What would be a good way to attempt to load the hosted jQuery at Google (or other Google hosted libs), but load my copy of jQuery if the Google attempt fails?
I'm not saying Google is flaky. There are cases where the Google copy is blocked (apparently in Iran, for instance).
Would I set up a timer and check for the jQuery object?
What would be the danger of both copies coming through?
Not really looking for answers like "just use the Google one" or "just use your own." I understand those arguments. I also understand that the user is likely to have the Google version cached. I'm thinking about fallbacks for the cloud in general.
Edit: This part added...
Since Google suggests using google.load to load the ajax libraries, and it performs a callback when done, I'm wondering if that's the key to serializing this problem.
I know it sounds a bit crazy. I'm just trying to figure out if it can be done in a reliable way or not.
Update: jQuery now hosted on Microsoft's CDN.
http://www.asp.net/ajax/cdn/
You can achieve it like this:
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.2.6/jquery.min.js"></script>
<script>
window.jQuery || document.write('<script src="/path/to/your/jquery"><\/script>');
</script>
This should be in your page's <head> and any jQuery ready event handlers should be in the <body> to avoid errors (although it's not fool-proof!).
One more reason to not use Google-hosted jQuery is that in some countries, Google's domain name is banned.
The easiest and cleanest way to do this by far:
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
<script>window.jQuery || document.write('<script src="path/to/your/jquery"><\/script>')</script>
This seems to work for me:
<html>
<head>
<script type="text/javascript" src="http://www.google.com/jsapi"></script>
<script type="text/javascript">
// has the google object loaded?
if (window.google && window.google.load) {
google.load("jquery", "1.3.2");
} else {
document.write('<script type="text/javascript" src="http://joecrawford.com/jquery-1.3.2.min.js"><\/script>');
}
window.onload = function() {
$('#test').css({'border':'2px solid #f00'});
};
</script>
</head>
<body>
<p id="test">hello jQuery</p>
</body>
</html>
The way it works is to use the google object that calling http://www.google.com/jsapi loads onto the window object. If that object is not present, we are assuming that access to Google is failing. If that is the case, we load a local copy using document.write. (I'm using my own server in this case, please use your own for testing this).
I also test for the presence of window.google.load - I could also do a typeof check to see that things are objects or functions as appropriate. But I think this does the trick.
Here's just the loading logic, since code highlighting seems to fail since I posted the whole HTML page I was testing:
if (window.google && window.google.load) {
google.load("jquery", "1.3.2");
} else {
document.write('<script type="text/javascript" src="http://joecrawford.com/jquery-1.3.2.min.js"><\/script>');
}
Though I must say, I'm not sure that if this is a concern for your site visitors you should be fiddling with the Google AJAX Libraries API at all.
Fun fact: I tried initially to use a try..catch block for this in various versions but could not find a combination that was as clean as this. I'd be interested to see other implementations of this idea, purely as an exercise.
If you have modernizr.js embedded on your site, you can use the built-in yepnope.js to load your scripts asynchronously - among others jQuery (with fallback).
Modernizr.load([{
load : '//ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js'
},{
test : window.jQuery,
nope : 'path/to/local/jquery-1.7.2.min.js',
both : ['myscript.js', 'another-script.js'],
complete : function () {
MyApp.init();
}
}]);
This loads jQuery from the Google-cdn. Afterwards it's checked, if jQuery was loaded successfully. If not ("nope"), the local version is loaded. Also your personal scripts are loaded - the "both" indicates, that the load-process is iniated independently from the result of the test.
When all load-processes are complete, a function is executed, in the case 'MyApp.init'.
I personally prefer this way of asynchronous script loading. And as I rely on the feature-tests provided by modernizr when building a site, I have it embedded on the site anyway. So there's actually no overhead.
There are some great solutions here, but I'll like to take it one step further regarding the local file.
In a scenario when Google does fail, it should load a local source but maybe a physical file on the server isn't necessarily the best option. I bring this up because I'm currently implementing the same solution, only I want to fall back to a local file that gets generated by a data source.
My reasons for this is that I want to have some piece of mind when it comes to keeping track of what I load from Google vs. what I have on the local server. If I want to change versions, I'll want to keep my local copy synced with what I'm trying to load from Google. In an environment where there are many developers, I think the best approach would be to automate this process so that all one would have to do is change a version number in a configuration file.
Here's my proposed solution that should work in theory:
In an application configuration file, I'll store 3 things: absolute URL for the library, the URL for the JavaScript API, and the version number
Write a class which gets the file contents of the library itself (gets the URL from app config), stores it in my datasource with the name and version number
Write a handler which pulls my local file out of the db and caches the file until the version number changes.
If it does change (in my app config), my class will pull the file contents based on the version number, save it as a new record in my datasource, then the handler will kick in and serve up the new version.
In theory, if my code is written properly, all I would need to do is change the version number in my app config then viola! You have a fallback solution which is automated, and you don't have to maintain physical files on your server.
What does everyone think? Maybe this is overkill, but it could be an elegant method of maintaining your AJAX libraries.
Acorn
if (typeof jQuery == 'undefined') {
// or if ( ! window.jQuery)
// or if ( ! 'jQuery' in window)
// or if ( ! window.hasOwnProperty('jQuery'))
var script = document.createElement('script');
script.type = 'text/javascript';
script.src = '/libs/jquery.js';
var scriptHook = document.getElementsByTagName('script')[0];
scriptHook.parentNode.insertBefore(script, scriptHook);
}
After you attempt to include Google's copy from the CDN.
In HTML5, you don't need to set the type attribute.
You can also use...
window.jQuery || document.write('<script src="/libs/jquery.js"><\/script>');
You might want to use your local file as a last resort.
Seems as of now jQuery's own CDN does not support https. If it did you then might want to load from there first.
So here's the sequence:
Google CDN =>
Microsoft CDN =>
Your local copy.
<!-- load jQuery from Google's CDN -->
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<!-- fallback to Microsoft's Ajax CDN -->
<script> window.jQuery || document.write('<script src="//ajax.aspnetcdn.com/ajax/jQuery/jquery-1.8.3.min.js">\x3C/script>')</script>
<!-- fallback to local file -->
<script> window.jQuery || document.write('<script src="Assets/jquery-1.8.3.min.js">\x3C/script>')</script>
Conditionally load latest/legacy jQuery version and fallback:
<!--[if lt IE 9]>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
<script>window.jQuery || document.write('<script src="/public/vendor/jquery-legacy/dist/jquery.min.js">\x3C/script>')</script>
<![endif]-->
<!--[if gte IE 9]><!-->
<script src="//ajax.googleapis.com/ajax/libs/jquery/2.1.4/jquery.min.js"></script>
<script>window.jQuery || document.write('<script src="/public/vendor/jquery/dist/jquery.min.js">\x3C/script>')</script>
<!--<![endif]-->
Step 1: Did jQuery fail to load? (check jQuery variable)
How to check a not-defined variable in JavaScript
Step 2: Dynamically import (the backup) javascript file
How do I include a JavaScript file in another JavaScript file?
Because of the Google's banning problem I prefer to use Microsoft's cdn
http://www.asp.net/ajaxlibrary/cdn.ashx
For those people using ASP.NET MVC 5, add this code in your BundleConfig.cs to enable the CDN for jquery:
bundles.UseCdn = true;
Bundle jqueryBundle = new ScriptBundle("~/bundles/jquery", "//ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js").Include("~/Scripts/jquery-{version}.js");
jqueryBundle.CdnFallbackExpression = "window.jQuery";
bundles.Add(jqueryBundle);
UPDATE:
This answer turned out to be wrong. Please see the comments for the real explanation.
Most of you question has been answered, but as for the final part:
What would be the danger of both copies coming through?
None really. You'd waste bandwidth, might add some milliseconds downloading a second useless copy, but there's not actual harm if they both come through. You should, of course, avoid this using the techniques mentioned above.
I made a Gist that should dynamically load jQuery if it isn't already loaded, and if the source fails, it proceeds onto fallbacks (stitched together from many answers): https://gist.github.com/tigerhawkvok/9673154
Please note I plan to keep the Gist updated but not this answer, for what it's worth!
/* See https://gist.github.com/tigerhawkvok/9673154 for the latest version */
function cascadeJQLoad(i) { // Use alternate CDNs where appropriate to load jQuery
if (typeof(i) != "number") i = 0;
// the actual paths to your jQuery CDNs
var jq_paths = [
"ajax.googleapis.com/ajax/libs/jquery/2.1.0/jquery.min.js",
"ajax.aspnetcdn.com/ajax/jQuery/jquery-2.1.0.min.js"
];
// Paths to your libraries that require jQuery
var dependent_libraries = [
"js/c.js"
];
if (window.jQuery === undefined && i < jq_paths.length) {
i++;
loadJQ(jq_paths[i], i, dependent_libraries);
}
if (window.jQuery === undefined && i == jq_paths.length) {
// jQuery failed to load
// Insert your handler here
}
}
/***
* You shouldn't have to modify anything below here
***/
function loadJQ(jq_path, i, libs) { //load jQuery if it isn't already
if (typeof(jq_path) == "undefined") return false;
if (typeof(i) != "number") i = 1;
var loadNextJQ = function() {
var src = 'https:' == location.protocol ? 'https' : 'http';
var script_url = src + '://' + jq_path;
loadJS(script_url, function() {
if (window.jQuery === undefined) cascadeJQLoad(i);
});
}
window.onload = function() {
if (window.jQuery === undefined) loadNextJQ();
else {
// Load libraries that rely on jQuery
if (typeof(libs) == "object") {
$.each(libs, function() {
loadJS(this.toString());
});
}
}
}
if (i > 0) loadNextJQ();
}
function loadJS(src, callback) {
var s = document.createElement('script');
s.src = src;
s.async = true;
s.onreadystatechange = s.onload = function() {
var state = s.readyState;
try {
if (!callback.done && (!state || /loaded|complete/.test(state))) {
callback.done = true;
callback();
}
} catch (e) {
// do nothing, no callback function passed
}
};
s.onerror = function() {
try {
if (!callback.done) {
callback.done = true;
callback();
}
} catch (e) {
// do nothing, no callback function passed
}
}
document.getElementsByTagName('head')[0].appendChild(s);
}
/*
* The part that actually calls above
*/
if (window.readyState) { //older microsoft browsers
window.onreadystatechange = function() {
if (this.readyState == 'complete' || this.readyState == 'loaded') {
cascadeJQLoad();
}
}
} else { //modern browsers
cascadeJQLoad();
}
Google Hosted jQuery
If you care about older browsers, primarily versions of IE prior to IE9, this is the most widely compatible jQuery version
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
If you don’t care about oldIE, this one is smaller and faster:
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.4/jquery.min.js"></script>
Backup/Fallback Plan!
Either way, you should use a fallback to local just in case the Google CDN fails (unlikely) or is blocked in a location that your users access your site from (slightly more likely), like Iran or sometimes China.
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
<script>if (!window.jQuery) { document.write('<script src="/path/to/your/jquery"><\/script>'); }
</script>
Reference: http://websitespeedoptimizations.com/ContentDeliveryNetworkPost.aspx
I consider that should escape the last < to \x3C in string. When the browser sees , it considers this to be the end of the script block (since the HTML parser has no idea about JavaScript, it can't distinguish between something that just appears in a string, and something that's actually meant to end the script element). So appearing literally in JavaScript that's inside an HTML page will (in the best case) cause errors, and (in the worst case) be a huge security hole.
<script src="https://ajax.aspnetcdn.com/ajax/jquery/jquery-2.0.0.min.js"></script>
<script>window.jQuery || document.write('<script src="js/jquery-2.0.0.min.js">\x3C/script>')</script>
if (typeof jQuery == 'undefined')) { ...
Or
if(!window.jQuery){
Will not works if cdn version not loaded, because browser will run through this condition and during it still downloading the rest of javascripts which needs jQuery and it returns error. Solution was to load scripts through that condition.
<script src="http://WRONGPATH.code.jquery.com/jquery-1.4.2.min.js" type="text/javascript"></script><!-- WRONGPATH for test-->
<script type="text/javascript">
function loadCDN_or_local(){
if(!window.jQuery){//jQuery not loaded, take a local copy of jQuery and then my scripts
var scripts=['local_copy_jquery.js','my_javascripts.js'];
for(var i=0;i<scripts.length;i++){
scri=document.getElementsByTagName('head')[0].appendChild(document.createElement('script'));
scri.type='text/javascript';
scri.src=scripts[i];
}
}
else{// jQuery loaded can load my scripts
var s=document.getElementsByTagName('head')[0].appendChild(document.createElement('script'));
s.type='text/javascript';
s.src='my_javascripts.js';
}
}
window.onload=function(){loadCDN_or_local();};
</script>
Almost all public CDNs are pretty reliably. However, if you are worried about blocked google domain, then you can simply fallback to an alternative jQuery CDN. However, in such a case, you may prefer to do it opposite way and use some other CDN as your preferred option and fallback to Google CDN to avoid failed requests and waiting time:
<script src="https://pagecdn.io/lib/jquery/3.2.1/jquery.min.js"></script>
<script>
window.jQuery || document.write('<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"><\/script>');
</script>
Using Razor syntax in ASP.NET, this code provides fallback support and works with a virtual root:
#{var jQueryPath = Url.Content("~/Scripts/jquery-1.7.1.min.js");}
<script type="text/javascript">
if (typeof jQuery == 'undefined')
document.write(unescape("%3Cscript src='#jQueryPath' type='text/javascript'%3E%3C/script%3E"));
</script>
Or make a helper (helper overview):
#helper CdnScript(string script, string cdnPath, string test) {
#Html.Raw("<script src=\"http://ajax.aspnetcdn.com/" + cdnPath + "/" + script + "\" type=\"text/javascript\"></script>" +
"<script type=\"text/javascript\">" + test + " || document.write(unescape(\"%3Cscript src='" + Url.Content("~/Scripts/" + script) + "' type='text/javascript'%3E%3C/script%3E\"));</script>")
}
and use it like this:
#CdnScript("jquery-1.7.1.min.js", "ajax/jQuery", "window.jQuery")
#CdnScript("jquery.validate.min.js", "ajax/jquery.validate/1.9", "jQuery.fn.validate")
Although writing document.write("<script></script>") seems easier for jQuery backoff, Chrome gives validation error on that case. So I prefer breaking "script" word. So it becomes safer like above.
<script src="http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.11.1.min.js"></script>
<script>if (typeof jQuery === "undefined") {
window.jqFallback = true;
document.write("<scr"+"ipt src='http://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.1/jquery.min.js'></scr"+"ipt>");
} </script>
For long term issues, it would be better to log JQuery fallbacks. In the code above, if first CDN is not available JQuery is loaded from another CDN. But you could want to know that erroneous CDN and remove it permanently. (this case is very exceptional case) Also it is better to log fallback issues. So you can send erroneous cases with AJAX. Because of JQuery isn't defined, you should use vanilla javascript for AJAX request.
<script type="text/javascript">
if (typeof jQuery === 'undefined' || window.jqFallback == true) {
// XMLHttpRequest for IE7+, Firefox, Chrome, Opera, Safari
// ActiveXObject for IE6, IE5
var xmlhttp = window.XMLHttpRequest ? new XMLHttpRequest() : new ActiveXObject("Microsoft.XMLHTTP");
var url = window.jqFallback == true ? "/yourUrl/" : "/yourUrl2/";
xmlhttp.open("POST", url, true);
xmlhttp.send();
}
</script>
The inability to load the resource from an external data store beyond your control is difficult. Looking for missing functions is totally fallacious as a means to avoid suffering a timeout, as described herein:
http://www.tech-101.com/support/topic/4499-issues-using-a-cdn/
Yet another fallback that replaces ajax.googleapis.com with cdnjs.cloudflare.com:
(function (doc, $)
{
'use strict';
if (typeof $ === 'undefined')
{
var script = doc.querySelector('script[src*="jquery.min.js"]'),
src = script.src.replace('ajax.googleapis.com', 'cdnjs.cloudflare.com');
script.parentNode.removeChild(script);
doc.write('<script src="' + src + '"></script>');
}
})(document, window.jQuery || window.Zepto);
You can stick to a jQuery version by specifying it in the string
Perfect for Asset Management that doesn't work with HTML snips
Tested in the wild - works perfect for users from China
You can use code like:
<script type="text/javascript" src="http://code.jquery.com/jquery-latest.min.js"></script>
<script>window.jQuery || document.write('<script type="text/javascript" src="./scripts/jquery.min.js">\x3C/script>')</script>
But also there are libraries you can use to setup several possible fallbacks for your scripts and optimize the loading process:
basket.js
RequireJS
yepnope
Examples:
basket.js
I think the best variant for now. Will cach your script in the localStorage, that will speed up next loadings. The simplest call:
basket.require({ url: '/path/to/jquery.js' });
This will return a promise and you can do next call on error, or load dependencies on success:
basket
.require({ url: '/path/to/jquery.js' })
.then(function () {
// Success
}, function (error) {
// There was an error fetching the script
// Try to load jquery from the next cdn
});
RequireJS
requirejs.config({
enforceDefine: true,
paths: {
jquery: [
'//ajax.aspnetcdn.com/ajax/jquery/jquery-2.0.0.min',
//If the CDN location fails, load from this location
'js/jquery-2.0.0.min'
]
}
});
//Later
require(['jquery'], function ($) {
});
yepnope
yepnope([{
load: 'http://ajax.aspnetcdn.com/ajax/jquery/jquery-2.0.0.min.js',
complete: function () {
if (!window.jQuery) {
yepnope('js/jquery-2.0.0.min.js');
}
}
}]);
You should never need to use a personal copy. Here is my full belt and braces script.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8"/>
<title>jQuery</title>
<!-- EMBED JQUERY USING GOOGLE APIs -->
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/3.6.0/jquery.min.js"></script>
<!-- IF THAT FAILS EMBED JQUERY USING CLOUDFLARE CDN -->
<script type="text/javascript">
window.jQuery || document.write('<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.6.0/jquery.min.js"><\/script>');
</script>
<!-- IF THAT FAILS ************* HOW??? *********** EMBED JQUERY FROM MICROSOFT -->
<script type="text/javascript">
window.jQuery || document.write('<script src="https://ajax.aspnetcdn.com/ajax/jQuery/jquery-3.6.0.min.js"><\/script>');
</script>
<!-- IF THAT FAILS ************* WOW!!! *********** EMBED JQUERY FROM JQUERY.COM -->
<script type="text/javascript">
window.jQuery || document.write('<script src="https://code.jquery.com/jquery-3.6.0.min.js"><\/script>');
</script>
<!-- IF THAT FAILS ************* LET'S STOP!!! *********** EMBED JQUERY FROM PERSONAL COPY -->
<script type="text/javascript">
window.jQuery || document.write('<script src="jquery.min.js"><\/script>');
</script>
</head>
<body>
</body>
</html>
I have an HTML page where several JavaScript, CSS and images files are referenced. These references are dynamically injected and user can manually copy the HTML page and the support files to another machine.
If some JS or CSS are missing, the browser complains in the console. For example:
Error GET file:///E:/SSC_Temp/html_005/temp/Support/jquery.js
I need somehow these errors reported back to me on the inline JavaScript of the HTML page so I can ask user to first verify that support files are copied correctly.
There's the window.onerror event which just inform me that there's a JS error on the page such as an Unexpected Syntax error, but this doesn't fire in the event of a 404 Not Found error. I want to check for this condition in case of any resource type, including CSS, JS, and images.
I do not like to use jQuery AJAX to verify that file physically exists - the I/O overhead is expensive for every page load.
The error report has to contain the name of the file missing so I can check if the file is core or optional.
Any Ideas?
To capture all error events on the page, you can use addEventListener with the useCapture argument set to true. The reason window.onerror will not do this is because it uses the bubble event phase, and the error events you want to capture do not bubble.
If you add the following script to your HTML before you load any external content, you should be able to capture all the error events, even when loading offline.
<script type="text/javascript">
window.addEventListener('error', function(e) {
console.log(e);
}, true);
</script>
You can access the element that caused the error through e.target. For example, if you want to know what file did not load on an img tag, you can use e.target.src to get the URL that failed to load.
NOTE: This technically will not detect the error code, it detects if the image failed to load, as it technically behaves the same regardless of the status code. Depending on your setup this would probably be enough, but for example if a 404 is returned with a valid image it will not trigger an error event.
you can use the onload and onerror attributes to detect the error
for example upon loading the following html it gives alert error1 and error2 you can call your own function e.g onerror(logError(this);) and record them in an Array and once the page is fully loaded post is with single Ajax call.
<html>
<head>
<script src="file:///SSC_Temp/html_005/temp/Support/jquery.js" onerror="alert('error1');" onload="alert('load');" type="text/javascript" ></script>
</head>
<body>
<script src="file:///SSC_Temp/html_005/temp/Support/jquery.js" onerror="alert('error2');" onload="alert('load');" type="text/javascript" ></script>
</body>
</html>
I've put together the code below in pure JavaScript, tested, and it works.
All the source code (html, css, and Javascript) + images and example font is here: on github.
The first code block is an object with methods for specific file extensions: html and css.
The second is explained below, but here is a short description.
It does the following:
the function check_file takes 2 arguments: a string path and a callback function.
gets the contents of given path
gets the file extension (ext) of the given path
calls the srcFrom [ext] object method that returns an array of relative paths that was referenced in the string context by src, href, etc.
makes a synchronous call to each of these paths in the paths array
halts on error, and returns the HTTP error message and the path that had a problem, so you can use it for other issues as well, like 403 (forbidden), etc.
For convenience, it resolves to relative path names and does not care about which protocol is used (http or https, either is fine).
It also cleans up the DOM after parsing the CSS.
var srcFrom = // object
{
html:function(str)
{
var prs = new DOMParser();
var obj = prs.parseFromString(str, 'text/html');
var rsl = [], nds;
['data', 'href', 'src'].forEach(function(atr)
{
nds = [].slice.call(obj.querySelectorAll('['+atr+']'));
nds.forEach(function(nde)
{ rsl[rsl.length] = nde.getAttribute(atr); });
});
return rsl;
},
css:function(str)
{
var css = document.createElement('style');
var rsl = [], nds, tmp;
css.id = 'cssTest';
css.innerHTML = str;
document.head.appendChild(css);
css = [].slice.call(document.styleSheets);
for (var idx in css)
{
if (css[idx].ownerNode.id == 'cssTest')
{
[].slice.call(css[idx].cssRules).forEach(function(ssn)
{
['src', 'backgroundImage'].forEach(function(pty)
{
if (ssn.style[pty].length > 0)
{
tmp = ssn.style[pty].slice(4, -1);
tmp = tmp.split(window.location.pathname).join('');
tmp = tmp.split(window.location.origin).join('');
tmp = ((tmp[0] == '/') ? tmp.substr(1) : tmp);
rsl[rsl.length] = tmp;
}
});
});
break;
}
}
css = document.getElementById('cssTest');
css.parentNode.removeChild(css);
return rsl;
}
};
And here is the function that gets the file contents and calls the above object method according to the file extension:
function check_file(url, cbf)
{
var xhr = new XMLHttpRequest();
var uri = new XMLHttpRequest();
xhr.open('GET', url, true);
xhr.onload = function()
{
var ext = url.split('.').pop();
var lst = srcFrom[ext](this.response);
var rsl = [null, null], nds;
var Break = {};
try
{
lst.forEach(function(tgt)
{
uri.open('GET', tgt, false);
uri.send(null);
if (uri.statusText != 'OK')
{
rsl = [uri.statusText, tgt];
throw Break;
}
});
}
catch(e){}
cbf(rsl[0], rsl[1]);
};
xhr.send(null);
}
To use it, simply call it like this:
var uri = 'htm/stuff.html'; // html example
check_file(uri, function(err, pth)
{
if (err)
{ document.write('Aw Snap! "'+pth+'" is missing !'); }
});
Please feel free to comment and edit as you wish, i did this is a hurry, so it may not be so pretty :)
#alexander-omara gave the solution.
You can even add it in many files but the window handler can/should be added once.
I use the singleton pattern to achieve this:
some_global_object = {
error: (function(){
var activate = false;
return function(enable){
if(!activate){
activate = true;
window.addEventListener('error', function(e){
// maybe extra code here...
// if(e.target.custom_property)
// ...
}, true);
}
return activate;
};
}());
Now, from any context call it as many times you want as the handler is attached only once:
some_global_object.error();