystatechange
document.onreadystatechange = function () {
if (document.readyState == "complete") {
// document is ready.
document.head.appendChild(jQuery1);
}
}
Related
I need to add jquery and then another script that relies on jquery.
I then need to have code that uses both assets but my problem is that i don't want my code to run until i know that both assets are loaded.
I think the process would be to load jquery and then wait until jquery is loaded by waiting for window.onload, then load the jquery plugin, then detect that the plugin has loaded, then load my own code that uses functions from the jquery plugin.
code so far:
// load jquery if it is not allready loaded and put it into no conflict mode so the $ is available for other librarys that might be allready on the page.
if(!window.jQuery) {
var script = document.createElement('script');
script.type = "text/javascript";
script.src = "http://ajax.googleapis.com/ajax/libs/jquery/1.8.1/jquery.min.js";
document.getElementsByTagName('head')[0].appendChild(script);
jQuery.noConflict(); // stop jquery eating the $
console.log("added jquery");
}
window.onload = function(e) {
// we know that jquery should be available now as the window has loaded
if ( !jQuery.isFunction(jQuery.fn.serializeObject) ) { // use jquery to ask if the plugins function is allready on the page (don't do this if the website already had the plugin)
// website didn't have the plugin so add it to the page.
var script = document.createElement('script');
script.type = "text/javascript";
script.src = "https://cdnjs.cloudflare.com/ajax/libs/jquery-serialize-object/2.5.0/jquery.serialize-object.min.js";
document.getElementsByTagName('head')[0].appendChild(script);
}
if ( !jQuery.isFunction(jQuery.fn.serializeObject) ) {
// console.log("serializeObject is undefined");
// its going to be undefined here because Its still loading in the script
} else {
// console.log("we have serializeObject");
}
// I now dont know when to call my code that uses .serializeObject() because it could still be loading
// my code
var form_data_object = jQuery('form#mc-embedded-subscribe-form').serializeObject();
};
You have to do like
Include
<script type="text/javascript" id="AssetJS"></script>
Script
$("#AssetJS").attr("src", "Asset.js");
$("#AssetJS").load(function () {
//after loaded jquery asset do your code here
})
OK i managed to find another way that is working for my specific needs so I am answering my own question.
Using this function from http://www.sitepoint.com/dynamically-load-jquery-library-javascript/
function loadScript(url, callback) {
var script = document.createElement("script")
script.type = "text/javascript";
if (script.readyState) { //IE
script.onreadystatechange = function () {
if (script.readyState == "loaded" || script.readyState == "complete") {
script.onreadystatechange = null;
callback();
}
};
} else { //Others
script.onload = function () {
callback();
};
}
script.src = url;
document.getElementsByTagName("head")[0].appendChild(script);
}
and usage in my case:
if(!window.jQuery) {
loadScript("https://ajax.googleapis.com/ajax/libs/jquery/1.8.1/jquery.min.js", function () {
jQuery.noConflict(); // stop jquery eating the $
console.log('jquery loaded');
if ( !jQuery.isFunction(jQuery.fn.serializeObject) ) { // use jquery to ask if the plugins function is already on the page
loadScript("https://cdnjs.cloudflare.com/ajax/libs/jquery-serialize-object/2.5.0/jquery.serialize-object.min.js", function () {
console.log('serialize loaded');
SURGE_start(); // both scrips where not on the website but have now been added so lets run my code now.
});
}
});
} else {
if ( !jQuery.isFunction(jQuery.fn.serializeObject) ) { // use jquery to ask if the plugins function is already on the page
loadScript("https://cdnjs.cloudflare.com/ajax/libs/jquery-serialize-object/2.5.0/jquery.serialize-object.min.js", function () {
console.log('serialize loaded');
SURGE_start(); // jquery was on the web page but the plugin was not included. now we have both scripts lets run my code.
});
} else {
SURGE_start(); // web page already had both scripts so just run my code.
}
}
An easy way is using headjs. It's working fine on several projects.
The following works but I need to distribute it to clients that may be uncomfortable of pasting all this script into their home page. Just wondering if it can be simplified? I need to load Jquery 1.71, then the UI and then my own script and then call the function in my own script. Even minimized its rather long.
Hope some javascript guru can help. Thanks!
var head = document.getElementsByTagName('head')[0];
var script = document.createElement('script');
script.src = 'https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js';
script.type = 'text/javascript';
head.appendChild(script);
if (script.onreadystatechange) script.onreadystatechange = function () {
if (script.readyState == "complete" || script.readyState == "loaded") {
script.onreadystatechange = false;
//alert("complete");
load_script();
}
} else {
script.onload = function () {
//alert("complete");
load_script();
}
}
//setup array of scripts and an index to keep track of where we are in the process
var scripts = ['script/jquery-ui-1.8.7.custom.min.js', 'script/wfo171.js'],
index = 0;
//setup a function that loads a single script
function load_script() {
//make sure the current index is still a part of the array
if (index < scripts.length) {
//get the script at the current index
$.getScript('http://mydomainn.com/script/' + scripts[index], function () {
//once the script is loaded, increase the index and attempt to load the next script
//alert('Loaded: ' + scripts[index] + "," + index);
if (index != 0) {
LoadEdge();
}
index++;
load_script();
});
}
}
function LoadEdge() {
Edge('f08430fa2a');
}
As soon as you have jQuery you can use its power:
$.when.apply($, $.map(scripts, $.getScript)).then(LoadEdge);
This relies on its deferred functionality - each URL is replaced with a getScript deferred (this will fetch the script), and these deferreds are then passed to $.when so that you can add a callback using .then to be called when all scripts have finished loaded.
Why don;t you just use an onload event to make sure everything is loaded before trying to execute?
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script>
<script src="http://mydomainn.com/script/jquery-ui-1.8.7.custom.min.js"></script>
<script src="http://mydomainn.com/script/wfo171.js"></script>
<script>
$(function() { // this executes when the page is ready
Edge('f08430fa2a');
});
</script>
(check the paths on the scripts, you seem to be loading from /script/script, wasn't sure if that was correct so I removed it.
UPDATE:
I have the following code:
<script type="text/javascript">
function addScript(url) {
var script = document.createElement('script');
script.src = url;
document.getElementsByTagName('head')[0].appendChild(script);
}
addScript('http://google.com/google-maps.js');
addScript('http://jquery.com/jquery.js');
...
// run code below this point once both google-maps.js & jquery.js has been downloaded and excuted
</script>
How can I prevent code from executing until all required JS have been downloaded and executed? In my example above, those required files being google-maps.js and jquery.js.
You can use the onload event of the script element for most browsers, and use a callback argument:
Edit: You can't really stop the execution of the code when you load scripts in this way (and making synchronous Ajax requests is a bad idea most of the times).
But you can chain callbacks, so if you have some code that depends on both, Two.js and Three.js, you can chain the loading actions, for example:
loadScript('http://example.com/Two.js', function () {
// Two.js is already loaded here, get Three.js...
loadScript('http://example.com/Three.js', function () {
// Both, Two.js and Three.js loaded...
// you can place dependent code here...
});
});
Implementation:
function loadScript(url, callback) {
var head = document.getElementsByTagName("head")[0],
script = document.createElement("script"),
done = false;
script.src = url;
// Attach event handlers for all browsers
script.onload = script.onreadystatechange = function(){
if ( !done && (!this.readyState || // IE stuff...
this.readyState == "loaded" || this.readyState == "complete") ) {
done = true;
callback(); // execute callback function
// Prevent memory leaks in IE
script.onload = script.onreadystatechange = null;
head.removeChild( script );
}
};
head.appendChild(script);
}
For IE, the onreadystatechange event has to be bound.
I just read CMS's answer, and decided that from his "most browsers" comment, I might have a crack at getting it work for ones that do not have this functionality natively.
Basically, it's an interval that polls for a variable.
var poll = window.setInterval(function() {
if (typeof myVar !== 'undefined') {
clearInterval(poll);
doSomething();
};
}, 100);
I'm developing a javascript widget that depends on jQuery. The widget may or may not be loaded onto a page that already has jQuery loaded. There are many problems that come up in this case...
If the web page does not have jQuery, I must load my own jQuery. There seems to be a delicate timing issue when doing this, however. For example, if my widget loads and executes before jQuery is finished loading and executing, I get a jQuery is not defined error.
If the web page does have jQuery, I can usually work with it. If the jQuery version is old, however, I would like to load my own. If I do load my own, however, I need to do it in such a way as to not stomp on their $ variable. If I set jQuery.noConflict() and any of their scripts depend on $, then I have just broken their page.
If the web page uses another javascript library (e.g. prototype), I needed to be sensitive of prototype's $ variable also.
Because of all of the above, it is seeming easier to not depend on jQuery. But before I go down that road, which will involve mostly rewriting my widget code, I wanted to ask for advice first.
The basic skeleton of my code, including the timing bug and sometimes $ bugs, follows:
<script type="text/javascript" charset="utf-8">
// <![CDATA
if (typeof jQuery === 'undefined') {
var head = document.getElementsByTagName('head')[0];
var script = document.createElement('script');
script.type = 'text/javascript';
script.src = '{{ URL }}/jquery.js';
head.appendChild(script);
}
// ]]>
</script>
<script type="text/javascript" src="{{ URL }}/widget.js"></script>
My widget has the following structure:
(function($) {
var mywidget = {
init: function() {
...
}
};
$(document).ready(function() {
mywidget.init();
});
})(jQuery);
If there are any pointers or resources for achieving a widget that can work in all the mentioned environments, they would be greatly appreciated.
After reviewing some answers and pointers, and finding some helpful jQuery hackers, I ended up with something like the following:
(function(window, document, version, callback) {
var j, d;
var loaded = false;
if (!(j = window.jQuery) || version > j.fn.jquery || callback(j, loaded)) {
var script = document.createElement("script");
script.type = "text/javascript";
script.src = "/media/jquery.js";
script.onload = script.onreadystatechange = function() {
if (!loaded && (!(d = this.readyState) || d == "loaded" || d == "complete")) {
callback((j = window.jQuery).noConflict(1), loaded = true);
j(script).remove();
}
};
(document.getElementsByTagName("head")[0] || document.documentElement).appendChild(script);
}
})(window, document, "1.3", function($, jquery_loaded) {
// Widget code here
});
This will load jQuery if it's not already loaded and encapsulates it in the callback so it doesn't conflict with a pre-existing jQuery on the page. It also checks that a minimum version is available or else loads a known version -- in this case, v1.3. It sends a boolean value to the callback (my widget) on whether or not jQuery was loaded in case there are any triggers needed to be made. And only after jQuery is loaded does it call my widget, passing jQuery into it.
See How to build a web widget (using jQuery) by Alex Marandon.
(function() {
// Localize jQuery variable
var jQuery;
/******** Load jQuery if not present *********/
if (window.jQuery === undefined || window.jQuery.fn.jquery !== '1.4.2') {
var script_tag = document.createElement('script');
script_tag.setAttribute("type","text/javascript");
script_tag.setAttribute("src",
"http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js");
if (script_tag.readyState) {
script_tag.onreadystatechange = function () { // For old versions of IE
if (this.readyState == 'complete' || this.readyState == 'loaded') {
scriptLoadHandler();
}
};
} else { // Other browsers
script_tag.onload = scriptLoadHandler;
}
// Try to find the head, otherwise default to the documentElement
(document.getElementsByTagName("head")[0] || document.documentElement).appendChild(script_tag);
} else {
// The jQuery version on the window is the one we want to use
jQuery = window.jQuery;
main();
}
/******** Called once jQuery has loaded ******/
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();
}
/******** Our main function ********/
function main() {
jQuery(document).ready(function($) {
// We can use jQuery 1.4.2 here
});
}
})(); // We call our anonymous function immediately
What if you also want to use some jQuery plugins? Is it safe to make yourself a single file with the minified versions of the plugins, and also load those, as below? (Loaded from S3, in this particular example.)
(function(window, document, version, callback) {
var j, d;
var loaded = false;
if (!(j = window.jQuery) || version > j.fn.jquery || callback(j, loaded)) {
var script = document.createElement("script");
script.type = "text/javascript";
script.src = "http://ajax.googleapis.com/ajax/libs/jquery/1.5.2/jquery.min.js";
script.onload = script.onreadystatechange = function() {
if (!loaded && (!(d = this.readyState) || d == "loaded" || d == "complete")) {
window.jQuery.getScript('http://mydomain.s3.amazonaws.com/assets/jquery-plugins.js', function() {
callback((j = window.jQuery).noConflict(1), loaded = true);
j(script).remove();
});
}
};
document.documentElement.childNodes[0].appendChild(script)
}
})(window, document, "1.5.2", function($, jquery_loaded) {
// widget code goes here
});
SEE Can I use multiple versions of jQuery on the same page?
Can you use document.write() to optionally add the jQuery script to the page? That should force jQuery to load synchronously. Try this:
<script type="text/javascript" charset="utf-8">
// <![CDATA
if (typeof jQuery === 'undefined') {
document.write('<script src="{{ URL }}/jquery.js"><' + '/script>');
}
// ]]>
</script>
<script type="text/javascript" src="{{ URL }}/widget.js"></script>
If you want to do the jQuery check inside your widget script then I believe the following works cross-browser:
(function() {
function your_call($) {
// your widget code goes here
}
if (typeof jQuery !== 'undefined') your_call(jQuery);
else {
var head = document.getElementsByTagName('head')[0];
var script = document.createElement('script');
script.type = 'text/javascript';
script.src = '{{ URL }}/jquery.js';
var onload = function() {
if (!script.readyState || script.readyState === "complete") your_call(jQuery);
}
if ("onreadystatechange" in script) script.onreadystatechange = onload;
else script.onload = onload;
head.appendChild(script);
}
})()
I know this is an old topic... but i got something faster that your hack.
Try in your widget
"init": function()
that will fix the trouble
I would download the jQuery source and modify the jQuery object to another (jQueryCustom).
And then find the instance that sets the $ symbol as a jQuery object and comment that routine.
I don't know how easy or difficult could that be, but I'd sure give it a try.
(Also, check your second option, as it is not bad, the site where the widget will be executing, might have a jQuery version older than the one you need).
EDIT: I just checked the source. You just have to replace jQuery with another string (jQcustom for example). Then, try commenting this line:
_$ = window.$
And you make reference to the custom jQuery like this:
jQcustom("#id").attr(...)
I've got a bookmarklet which loads jQuery and some other js libraries.
How do I:
Wait until the javascript library I'm using is available/loaded. If I try to use the script before it has finished loading, like using the $ function with jQuery before it's loaded, an undefined exception is thrown.
Insure that the bookmarklet I load won't be cached (without using a server header, or obviously, being that this is a javascript file: a metatag)
Is anyone aware if onload for dynamically added javascript works in IE? (to contradict this post)
What's the simplest solution, cleanest resolution to these issues?
It depends on how you are actually loading jQuery. If you are appending a script element to the page, you can use the same technique that jQuery uses to dynamically load a script.
EDIT: I did my homework and actually extracted a loadScript function from the jQuery code to use in your bookmarklet. It might actually be useful to many (including me).
function loadScript(url, callback)
{
var head = document.getElementsByTagName("head")[0];
var script = document.createElement("script");
script.src = url;
// Attach handlers for all browsers
var done = false;
script.onload = script.onreadystatechange = function()
{
if( !done && ( !this.readyState
|| this.readyState == "loaded"
|| this.readyState == "complete") )
{
done = true;
// Continue your code
callback();
// Handle memory leak in IE
script.onload = script.onreadystatechange = null;
head.removeChild( script );
}
};
head.appendChild(script);
}
// Usage:
// This code loads jQuery and executes some code when jQuery is loaded
loadScript("https://code.jquery.com/jquery-latest.js", function()
{
$('my_element').hide();
});
To answer your first question: Javascript is interpreted sequentially, so any following bookmarklet code will not execute until the library is loaded (assuming the library was interpreted successfully - no syntax errors).
To prevent the files from being cached, you can append a meaningless query string...
url = 'jquery.js?x=' + new Date().getTime();
I've paid an attention that in Chrome the order of scripts that are loaded is undetermined, when using #Vincent Robert's technique. In this case a little modification helps:
(function() {
var callback = function() {
// Do you work
};
// check for our library existence
if (typeof (MyLib) == 'undefined') {
var sources = [
'http://ajax.cdnjs.com/ajax/libs/json2/20110223/json2.js',
'https://ajax.googleapis.com/ajax/libs/jquery/1.6.1/jquery.min.js',
'https://ajax.googleapis.com/ajax/libs/jqueryui/1.8.13/jquery-ui.min.js',
'http://myhost.com/javascripts/mylib.min.js'];
var loadNextScript = function() {
if (sources.length > 0) {
var script = document.createElement('script');
script.src = sources.shift();
document.body.appendChild(script);
var done = false;
script.onload = script.onreadystatechange = function() {
if (!done
&& (!this.readyState || this.readyState == "loaded" || this.readyState == "complete")) {
done = true;
// Handle memory leak in IE
script.onload = script.onreadystatechange = null;
loadNextScript();
}
}
} else {
callback();
}
}
loadNextScript();
} else {
callback();
}
})();
I got a little closer with this, but not completely. It would be nice to have a discrete, example of a bookmarklet that demonstrated how to avoided caching.