I have senerio, where I need to render my HTML page by using dynamic JavaScript.
I am using loadScript function to load external JavaScript and passing callback funtion. In my HTML page , I am loading this script for my header.
My header section is working perfectly after the script is loaded and I my head section I can see my new script.
However , when I am trying to use the variables from this script its undefined.
function loadScript(url,callback){
var script = document.createElement("script");
script.type = "text/javascript";
script.id="acvDataRequest";
document.getElementsByTagName("head")[0].appendChild(script);
if (script.readyState){ //IE
script.onreadystatechange = function(){
if (script.readyState == "loaded" ||
script.readyState == "complete"){
script.onreadystatechange = null;
callback();
}
};
} else { //Others
script.onload = function(){
alert(dataHeader) // I CAN SEE MY OBJECT FROM LOADED SCRIPT
callback();
};
}
script.src = url;
alert(dataHeader); // IT SAYS UNDEFINED
}
calling a script using :
var actionName ="JSONdata/json.js";
loadScript(actionName,mergeTemplateJSONScript);
Please advice , why i can't see my variables even if my script is there.
Inside script.onload , I am able to see my variable but not outside
The line script.src = url; triggers the loading of the script file. If you call alert immediately after it your external script has not been loaded yet. You can only access variables from the json once the onreadystatechange or onload functions have been called.
What you should do is using it like this:
var actionName ="JSONdata/json.js";
loadScript(actionName,function(){
alert(dataHeader);
});
What you assign:
script.src = url;
that just starts the loading of the dynamic script. When you call the second alert() on the very next line your script has not yet loaded (it is loading in the background at that point). You can only reliably access the variables from the newly loaded script from within the onload handler or in some function called from the onload handler.
Keep in mind that the dynamic loading of scripts is asynchronous. That means it happens in the background while other scripts keep running (thus your second alert() runs before the script has finished). And, then the script finishes loading some time later and when it does the onload handler is called.
So, when you dynamically load scripts, all code that uses those scripts needs to either be in the onload handler, in some function called from the onload handler or guarenteed not to execute until some time later (such as in an event handler that you're sure won't happen before the script finishes loading).
To explain further, I've added some annotations to your code:
function loadScript(url,callback){
var script = document.createElement("script");
script.type = "text/javascript";
script.id="acvDataRequest";
document.getElementsByTagName("head")[0].appendChild(script);
if (script.readyState){ //IE
script.onreadystatechange = function(){
if (script.readyState == "loaded" ||
script.readyState == "complete"){
script.onreadystatechange = null;
callback();
}
};
} else { //Others
script.onload = function(){
// ** your script is now loaded here **
alert(dataHeader) // I CAN SEE MY OBJECT FROM LOADED SCRIPT
callback();
};
}
script.src = url;
// ** your script is in the process of loading here and has likely not completed **
alert(dataHeader); // IT SAYS UNDEFINED
}
Related
is there any way to load jQuery file if it's not present without using document.write
<script>
window.jQuery || document.write('<script src="/path/to/your/jquery"><\/script>');
</script>
this way is good but it has major issue because if the visitor has slow connection the browser will prevent it from executing
when it happen I get this warning
file is invoked via document.write. The network request for this script MAY
be blocked by the browser in this or a future page load due to poor
network connectivity
I tried many solutions but nothing worked
You can pass a load callback to the IFFE that will be executed when the script loads or invoked immediately if jQuery exists.
var load = function(){
// your jQuery code goes here
$('#hello').html('jQuery Loaded');
};
(function(window, loadCallback){
if(!window.jQuery){
var script = document.createElement("script");
script.type = "text/javascript";
script.src = "https://code.jquery.com/jquery-3.3.1.min.js";
script.onload = loadCallback;
document.head.appendChild(script);
}else{
loadCallback();
}
})(window, load);
<div id="hello"></div>
I'm loading multiple javascript references dynamically with appending script tag to DOM.
I would appreciate your help with explaining script loading behavior.
What i'm assuming is that when i append script element to DOM, script is downloaded and then executed. But when .onload event is fired? As soon as script starts execution or when it finishes execution? If second is true, how to await for script to be executed/initialized (i would like to execute callback that will append additional html with scripts that depends dynamically loaded references )?
To load scripts i use function of below:
function recursiveInclude(scriptPathArray, callback) {
if (scriptPathArray.length > 0) {
var scriptPath = scriptPathArray[0];
// check if script is already loaded if not load
// this_loadedScriptList is one scope level up variable
if (this_loadedScriptList.indexOf(scriptPath) > 0 == false) {
var body = document.getElementsByTagName('body')[0];
var scriptElement = document.createElement('script');
scriptElement.type = 'text/javascript';
scriptElement.src = scriptPath;
// first script from the array will loaded as soon as body.appendChild function will be called
// when script loads 'onload' event will fire next script loading
// to this work properly first script from scriptPathArray has to be removed:
scriptPathArray.shift();
// if there are any other scripts to load, load them sequentially
if (scriptPathArray.length > 0) {
// then bind the event to the callback function
// there are several events for cross browser compatibility
// script.onreadystatechange = callback;
scriptElement.onload = recursiveInclude(scriptPathArray, callback);
} else {
// if no other scripts to load - fire base callback;
scriptElement.onload = callback;
}
// fire the loading
body.appendChild(scriptElement);
// add script to loaded array.
this_loadedScriptList.push(scriptPath);
}
}
}
there is a big issue you must know about. Doing that implies that you remotely load the code. Modern web browsers will load the file and keep executing your current script because they load everything asynchronously to improve performance. (This applies to both the jQuery method and the manual dynamic script loading method.)
It means that if you use these tricks directly, you won't be able to use your newly loaded code the next line after you asked it to be loaded, because it will be still loading.
Practically all you can do is to use an event to run a callback function when the script is loaded.
function loadScript(url, callback)
{
var head = document.getElementsByTagName('head')[0];
var script = document.createElement('script');
script.type = 'text/javascript';
script.src = url;
script.onreadystatechange = callback;
script.onload = callback;
// Fire the loading
head.appendChild(script);
}
Then write your code like this:
var myCode = function() {
...
};
At last you can run it:
loadScript("the-remote-script.js", myCode);
JavaScript is neither threaded nor event-interrupted. The hole script is executed before anything else can happen. Events are captured until the browser gets back the control. So onload or any other event can only be fired before or after the script execution is done. Actually onload is fired after the execution.
There is an event beforescriptexecute still supported by firefox, however, it has been remove from HTML5.1 specs.
You can try it out yourself:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<script>
console.log('base script start');
var script=document.createElement('script');
script.onload = function() { console.log('onload fired'); }
// MDN says:
// This event was a proposal in an early version of the specification. Do not rely on it.
//
script.addEventListener('beforescriptexecute', function () { console.log('beforescriptexecute fired'); });
script.src = 'external.js';
document.head.appendChild(script);
console.log('waiting 3 seconds');
timebase = Date.now();
while((Date.now() - timebase) < 3000)
;
console.log("base script end");
</script>
</body>
</html>
external.js:
console.log('external start... waiting 3 seconds');
timeext = Date.now();
while((Date.now() - timeext) < 3000)
;
console.log('external end');
base script start
waiting 3 seconds
base script end
beforescriptexecute fired
external start... waiting 3 seconds
external end
onload fired
MDN - beforescriptexecute
I am using jQuery to load a script from Mapquest within the cordova onDeviceReady function. However, half the time the script does not load properly and the functions cannot be used.
$.ajax({
url: "http://www.mapquestapi.com/sdk/leaflet/v2.s/mq-geocoding.js?key=sv99PLA3H8jGWSa1a097UKewBWrNWLWN",
dataType: 'script',
success: function(){alert('hello')},
async: false
});
Is there anything that I can change to ensure that the script is always loaded properly? The script is always able to alert('hello'), but even then, the functions will not always work properly.
You can load the script dynamically without the $.getScript function as the following does:
function loadScript ( src, callback )
{
var script = document.createElement ( 'script' );
script.type = 'text/javascript';
script.async = true;
script.onerror = function ( err )
{
throw new URIError('The script ' + err.target.src + ' is not accessible.');
}
if(callback && typeof callback == 'function')
script.onload = callback;
document.head.appendChild(script);
script.src = src;
}
What it does is:
Creates a <script> element;
Tells the browser that it should be loaded asynchronously so it doesn't interrupts the rest of the resources while they load;
Uses the onerror and onload events to provide feedback on the script loading;
Appends the script to the <head> and sets the src making it actually load.
In your case, you'd use it like this:
loadScript ( "http://www.mapquestapi.com/sdk/leaflet/v2.s/mq-geocoding.js?key=sv99PLA3H8jGWSa1a097UKewBWrNWLWN", function ( )
{
alert(1);
} );
Compatibility
Keep in mind that the async attribute does not works on all browsers: http://caniuse.com/#feat=script-async
This question already has answers here:
'onload' handler for 'script' tag in internet explorer
(2 answers)
Closed 7 years ago.
I know my subject is quite tricky but i dont know how to much more ellaborate it on the subject alone.
so here how it goes.
i have a button
Load IT!
on the script tag:
function loadTheFile() {
var script = $("<script><\/script>");
script.attr("type", "text/javascript");
script.attr('src','http://www.thisismyexternalloadingjsfile"');
$('body').append(script);
alert("done! the file has been loaded");
}
the script well, when loaded will automatically have a modal box.
but the problem is, my alert seems to fire first than what is one the script
so how will i know if i have finished to load the script?
update for the first attempt to answer:
function loadTheFile() {
var script = $("<script><\/script>");
script.attr("type", "text/javascript");
script.attr('src','http://www.thisismyexternalloadingjsfile"');
$('body').append(script);
$(document).ready(function() {
alert("done! the file has been loaded")};
}
same problem
alert does indeed run before the script has been loaded. All that appending the script tag to the page does is append the script tag to the page. Then the browser has to download the script and, once received, run it. That will be after your loadTheFile function has exited.
So you need to get a callback when the script has actually be loaded and run. This is more standard than it used to be, but still has some cross-browser hassles. Fortunately for you, jQuery's already solved this problem for you (since you're using jQuery already):
function loadTheFile() {
$.getScript('http://www.thisismyexternalloadingjsfile"')
.then(function() {
alert("done! the file has been loaded");
});
}
Re your comment:
but my script file has data-* attributes
Assuming you're talking about data-* attributes on the script tag, then you'll have to do a bit more work, but it's still fairly straightfoward:
function loadTheFile() {
var load = $.Deferred();
var script = document.createElement('script');
script.src = 'http://www.thisismyexternalloadingjsfile"';
// No need for `type`, JavaScript is the default
script.setAttribute("data-foo", "bar");
script.onreadystatechange = function() {
if (script.readyState === "loaded") {
load.resolve();
}
};
script.onload = function() {
load.resolve();
};
load.then(function() {
alert("done! the file has been loaded");
});
document.body.appendChild(script); ;// Or wherever you want to put it
}
The onreadystatechange bit is to handle older versions of IE.
Rather than forge the script with text and jQuery, just use native Javascript:
var s = document.createElement('script');
s.onload = scriptLoaded;
s.src = '/path/to/my.js';
document.body.appendChild(s);
function scriptLoaded() {
console.log('Script is loaded');
}
Try something along these lines:
Your main page:
function whenScriptIsReady(){
alert('This function is called when the other script is loaded in!')
}
function loadTheFile() {
var script = $("<script><\/script>");
script.attr("type", "text/javascript");
script.attr('src','myotherjs.js');
$('body').append(script);
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
Load IT!
myotherjs.js:
alert('This will automatically run when the JS is loaded in!');
whenScriptIsReady();
JavaScript is executed asynchronously, so you alert will be executed before the browser can load the new script. If you want to execute logic after the script has been loaded, you could add an event listener to your script that will call the function 'loadFunc` once the script load is completed:
var loadFunc = function() {
alert("External Javascript File has been loaded");
};
//Other browsers trigger this one
if (script.addEventListener)
script.addEventListener('load', loadFunc, false);
I just want to inject jQuery into a webpage from a safari extension. But only to some pages because adding jQuery as a start-/endscript would inject it to all pages and this makes browsing slow.
I tried it by creating a script tag using its onload function:
var node = document.createElement('script');
node.onload = function(){
initjquerycheck(function($) {
dosomethingusingjQuery($);
});
};
node.async = "async";
node.type = "text/javascript";
node.src = "https://code.jquery.com/jquery-2.0.3.min.js";
document.getElementsByTagName('head')[0].appendChild(node);
to check if jquery is loaded i use:
initjquerycheck: function(callback) {
if(typeof(jQuery) != 'undefined'){
callback(jQuery);
}else {
window.setTimeout(function() { initjquerycheck(callback); }, 100);
}
}
But typeof(jQuery) remains undefined. (checked that using console.log()).
Only if I call console.log(typeof(jQuery)) from the debugging console it returns 'function'. Any ideas how to fix that? Thanks in advance!
Extension injected scripts cannot access the web page's JavaScript namespace. Your injected script creates a <script> element and adds it to the page's DOM, but then the jQuery object instantiated by the script belongs to the page's namespace, not to your injected script's.
There are at least two potential solutions. One, inject jQuery into the page the normal way, using the extension API. This method is only viable if the web pages that you are targeting can be categorized using URL patterns.
Two, use Window.postMessage to communicate between your injected script and the web page's namespace. You will need to add another <script> to the page, and in this script, have a listener for the message event. The listener will be able to use jQuery as if it were "native" to the page itself.
Here's some code to get you started, if needed.
In the extension injected script:
var s0 = document.createElement('script');
s0.type = 'text/javascript';
s0.src = 'https://code.jquery.com/jquery-2.0.3.min.js';
document.head.appendChild(s0);
var s1 = document.createElement('script');
s1.type = 'text/javascript';
s1.src = safari.extension.baseURI + 'bridge.js';
document.head.appendChild(s1);
window.addEventListener('message', function (e) {
if (e.origin != window.location.origin)
return;
console.log(e.data);
}, false);
window.postMessage('What jQuery version?', window.location.origin);
In bridge.js:
window.addEventListener('message', function (e) {
if (e.origin != window.location.origin)
return;
if (e.data == 'What jQuery version?') {
e.source.postMessage('Version ' + $.fn.jquery, window.location.origin);
}
}, false);