Related
I'm dynamically adding <script> tags to a page's <head>, and I'd like to be able to tell whether the loading failed in some way -- a 404, a script error in the loaded script, whatever.
In Firefox, this works:
var script_tag = document.createElement('script');
script_tag.setAttribute('type', 'text/javascript');
script_tag.setAttribute('src', 'http://fail.org/nonexistant.js');
script_tag.onerror = function() { alert("Loading failed!"); }
document.getElementsByTagName('head')[0].appendChild(script_tag);
However, this doesn't work in IE or Safari.
Does anyone know of a way to make this work in browsers other than Firefox?
(I don't think a solution that requires placing special code within the .js files is a good one. It's inelegant and inflexible.)
UPDATE 2021:
All browsers today support onerror="" on script tags, examples:
Building script tag in js on MDN
Html example by #Rudey in comments: <script src="nonexistent.js" onerror="alert('error!')"></script>
Original comment from 2010:
If you only care about html5 browsers you can use error event.
From the spec:
If the src attribute's value is the
empty string or if it could not be
resolved, then the user agent must
queue a task to fire a simple event
named error at the element, and
abort these steps.
(...)
If the load resulted in an error (for
example a DNS error, or an HTTP 404
error) Executing the script block must
just consist of firing a simple event
named error at the element.
This means you don't have to do any error prone polling and can combine it with async and defer attribute to make sure the script is not blocking page rendering:
The defer attribute may be specified
even if the async attribute is
specified, to cause legacy Web
browsers that only support defer (and
not async) to fall back to the defer
behavior instead of the synchronous
blocking behavior that is the default.
More on http://www.w3.org/TR/html5/scripting-1.html#script
There is no error event for the script tag. You can tell when it is successful, and assume that it has not loaded after a timeout:
<script type="text/javascript" onload="loaded=1" src="....js"></script>
my working clean solution (2017)
function loaderScript(scriptUrl){
return new Promise(function (res, rej) {
let script = document.createElement('script');
script.src = scriptUrl;
script.type = 'text/javascript';
script.onerror = rej;
script.async = true;
script.onload = res;
script.addEventListener('error',rej);
script.addEventListener('load',res);
document.head.appendChild(script);
})
}
As Martin pointed, used like that:
const event = loaderScript("myscript.js")
.then(() => { console.log("loaded"); })
.catch(() => { console.log("error"); });
OR
try{
await loaderScript("myscript.js")
console.log("loaded");
}catch{
console.log("error");
}
The script from Erwinus works great, but isn't very clearly coded. I took the liberty to clean it up and decipher what it was doing. I've made these changes:
Meaningful variable names
Use of prototype.
require() uses an argument variable
No alert() messages are returned by default
Fixed some syntax errors and scope issues I was getting
Thanks again to Erwinus, the functionality itself is spot on.
function ScriptLoader() {
}
ScriptLoader.prototype = {
timer: function (times, // number of times to try
delay, // delay per try
delayMore, // extra delay per try (additional to delay)
test, // called each try, timer stops if this returns true
failure, // called on failure
result // used internally, shouldn't be passed
) {
var me = this;
if (times == -1 || times > 0) {
setTimeout(function () {
result = (test()) ? 1 : 0;
me.timer((result) ? 0 : (times > 0) ? --times : times, delay + ((delayMore) ? delayMore : 0), delayMore, test, failure, result);
}, (result || delay < 0) ? 0.1 : delay);
} else if (typeof failure == 'function') {
setTimeout(failure, 1);
}
},
addEvent: function (el, eventName, eventFunc) {
if (typeof el != 'object') {
return false;
}
if (el.addEventListener) {
el.addEventListener(eventName, eventFunc, false);
return true;
}
if (el.attachEvent) {
el.attachEvent("on" + eventName, eventFunc);
return true;
}
return false;
},
// add script to dom
require: function (url, args) {
var me = this;
args = args || {};
var scriptTag = document.createElement('script');
var headTag = document.getElementsByTagName('head')[0];
if (!headTag) {
return false;
}
setTimeout(function () {
var f = (typeof args.success == 'function') ? args.success : function () {
};
args.failure = (typeof args.failure == 'function') ? args.failure : function () {
};
var fail = function () {
if (!scriptTag.__es) {
scriptTag.__es = true;
scriptTag.id = 'failed';
args.failure(scriptTag);
}
};
scriptTag.onload = function () {
scriptTag.id = 'loaded';
f(scriptTag);
};
scriptTag.type = 'text/javascript';
scriptTag.async = (typeof args.async == 'boolean') ? args.async : false;
scriptTag.charset = 'utf-8';
me.__es = false;
me.addEvent(scriptTag, 'error', fail); // when supported
// when error event is not supported fall back to timer
me.timer(15, 1000, 0, function () {
return (scriptTag.id == 'loaded');
}, function () {
if (scriptTag.id != 'loaded') {
fail();
}
});
scriptTag.src = url;
setTimeout(function () {
try {
headTag.appendChild(scriptTag);
} catch (e) {
fail();
}
}, 1);
}, (typeof args.delay == 'number') ? args.delay : 1);
return true;
}
};
$(document).ready(function () {
var loader = new ScriptLoader();
loader.require('resources/templates.js', {
async: true, success: function () {
alert('loaded');
}, failure: function () {
alert('NOT loaded');
}
});
});
I know this is an old thread but I got a nice solution to you (I think). It's copied from an class of mine, that handles all AJAX stuff.
When the script cannot be loaded, it set an error handler but when the error handler is not supported, it falls back to a timer that checks for errors for 15 seconds.
function jsLoader()
{
var o = this;
// simple unstopable repeat timer, when t=-1 means endless, when function f() returns true it can be stopped
o.timer = function(t, i, d, f, fend, b)
{
if( t == -1 || t > 0 )
{
setTimeout(function() {
b=(f()) ? 1 : 0;
o.timer((b) ? 0 : (t>0) ? --t : t, i+((d) ? d : 0), d, f, fend,b );
}, (b || i < 0) ? 0.1 : i);
}
else if(typeof fend == 'function')
{
setTimeout(fend, 1);
}
};
o.addEvent = function(el, eventName, eventFunc)
{
if(typeof el != 'object')
{
return false;
}
if(el.addEventListener)
{
el.addEventListener (eventName, eventFunc, false);
return true;
}
if(el.attachEvent)
{
el.attachEvent("on" + eventName, eventFunc);
return true;
}
return false;
};
// add script to dom
o.require = function(s, delay, baSync, fCallback, fErr)
{
var oo = document.createElement('script'),
oHead = document.getElementsByTagName('head')[0];
if(!oHead)
{
return false;
}
setTimeout( function() {
var f = (typeof fCallback == 'function') ? fCallback : function(){};
fErr = (typeof fErr == 'function') ? fErr : function(){
alert('require: Cannot load resource -'+s);
},
fe = function(){
if(!oo.__es)
{
oo.__es = true;
oo.id = 'failed';
fErr(oo);
}
};
oo.onload = function() {
oo.id = 'loaded';
f(oo);
};
oo.type = 'text/javascript';
oo.async = (typeof baSync == 'boolean') ? baSync : false;
oo.charset = 'utf-8';
o.__es = false;
o.addEvent( oo, 'error', fe ); // when supported
// when error event is not supported fall back to timer
o.timer(15, 1000, 0, function() {
return (oo.id == 'loaded');
}, function(){
if(oo.id != 'loaded'){
fe();
}
});
oo.src = s;
setTimeout(function() {
try{
oHead.appendChild(oo);
}catch(e){
fe();
}
},1);
}, (typeof delay == 'number') ? delay : 1);
return true;
};
}
$(document).ready( function()
{
var ol = new jsLoader();
ol.require('myscript.js', 800, true, function(){
alert('loaded');
}, function() {
alert('NOT loaded');
});
});
To check if the javascript in nonexistant.js returned no error you have to add a variable inside http://fail.org/nonexistant.js like var isExecuted = true; and then check if it exists when the script tag is loaded.
However if you only want to check that the nonexistant.js returned without a 404 (meaning it exists), you can try with a isLoaded variable ...
var isExecuted = false;
var isLoaded = false;
script_tag.onload = script_tag.onreadystatechange = function() {
if(!this.readyState ||
this.readyState == "loaded" || this.readyState == "complete") {
// script successfully loaded
isLoaded = true;
if(isExecuted) // no error
}
}
This will cover both cases.
I hope this doesn't get downvoted, because in special circumstances it is the most reliable way to solve the problem. Any time the server allows you to get a Javascript resource using CORS (http://en.wikipedia.org/wiki/Cross-origin_resource_sharing), you have a rich array of options to do so.
Using XMLHttpRequest to fetch resources will work across all modern browsers, including IE. Since you are looking to load Javascript, you have Javascript available to you in the first place. You can track the progress using the readyState (http://en.wikipedia.org/wiki/XMLHttpRequest#The_onreadystatechange_event_listener). Finally, once you receive the content of the file, you can execute it with eval ( ). Yes, I said eval -- because security-wise it is no different from loading the script normally. In fact, a similar technique is suggested by John Resig to have nicer tags (http://ejohn.org/blog/degrading-script-tags/).
This method also lets you separate the loading from the eval, and execute functions before and after the eval happens. It becomes very useful when loading scripts in parallel but evaluating them one after the other -- something browsers can do easily when you place the tags in HTML, but don't let you by adding scripts at run-time with Javascript.
CORS is also preferable to JSONP for loading scripts (http://en.wikipedia.org/wiki/XMLHttpRequest#Cross-domain_requests). However, if you are developing your own third-party widgets to be embedded in other sites, you should actually load the Javascript files from your own domain in your own iframe (again, using AJAX)
In short:
Try to see if you can load the resource using AJAX GET
Use eval after it has successfully loaded
To improve it:
Check out the cache-control headers being sent
Look into otherwise caching the content in localStorage, if you need to
Check out Resig's "degrading javascript" for cleaner code
Check out require.js
This trick worked for me, although I admit that this is probably not the best way to solve this problem. Instead of trying this, you should see why the javascripts aren't loading. Try keeping a local copy of the script in your server, etc. or check with the third party vendor from where you are trying to download the script.
Anyways, so here's the workaround:
1) Initialize a variable to false
2) Set it to true when the javascript loads (using the onload attribute)
3) check if the variable is true or false once the HTML body has loaded
<html>
<head>
<script>
var scriptLoaded = false;
function checkScriptLoaded() {
if (scriptLoaded) {
// do something here
} else {
// do something else here!
}
}
</script>
<script src="http://some-external-script.js" onload="scriptLoaded=true;" />
</head>
<body onload="checkScriptLoaded()">
<p>My Test Page!</p>
</body>
</html>
Here is another JQuery-based solution without any timers:
<script type="text/javascript">
function loadScript(url, onsuccess, onerror) {
$.get(url)
.done(function() {
// File/url exists
console.log("JS Loader: file exists, executing $.getScript "+url)
$.getScript(url, function() {
if (onsuccess) {
console.log("JS Loader: Ok, loaded. Calling onsuccess() for " + url);
onsuccess();
console.log("JS Loader: done with onsuccess() for " + url);
} else {
console.log("JS Loader: Ok, loaded, no onsuccess() callback " + url)
}
});
}).fail(function() {
// File/url does not exist
if (onerror) {
console.error("JS Loader: probably 404 not found. Not calling $.getScript. Calling onerror() for " + url);
onerror();
console.error("JS Loader: done with onerror() for " + url);
} else {
console.error("JS Loader: probably 404 not found. Not calling $.getScript. No onerror() callback " + url);
}
});
}
</script>
Thanks to:
https://stackoverflow.com/a/14691735/1243926
Sample usage (original sample from JQuery getScript documentation):
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>jQuery.getScript demo</title>
<style>
.block {
background-color: blue;
width: 150px;
height: 70px;
margin: 10px;
}
</style>
<script src="http://code.jquery.com/jquery-1.9.1.js"></script>
</head>
<body>
<button id="go">» Run</button>
<div class="block"></div>
<script>
function loadScript(url, onsuccess, onerror) {
$.get(url)
.done(function() {
// File/url exists
console.log("JS Loader: file exists, executing $.getScript "+url)
$.getScript(url, function() {
if (onsuccess) {
console.log("JS Loader: Ok, loaded. Calling onsuccess() for " + url);
onsuccess();
console.log("JS Loader: done with onsuccess() for " + url);
} else {
console.log("JS Loader: Ok, loaded, no onsuccess() callback " + url)
}
});
}).fail(function() {
// File/url does not exist
if (onerror) {
console.error("JS Loader: probably 404 not found. Not calling $.getScript. Calling onerror() for " + url);
onerror();
console.error("JS Loader: done with onerror() for " + url);
} else {
console.error("JS Loader: probably 404 not found. Not calling $.getScript. No onerror() callback " + url);
}
});
}
loadScript("https://raw.github.com/jquery/jquery-color/master/jquery.color.js", function() {
console.log("loaded jquery-color");
$( "#go" ).click(function() {
$( ".block" )
.animate({
backgroundColor: "rgb(255, 180, 180)"
}, 1000 )
.delay( 500 )
.animate({
backgroundColor: "olive"
}, 1000 )
.delay( 500 )
.animate({
backgroundColor: "#00f"
}, 1000 );
});
}, function() { console.error("Cannot load jquery-color"); });
</script>
</body>
</html>
This can be done safely using promises
function loadScript(src) {
return new Promise(function(resolve, reject) {
let script = document.createElement('script');
script.src = src;
script.onload = () => resolve(script);
script.onerror = () => reject(new Error("Script load error: " + src));
document.head.append(script);
});
}
and use like this
let promise = loadScript("https://cdnjs.cloudflare.com/ajax/libs/lodash.js/3.2.0/lodash.js");
promise.then(
script => alert(`${script.src} is loaded!`),
error => alert(`Error: ${error.message}`)
);
onerror Event
*Update August 2017: onerror is fired by Chrome and Firefox. onload is fired by Internet Explorer. Edge fires neither onerror nor onload. I wouldnt use this method but it could work in some cases. See also
<link> onerror do not work in IE
*
Definition and Usage
The onerror event is triggered if an error occurs while loading an external file (e.g. a document or an image).
Tip: When used on audio/video media, related events that occurs when there is some kind of disturbance to the media loading process, are:
onabort
onemptied
onstalled
onsuspend
In HTML:
element onerror="myScript">
In JavaScript, using the addEventListener() method:
object.addEventListener("error", myScript);
Note: The addEventListener() method is not supported in Internet Explorer 8 and earlier versions.
Example
Execute a JavaScript if an error occurs when loading an image:
img src="image.gif" onerror="myFunction()">
The reason it doesn't work in Safari is because you're using attribute syntax. This will work fine though:
script_tag.addEventListener('error', function(){/*...*/}, true);
...except in IE.
If you want to check the script executed successfully, just set a variable using that script and check for it being set in the outer code.
This doesn't need jquery, doesn't need to load the script async, needs no timer nor to have the loaded script set a value. I've tested it in FF, Chrome, and Safari.
<script>
function loadScript(src) {
return new Promise(function(resolve, reject) {
let s = window.document.createElement("SCRIPT");
s.onload = () => resolve(s);
s.onerror = () => reject(new Error(src));
s.src = src;
// don't bounce to global handler on 404.
s.addEventListener('error', function() {});
window.document.head.append(s);
});
}
let successCallback = (result) => {
console.log(scriptUrl + " loaded.");
}
let failureCallback = (error) => {
console.log("load failed: " + error.message);
}
loadScript(scriptUrl).then(successCallback, failureCallback);
</script>
It was proposed to set a timeout and then assume load failure after a timeout.
setTimeout(fireCustomOnerror, 4000);
The problem with that approach is that the assumption is based on chance. After your timeout expires, the request is still pending. The request for the pending script may load, even after the programmer assumed that load won't happen.
If the request could be canceled, then the program could wait for a period, then cancel the request.
This is how I used a promise to detect loading errors that are emited on the window object:
<script type='module'>
window.addEventListener('error', function(error) {
let url = error.filename
url = url.substring(0, (url.indexOf("#") == -1) ? url.length : url.indexOf("#"));
url = url.substring(0, (url.indexOf("?") == -1) ? url.length : url.indexOf("?"));
url = url.substring(url.lastIndexOf("/") + 1, url.length);
window.scriptLoadReject && window.scriptLoadReject[url] && window.scriptLoadReject[url](error);
}, true);
window.boot=function boot() {
const t=document.createElement('script');
t.id='index.mjs';
t.type='module';
new Promise((resolve, reject) => {
window.scriptLoadReject = window.scriptLoadReject || {};
window.scriptLoadReject[t.id] = reject;
t.addEventListener('error', reject);
t.addEventListener('load', resolve); // Careful load is sometimes called even if errors prevent your script from running! This promise is only meant to catch errors while loading the file.
}).catch((value) => {
document.body.innerHTML='Error loading ' + t.id + '! Please reload this webpage.<br/>If this error persists, please try again later.<div><br/>' + t.id + ':' + value.lineno + ':' + value.colno + '<br/>' + (value && value.message);
});
t.src='./index.mjs'+'?'+new Date().getTime();
document.head.appendChild(t);
};
</script>
<script nomodule>document.body.innerHTML='This website needs ES6 Modules!<br/>Please enable ES6 Modules and then reload this webpage.';</script>
</head>
<body onload="boot()" style="margin: 0;border: 0;padding: 0;text-align: center;">
<noscript>This website needs JavaScript!<br/>Please enable JavaScript and then reload this webpage.</noscript>
Well, the only way I can think of doing everything you want is pretty ugly. First perform an AJAX call to retrieve the Javascript file contents. When this completes you can check the status code to decide if this was successful or not. Then take the responseText from the xhr object and wrap it in a try/catch, dynamically create a script tag, and for IE you can set the text property of the script tag to the JS text, in all other browsers you should be able to append a text node with the contents to script tag. If there's any code that expects a script tag to actually contain the src location of the file, this won't work, but it should be fine for most situations.
I'm loading data.js into my a.html page.
In my data.js, i am checking if a.html has jquery and loading it if not. Right after loading jquery i am making an ajax call but i am getting
$ is not defined
exception.
Here is my data.js
if(typeof jQuery=='undefined') {
var headTag = document.getElementsByTagName("head")[0];
var jqTag = document.createElement('script');
jqTag.type = 'text/javascript';
jqTag.src = 'http://localhost:8001/jquery-min.js';
headTag.appendChild(jqTag);
}
var url = 'http://127.0.0.1:5000';
$.ajax({
url: url,
success: function(data) {
$("#" + containerId).html(data);
},
error: function(e) {
console.log(e.message);
}
});
From developer console, i can see jquery is loaded. I can see it in both Resources and head tag.
The jQuery (and $ thus) isn't loaded yet when you make the AJAX call since you only just added the script tag to your DOM. After that it starts the downloading. Instead you should bind the onload event of script tag and perform the actions after it has been loaded.
Example
jqTag.onload = function() {
var url = 'http://127.0.0.1:5000';
$.ajax({
url: url,
success: function(data) {
$("#" + containerId).html(data);
},
error: function(e) {
console.log(e.message);
}
});
}
jqTag.src = 'http://localhost:8001/jquery-min.js';
change this Line :
if(typeof jQuery=='undefined')
to
if(typeof jQuery== undefined ) {
I have a script that I have no control over and is on another domain. The default procedure is to just include it in a script tag and it runs fine.
I don't want to run it by default so I have an if statement and if true I want to run the script.
So default option is:
<script src="http://domain/site/script?Id=12345&delayMs=2000&stayMs=10000&chance=0.1" type="text/javascript" ></script>
I taught I could just use jQuery.getScript() to get it to run the above url but this does not work. I do not know the correct link to the actual script and functions contained so I cannot getScript and call functions.
Any ideas would help.
Regards
Brian
Since you're having cross domain issues, try this ($.getScript() is just a shorthand for this anyway, with the exception of crossDomain: true).
$.ajax({
url: 'http://domain/site/script?Id=12345&delayMs=2000&
stayMs=10000&chance=0.1',
crossDomain: true,
dataType: 'script',
success: function () {
// script is loaded
},
error: function () {
// handle errors
}
});
Another solution you can try using pure JS:
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.parent.insertBefore(s, t);
}
Usage:
var url = 'http://domain/site/script?Id=12345&delayMs=2000&
stayMs=10000&chance=0.1';
loadScript(url, function(){
console.log('script loaded');
});
today I've been working on loading dynamic javascript code (files). The solution I use is :
function loadScript(scriptUrl) {
var head = document.getElementsByTagName("head")[0];
var script = document.createElement('script');
script.id = 'uploadScript';
script.type = 'text/javascript';
script.src = scriptUrl;
head.appendChild(script);
}
the problem with this is that I don't know how to make sure WHEN the script contents are executed. Since the script contains classes (well JS classes), I wrote down a function that is called through setTimeout and checks if those objects are defined. This is not flexible as it is not automatical. So? Are there ways to load those scripts and have a reliable notification on when they have been executed?
You can use jquery's getScript and pass a callback function.
$.getScript("test.js", function(){
alert("Script loaded and executed.");
});
See: jquery.
The easiest way short of a JS library is to make an XMLHttpRequest and eval() the return. Your "onload" would be when the data is returned, and "oninit" would be right after you've eval'd.
EDIT: If you want to sequence this, you can create an AssetLoader that takes an array of scripts and won't eval() a script until the one preceding it has been fetched and initialized.
EDIT 2: You can also use the script.onload stuff in the post referenced in the comments. The eval method has a slight advantage in that you can separate and control the load and execution portions of the script import.
EDIT 3: Here's an example. Consider a file called foo.js that contains the following:
function foo () {
alert('bar');
}
Then execute the following from another page in your browser:
function initScript (scriptString) {
window.eval(scriptString);
}
function getScript (url, loadCallback, initCallback, callbackScope) {
var req = new XMLHttpRequest();
req.open('GET', url);
req.onreadystatechange = function (e) {
if (req.readyState == 4) {
if (loadCallback) loadCallback.apply(callbackScope);
initScript.call(null, req.responseText);
if (initCallback) initCallback.apply(callbackScope);
}
}
req.send();
}
function fooScriptLoaded () {
alert('script loaded');
}
function fooScriptInitialized () {
alert('script initialized');
foo();
}
window.onload = function () {
getScript('foo.js', fooScriptLoaded, fooScriptInitialized, null);
}
You will see the alerts "script loaded", "script initialized", and "bar". Obviously the implementation of XMLHttpRequest here isn't complete and there are all sorts of things you can do for whatever scope you want to execute the script in, but this is the core of it.
You could use a counter variable, and a kind of callback:
var scriptsToLoad = 10;
var loadedScripts = 0;
//...
function increaseLoadCount() {
loadedScripts++;
if(loadedScripts == scriptsToLoad) {
alert("start here");
}
}
//script1-10.js
increaseLoadCount();
Maybe a bit nicer than with a timeout..
I'm dynamically adding <script> tags to a page's <head>, and I'd like to be able to tell whether the loading failed in some way -- a 404, a script error in the loaded script, whatever.
In Firefox, this works:
var script_tag = document.createElement('script');
script_tag.setAttribute('type', 'text/javascript');
script_tag.setAttribute('src', 'http://fail.org/nonexistant.js');
script_tag.onerror = function() { alert("Loading failed!"); }
document.getElementsByTagName('head')[0].appendChild(script_tag);
However, this doesn't work in IE or Safari.
Does anyone know of a way to make this work in browsers other than Firefox?
(I don't think a solution that requires placing special code within the .js files is a good one. It's inelegant and inflexible.)
UPDATE 2021:
All browsers today support onerror="" on script tags, examples:
Building script tag in js on MDN
Html example by #Rudey in comments: <script src="nonexistent.js" onerror="alert('error!')"></script>
Original comment from 2010:
If you only care about html5 browsers you can use error event.
From the spec:
If the src attribute's value is the
empty string or if it could not be
resolved, then the user agent must
queue a task to fire a simple event
named error at the element, and
abort these steps.
(...)
If the load resulted in an error (for
example a DNS error, or an HTTP 404
error) Executing the script block must
just consist of firing a simple event
named error at the element.
This means you don't have to do any error prone polling and can combine it with async and defer attribute to make sure the script is not blocking page rendering:
The defer attribute may be specified
even if the async attribute is
specified, to cause legacy Web
browsers that only support defer (and
not async) to fall back to the defer
behavior instead of the synchronous
blocking behavior that is the default.
More on http://www.w3.org/TR/html5/scripting-1.html#script
There is no error event for the script tag. You can tell when it is successful, and assume that it has not loaded after a timeout:
<script type="text/javascript" onload="loaded=1" src="....js"></script>
my working clean solution (2017)
function loaderScript(scriptUrl){
return new Promise(function (res, rej) {
let script = document.createElement('script');
script.src = scriptUrl;
script.type = 'text/javascript';
script.onerror = rej;
script.async = true;
script.onload = res;
script.addEventListener('error',rej);
script.addEventListener('load',res);
document.head.appendChild(script);
})
}
As Martin pointed, used like that:
const event = loaderScript("myscript.js")
.then(() => { console.log("loaded"); })
.catch(() => { console.log("error"); });
OR
try{
await loaderScript("myscript.js")
console.log("loaded");
}catch{
console.log("error");
}
The script from Erwinus works great, but isn't very clearly coded. I took the liberty to clean it up and decipher what it was doing. I've made these changes:
Meaningful variable names
Use of prototype.
require() uses an argument variable
No alert() messages are returned by default
Fixed some syntax errors and scope issues I was getting
Thanks again to Erwinus, the functionality itself is spot on.
function ScriptLoader() {
}
ScriptLoader.prototype = {
timer: function (times, // number of times to try
delay, // delay per try
delayMore, // extra delay per try (additional to delay)
test, // called each try, timer stops if this returns true
failure, // called on failure
result // used internally, shouldn't be passed
) {
var me = this;
if (times == -1 || times > 0) {
setTimeout(function () {
result = (test()) ? 1 : 0;
me.timer((result) ? 0 : (times > 0) ? --times : times, delay + ((delayMore) ? delayMore : 0), delayMore, test, failure, result);
}, (result || delay < 0) ? 0.1 : delay);
} else if (typeof failure == 'function') {
setTimeout(failure, 1);
}
},
addEvent: function (el, eventName, eventFunc) {
if (typeof el != 'object') {
return false;
}
if (el.addEventListener) {
el.addEventListener(eventName, eventFunc, false);
return true;
}
if (el.attachEvent) {
el.attachEvent("on" + eventName, eventFunc);
return true;
}
return false;
},
// add script to dom
require: function (url, args) {
var me = this;
args = args || {};
var scriptTag = document.createElement('script');
var headTag = document.getElementsByTagName('head')[0];
if (!headTag) {
return false;
}
setTimeout(function () {
var f = (typeof args.success == 'function') ? args.success : function () {
};
args.failure = (typeof args.failure == 'function') ? args.failure : function () {
};
var fail = function () {
if (!scriptTag.__es) {
scriptTag.__es = true;
scriptTag.id = 'failed';
args.failure(scriptTag);
}
};
scriptTag.onload = function () {
scriptTag.id = 'loaded';
f(scriptTag);
};
scriptTag.type = 'text/javascript';
scriptTag.async = (typeof args.async == 'boolean') ? args.async : false;
scriptTag.charset = 'utf-8';
me.__es = false;
me.addEvent(scriptTag, 'error', fail); // when supported
// when error event is not supported fall back to timer
me.timer(15, 1000, 0, function () {
return (scriptTag.id == 'loaded');
}, function () {
if (scriptTag.id != 'loaded') {
fail();
}
});
scriptTag.src = url;
setTimeout(function () {
try {
headTag.appendChild(scriptTag);
} catch (e) {
fail();
}
}, 1);
}, (typeof args.delay == 'number') ? args.delay : 1);
return true;
}
};
$(document).ready(function () {
var loader = new ScriptLoader();
loader.require('resources/templates.js', {
async: true, success: function () {
alert('loaded');
}, failure: function () {
alert('NOT loaded');
}
});
});
I know this is an old thread but I got a nice solution to you (I think). It's copied from an class of mine, that handles all AJAX stuff.
When the script cannot be loaded, it set an error handler but when the error handler is not supported, it falls back to a timer that checks for errors for 15 seconds.
function jsLoader()
{
var o = this;
// simple unstopable repeat timer, when t=-1 means endless, when function f() returns true it can be stopped
o.timer = function(t, i, d, f, fend, b)
{
if( t == -1 || t > 0 )
{
setTimeout(function() {
b=(f()) ? 1 : 0;
o.timer((b) ? 0 : (t>0) ? --t : t, i+((d) ? d : 0), d, f, fend,b );
}, (b || i < 0) ? 0.1 : i);
}
else if(typeof fend == 'function')
{
setTimeout(fend, 1);
}
};
o.addEvent = function(el, eventName, eventFunc)
{
if(typeof el != 'object')
{
return false;
}
if(el.addEventListener)
{
el.addEventListener (eventName, eventFunc, false);
return true;
}
if(el.attachEvent)
{
el.attachEvent("on" + eventName, eventFunc);
return true;
}
return false;
};
// add script to dom
o.require = function(s, delay, baSync, fCallback, fErr)
{
var oo = document.createElement('script'),
oHead = document.getElementsByTagName('head')[0];
if(!oHead)
{
return false;
}
setTimeout( function() {
var f = (typeof fCallback == 'function') ? fCallback : function(){};
fErr = (typeof fErr == 'function') ? fErr : function(){
alert('require: Cannot load resource -'+s);
},
fe = function(){
if(!oo.__es)
{
oo.__es = true;
oo.id = 'failed';
fErr(oo);
}
};
oo.onload = function() {
oo.id = 'loaded';
f(oo);
};
oo.type = 'text/javascript';
oo.async = (typeof baSync == 'boolean') ? baSync : false;
oo.charset = 'utf-8';
o.__es = false;
o.addEvent( oo, 'error', fe ); // when supported
// when error event is not supported fall back to timer
o.timer(15, 1000, 0, function() {
return (oo.id == 'loaded');
}, function(){
if(oo.id != 'loaded'){
fe();
}
});
oo.src = s;
setTimeout(function() {
try{
oHead.appendChild(oo);
}catch(e){
fe();
}
},1);
}, (typeof delay == 'number') ? delay : 1);
return true;
};
}
$(document).ready( function()
{
var ol = new jsLoader();
ol.require('myscript.js', 800, true, function(){
alert('loaded');
}, function() {
alert('NOT loaded');
});
});
To check if the javascript in nonexistant.js returned no error you have to add a variable inside http://fail.org/nonexistant.js like var isExecuted = true; and then check if it exists when the script tag is loaded.
However if you only want to check that the nonexistant.js returned without a 404 (meaning it exists), you can try with a isLoaded variable ...
var isExecuted = false;
var isLoaded = false;
script_tag.onload = script_tag.onreadystatechange = function() {
if(!this.readyState ||
this.readyState == "loaded" || this.readyState == "complete") {
// script successfully loaded
isLoaded = true;
if(isExecuted) // no error
}
}
This will cover both cases.
I hope this doesn't get downvoted, because in special circumstances it is the most reliable way to solve the problem. Any time the server allows you to get a Javascript resource using CORS (http://en.wikipedia.org/wiki/Cross-origin_resource_sharing), you have a rich array of options to do so.
Using XMLHttpRequest to fetch resources will work across all modern browsers, including IE. Since you are looking to load Javascript, you have Javascript available to you in the first place. You can track the progress using the readyState (http://en.wikipedia.org/wiki/XMLHttpRequest#The_onreadystatechange_event_listener). Finally, once you receive the content of the file, you can execute it with eval ( ). Yes, I said eval -- because security-wise it is no different from loading the script normally. In fact, a similar technique is suggested by John Resig to have nicer tags (http://ejohn.org/blog/degrading-script-tags/).
This method also lets you separate the loading from the eval, and execute functions before and after the eval happens. It becomes very useful when loading scripts in parallel but evaluating them one after the other -- something browsers can do easily when you place the tags in HTML, but don't let you by adding scripts at run-time with Javascript.
CORS is also preferable to JSONP for loading scripts (http://en.wikipedia.org/wiki/XMLHttpRequest#Cross-domain_requests). However, if you are developing your own third-party widgets to be embedded in other sites, you should actually load the Javascript files from your own domain in your own iframe (again, using AJAX)
In short:
Try to see if you can load the resource using AJAX GET
Use eval after it has successfully loaded
To improve it:
Check out the cache-control headers being sent
Look into otherwise caching the content in localStorage, if you need to
Check out Resig's "degrading javascript" for cleaner code
Check out require.js
This trick worked for me, although I admit that this is probably not the best way to solve this problem. Instead of trying this, you should see why the javascripts aren't loading. Try keeping a local copy of the script in your server, etc. or check with the third party vendor from where you are trying to download the script.
Anyways, so here's the workaround:
1) Initialize a variable to false
2) Set it to true when the javascript loads (using the onload attribute)
3) check if the variable is true or false once the HTML body has loaded
<html>
<head>
<script>
var scriptLoaded = false;
function checkScriptLoaded() {
if (scriptLoaded) {
// do something here
} else {
// do something else here!
}
}
</script>
<script src="http://some-external-script.js" onload="scriptLoaded=true;" />
</head>
<body onload="checkScriptLoaded()">
<p>My Test Page!</p>
</body>
</html>
Here is another JQuery-based solution without any timers:
<script type="text/javascript">
function loadScript(url, onsuccess, onerror) {
$.get(url)
.done(function() {
// File/url exists
console.log("JS Loader: file exists, executing $.getScript "+url)
$.getScript(url, function() {
if (onsuccess) {
console.log("JS Loader: Ok, loaded. Calling onsuccess() for " + url);
onsuccess();
console.log("JS Loader: done with onsuccess() for " + url);
} else {
console.log("JS Loader: Ok, loaded, no onsuccess() callback " + url)
}
});
}).fail(function() {
// File/url does not exist
if (onerror) {
console.error("JS Loader: probably 404 not found. Not calling $.getScript. Calling onerror() for " + url);
onerror();
console.error("JS Loader: done with onerror() for " + url);
} else {
console.error("JS Loader: probably 404 not found. Not calling $.getScript. No onerror() callback " + url);
}
});
}
</script>
Thanks to:
https://stackoverflow.com/a/14691735/1243926
Sample usage (original sample from JQuery getScript documentation):
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>jQuery.getScript demo</title>
<style>
.block {
background-color: blue;
width: 150px;
height: 70px;
margin: 10px;
}
</style>
<script src="http://code.jquery.com/jquery-1.9.1.js"></script>
</head>
<body>
<button id="go">» Run</button>
<div class="block"></div>
<script>
function loadScript(url, onsuccess, onerror) {
$.get(url)
.done(function() {
// File/url exists
console.log("JS Loader: file exists, executing $.getScript "+url)
$.getScript(url, function() {
if (onsuccess) {
console.log("JS Loader: Ok, loaded. Calling onsuccess() for " + url);
onsuccess();
console.log("JS Loader: done with onsuccess() for " + url);
} else {
console.log("JS Loader: Ok, loaded, no onsuccess() callback " + url)
}
});
}).fail(function() {
// File/url does not exist
if (onerror) {
console.error("JS Loader: probably 404 not found. Not calling $.getScript. Calling onerror() for " + url);
onerror();
console.error("JS Loader: done with onerror() for " + url);
} else {
console.error("JS Loader: probably 404 not found. Not calling $.getScript. No onerror() callback " + url);
}
});
}
loadScript("https://raw.github.com/jquery/jquery-color/master/jquery.color.js", function() {
console.log("loaded jquery-color");
$( "#go" ).click(function() {
$( ".block" )
.animate({
backgroundColor: "rgb(255, 180, 180)"
}, 1000 )
.delay( 500 )
.animate({
backgroundColor: "olive"
}, 1000 )
.delay( 500 )
.animate({
backgroundColor: "#00f"
}, 1000 );
});
}, function() { console.error("Cannot load jquery-color"); });
</script>
</body>
</html>
This can be done safely using promises
function loadScript(src) {
return new Promise(function(resolve, reject) {
let script = document.createElement('script');
script.src = src;
script.onload = () => resolve(script);
script.onerror = () => reject(new Error("Script load error: " + src));
document.head.append(script);
});
}
and use like this
let promise = loadScript("https://cdnjs.cloudflare.com/ajax/libs/lodash.js/3.2.0/lodash.js");
promise.then(
script => alert(`${script.src} is loaded!`),
error => alert(`Error: ${error.message}`)
);
onerror Event
*Update August 2017: onerror is fired by Chrome and Firefox. onload is fired by Internet Explorer. Edge fires neither onerror nor onload. I wouldnt use this method but it could work in some cases. See also
<link> onerror do not work in IE
*
Definition and Usage
The onerror event is triggered if an error occurs while loading an external file (e.g. a document or an image).
Tip: When used on audio/video media, related events that occurs when there is some kind of disturbance to the media loading process, are:
onabort
onemptied
onstalled
onsuspend
In HTML:
element onerror="myScript">
In JavaScript, using the addEventListener() method:
object.addEventListener("error", myScript);
Note: The addEventListener() method is not supported in Internet Explorer 8 and earlier versions.
Example
Execute a JavaScript if an error occurs when loading an image:
img src="image.gif" onerror="myFunction()">
The reason it doesn't work in Safari is because you're using attribute syntax. This will work fine though:
script_tag.addEventListener('error', function(){/*...*/}, true);
...except in IE.
If you want to check the script executed successfully, just set a variable using that script and check for it being set in the outer code.
This doesn't need jquery, doesn't need to load the script async, needs no timer nor to have the loaded script set a value. I've tested it in FF, Chrome, and Safari.
<script>
function loadScript(src) {
return new Promise(function(resolve, reject) {
let s = window.document.createElement("SCRIPT");
s.onload = () => resolve(s);
s.onerror = () => reject(new Error(src));
s.src = src;
// don't bounce to global handler on 404.
s.addEventListener('error', function() {});
window.document.head.append(s);
});
}
let successCallback = (result) => {
console.log(scriptUrl + " loaded.");
}
let failureCallback = (error) => {
console.log("load failed: " + error.message);
}
loadScript(scriptUrl).then(successCallback, failureCallback);
</script>
It was proposed to set a timeout and then assume load failure after a timeout.
setTimeout(fireCustomOnerror, 4000);
The problem with that approach is that the assumption is based on chance. After your timeout expires, the request is still pending. The request for the pending script may load, even after the programmer assumed that load won't happen.
If the request could be canceled, then the program could wait for a period, then cancel the request.
This is how I used a promise to detect loading errors that are emited on the window object:
<script type='module'>
window.addEventListener('error', function(error) {
let url = error.filename
url = url.substring(0, (url.indexOf("#") == -1) ? url.length : url.indexOf("#"));
url = url.substring(0, (url.indexOf("?") == -1) ? url.length : url.indexOf("?"));
url = url.substring(url.lastIndexOf("/") + 1, url.length);
window.scriptLoadReject && window.scriptLoadReject[url] && window.scriptLoadReject[url](error);
}, true);
window.boot=function boot() {
const t=document.createElement('script');
t.id='index.mjs';
t.type='module';
new Promise((resolve, reject) => {
window.scriptLoadReject = window.scriptLoadReject || {};
window.scriptLoadReject[t.id] = reject;
t.addEventListener('error', reject);
t.addEventListener('load', resolve); // Careful load is sometimes called even if errors prevent your script from running! This promise is only meant to catch errors while loading the file.
}).catch((value) => {
document.body.innerHTML='Error loading ' + t.id + '! Please reload this webpage.<br/>If this error persists, please try again later.<div><br/>' + t.id + ':' + value.lineno + ':' + value.colno + '<br/>' + (value && value.message);
});
t.src='./index.mjs'+'?'+new Date().getTime();
document.head.appendChild(t);
};
</script>
<script nomodule>document.body.innerHTML='This website needs ES6 Modules!<br/>Please enable ES6 Modules and then reload this webpage.';</script>
</head>
<body onload="boot()" style="margin: 0;border: 0;padding: 0;text-align: center;">
<noscript>This website needs JavaScript!<br/>Please enable JavaScript and then reload this webpage.</noscript>
Well, the only way I can think of doing everything you want is pretty ugly. First perform an AJAX call to retrieve the Javascript file contents. When this completes you can check the status code to decide if this was successful or not. Then take the responseText from the xhr object and wrap it in a try/catch, dynamically create a script tag, and for IE you can set the text property of the script tag to the JS text, in all other browsers you should be able to append a text node with the contents to script tag. If there's any code that expects a script tag to actually contain the src location of the file, this won't work, but it should be fine for most situations.