I'm executing an external script, using a <script> inside <head>.
Now since the script executes before the page has loaded, I can't access the <body>, among other things. I'd like to execute some JavaScript after the document has been "loaded" (HTML fully downloaded and in-RAM). Are there any events that I can hook onto when my script executes, that will get triggered on page load?
These solutions will work:
As mentioned in comments use defer:
<script src="deferMe.js" defer></script>
or
<body onload="script();">
or
document.onload = function ...
or even
window.onload = function ...
Note that the last option is a better way to go since it is unobstrusive and is considered more standard.
Triggering scripts in the right moment
A quick overview on how to load / run the script at the moment in which they intend to be loaded / executed.
Using "defer"
<script src="script.js" defer></script>
Using defer will trigger after domInteractive (document.readyState = "interactive") and just before "DOMContentLoaded" Event is triggered. If you need to execute the script after all resources (images, scripts) are loaded use "load" event or target one of the document.readyState states. Read further down for more information about those events / states, as well as async and defer attributes corresponding to script fetching and execution timing.
This Boolean attribute is set to indicate to a browser that the script
is meant to be executed after the document has been parsed, but before
firing DOMContentLoaded.
Scripts with the defer attribute will prevent the DOMContentLoaded
event from firing until the script has loaded and finished evaluating.
Resource: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script#attributes
* See the images at the bottom for feather explanation.
Event Listeners - Keep in mind that loading of the page has more, than one event:
"DOMContentLoaded"
This event is fired when the initial HTML document has been completely loaded and parsed, without waiting for style sheets, images, and subframes to finish loading. At this stage you could programmatically optimize loading of images and CSS based on user device or bandwidth speed.
Executes after DOM is loaded (before images and CSS):
document.addEventListener("DOMContentLoaded", function(){
//....
});
Note: Synchronous JavaScript pauses parsing of the DOM.
If you want the DOM to get parsed as fast as possible after the user requested the page, you could turn your JavaScript asynchronous and optimize loading of style sheets
"load"
A very different event, **load**, should only be used to detect a *fully-loaded page*. It is an incredibly popular mistake to use load where DOMContentLoaded would be much more appropriate, so be cautious.
Executes after everything is loaded and parsed:
document.addEventListener("load", function(){
// ....
});
MDN Resources:
https://developer.mozilla.org/en-US/docs/Web/Events/DOMContentLoaded
https://developer.mozilla.org/en-US/docs/Web/Events/load
MDN list of all events:
https://developer.mozilla.org/en-US/docs/Web/Events
Event Listeners with readyStates - Alternative solution (readystatechange):
You can also track document.readystatechange states to trigger script execution.
// Place in header (do not use async or defer)
document.addEventListener('readystatechange', event => {
switch (document.readyState) {
case "loading":
console.log("document.readyState: ", document.readyState,
`- The document is still loading.`
);
break;
case "interactive":
console.log("document.readyState: ", document.readyState,
`- The document has finished loading DOM. `,
`- "DOMContentLoaded" event`
);
break;
case "complete":
console.log("document.readyState: ", document.readyState,
`- The page DOM with Sub-resources are now fully loaded. `,
`- "load" event`
);
break;
}
});
MDN Resources: https://developer.mozilla.org/en-US/docs/Web/API/Document/readyState
Where to place your script (with & without async/defer)?
This is also very important to know where to place your script and how it positions in HTML as well as parameters like defer and async will affects script fetching, execution and HTML blocking.
* On the image below the yellow label “Ready” indicates the moment of ending loading HTML DOM. Then it fires: document.readyState = "interactive" >>> defered scripts >>> DOMContentLoaded event (it's sequential);
If your script uses async or defer read this: https://flaviocopes.com/javascript-async-defer/
And if all of the above points are still to early...
What if you need your script to run after other scripts are run, including those scheduled to run at the very end (e.g. those scheduled for the "load" event)? See Run JavaScript after all window.onload scripts have completed?
What if you need to make sure your script runs after some other script, regardless of when it is run? This answer to the above question has that covered too.
Reasonably portable, non-framework way of having your script set a function to run at load time:
if(window.attachEvent) {
window.attachEvent('onload', yourFunctionName);
} else {
if(window.onload) {
var curronload = window.onload;
var newonload = function(evt) {
curronload(evt);
yourFunctionName(evt);
};
window.onload = newonload;
} else {
window.onload = yourFunctionName;
}
}
You can put a "onload" attribute inside the body
...<body onload="myFunction()">...
Or if you are using jQuery, you can do
$(document).ready(function(){ /*code here*/ })
or
$(window).load(function(){ /*code here*/ })
I hope it answer your question.
Note that the $(window).load will execute after the document is rendered on your page.
If the scripts are loaded within the <head> of the document, then it's possible use the defer attribute in script tag.
Example:
<script src="demo_defer.js" defer></script>
From https://developer.mozilla.org:
defer
This Boolean attribute is set to indicate to a browser that the script
is meant to be executed after the document has been parsed, but before
firing DOMContentLoaded.
This attribute must not be used if the src
attribute is absent (i.e. for inline scripts), in this case it would
have no effect.
To achieve a similar effect for dynamically inserted scripts use
async=false instead. Scripts with the defer attribute will execute in
the order in which they appear in the document.
Here's a script based on deferred js loading after the page is loaded,
<script type="text/javascript">
function downloadJSAtOnload() {
var element = document.createElement("script");
element.src = "deferredfunctions.js";
document.body.appendChild(element);
}
if (window.addEventListener)
window.addEventListener("load", downloadJSAtOnload, false);
else if (window.attachEvent)
window.attachEvent("onload", downloadJSAtOnload);
else window.onload = downloadJSAtOnload;
</script>
Where do I place this?
Paste code in your HTML just before the </body> tag (near the bottom of your HTML file).
What does it do?
This code says wait for the entire document to load, then load the
external file deferredfunctions.js.
Here's an example of the above code - Defer Rendering of JS
I wrote this based on defered loading of javascript pagespeed google concept and also sourced from this article Defer loading javascript
Look at hooking document.onload or in jQuery $(document).load(...).
JavaScript
document.addEventListener('readystatechange', event => {
// When HTML/DOM elements are ready:
if (event.target.readyState === "interactive") { //does same as: ..addEventListener("DOMContentLoaded"..
alert("hi 1");
}
// When window loaded ( external resources are loaded too- `css`,`src`, etc...)
if (event.target.readyState === "complete") {
alert("hi 2");
}
});
same for jQuery:
$(document).ready(function() { //same as: $(function() {
alert("hi 1");
});
$(window).load(function() {
alert("hi 2");
});
NOTE: - Don't use the below markup ( because it overwrites other same-kind declarations ) :
document.onreadystatechange = ...
I find sometimes on more complex pages that not all the elements have loaded by the time window.onload is fired. If that's the case, add setTimeout before your function to delay is a moment. It's not elegant but it's a simple hack that renders well.
window.onload = function(){ doSomethingCool(); };
becomes...
window.onload = function(){ setTimeout( function(){ doSomethingCool(); }, 1000); };
<script type="text/javascript">
function downloadJSAtOnload() {
var element = document.createElement("script");
element.src = "defer.js";
document.body.appendChild(element);
}
if (window.addEventListener)
window.addEventListener("load", downloadJSAtOnload, false);
else if (window.attachEvent)
window.attachEvent("onload", downloadJSAtOnload);
else window.onload = downloadJSAtOnload;
</script>
http://www.feedthebot.com/pagespeed/defer-loading-javascript.html
Working Fiddle on <body onload="myFunction()">
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript">
function myFunction(){
alert("Page is loaded");
}
</script>
</head>
<body onload="myFunction()">
<h1>Hello World!</h1>
</body>
</html>
If you are using jQuery,
$(function() {...});
is equivalent to
$(document).ready(function () { })
or another short hand:
$().ready(function () { })
See What event does JQuery $function() fire on? and https://api.jquery.com/ready/
document.onreadystatechange = function(){
if(document.readyState === 'complete'){
/*code here*/
}
}
look here: http://msdn.microsoft.com/en-us/library/ie/ms536957(v=vs.85).aspx
Just define <body onload="aFunction()"> that will be called after the page has been loaded. Your code in the script is than enclosed by aFunction() { }.
<body onload="myFunction()">
This code works well.
But window.onload method has various dependencies. So it may not work all the time.
Comparison
In below snippet I collect choosen methods and show their sequence. Remarks
the document.onload (X) is not supported by any modern browser (event is never fired)
if you use <body onload="bodyOnLoad()"> (F) and at the same time window.onload (E) then only first one will be executed (because it override second one)
event handler given in <body onload="..."> (F) is wrapped by additional onload function
document.onreadystatechange (D) not override document .addEventListener('readystatechange'...) (C) probably cecasue onXYZevent-like methods are independent than addEventListener queues (which allows add multiple listeners). Probably nothing happens between execution this two handlers.
all scripts write their timestamp in console - but scripts which also have access to div write their timestamps also in body (click "Full Page" link after script execution to see it).
solutions readystatechange (C,D) are executed multiple times by browser but for different document states:
loading - the document is loading (no fired in snippet)
interactive - the document is parsed, fired before DOMContentLoaded
complete - the document and resources are loaded, fired before body/window onload
<html>
<head>
<script>
// solution A
console.log(`[timestamp: ${Date.now()}] A: Head script`);
// solution B
document.addEventListener("DOMContentLoaded", () => {
print(`[timestamp: ${Date.now()}] B: DOMContentLoaded`);
});
// solution C
document.addEventListener('readystatechange', () => {
print(`[timestamp: ${Date.now()}] C: ReadyState: ${document.readyState}`);
});
// solution D
document.onreadystatechange = s=> {print(`[timestamp: ${Date.now()}] D: document.onreadystatechange ReadyState: ${document.readyState}`)};
// solution E (never executed)
window.onload = () => {
print(`E: <body onload="..."> override this handler`);
};
// solution F
function bodyOnLoad() {
print(`[timestamp: ${Date.now()}] F: <body onload='...'>`);
infoAboutOnLoad(); // additional info
}
// solution X
document.onload = () => {print(`document.onload is never fired`)};
// HELPERS
function print(txt) {
console.log(txt);
if(mydiv) mydiv.innerHTML += txt.replace('<','<').replace('>','>') + '<br>';
}
function infoAboutOnLoad() {
console.log("window.onload (after override):", (''+document.body.onload).replace(/\s+/g,' '));
console.log(`body.onload==window.onload --> ${document.body.onload==window.onload}`);
}
console.log("window.onload (before override):", (''+document.body.onload).replace(/\s+/g,' '));
</script>
</head>
<body onload="bodyOnLoad()">
<div id="mydiv"></div>
<!-- this script must te at the bottom of <body> -->
<script>
// solution G
print(`[timestamp: ${Date.now()}] G: <body> bottom script`);
</script>
</body>
</html>
There is a very good documentation on How to detect if document has loaded using Javascript or Jquery.
Using the native Javascript this can be achieved
if (document.readyState === "complete") {
init();
}
This can also be done inside the interval
var interval = setInterval(function() {
if(document.readyState === 'complete') {
clearInterval(interval);
init();
}
}, 100);
Eg By Mozilla
switch (document.readyState) {
case "loading":
// The document is still loading.
break;
case "interactive":
// The document has finished loading. We can now access the DOM elements.
var span = document.createElement("span");
span.textContent = "A <span> element.";
document.body.appendChild(span);
break;
case "complete":
// The page is fully loaded.
console.log("Page is loaded completely");
break;
}
Using Jquery
To check only if DOM is ready
// A $( document ).ready() block.
$( document ).ready(function() {
console.log( "ready!" );
});
To check if all resources are loaded use window.load
$( window ).load(function() {
console.log( "window loaded" );
});
Use this code with jQuery library, this would work perfectly fine.
$(window).bind("load", function() {
// your javascript event
});
$(window).on("load", function(){ ... });
.ready() works best for me.
$(document).ready(function(){ ... });
.load() will work, but it won't wait till the page is loaded.
jQuery(window).load(function () { ... });
Doesn't work for me, breaks the next-to inline script. I am also using jQuery 3.2.1 along with some other jQuery forks.
To hide my websites loading overlay, I use the following:
<script>
$(window).on("load", function(){
$('.loading-page').delay(3000).fadeOut(250);
});
</script>
You can write a function on a specific script file and call it in to your body element using onload attribute.
Exemple:
<script>
afterPageLoad() {
//your code here
}
</script>
Now call your script into your html page using script tag:
<script src="afterload.js"></script>
into your body element; add onload attribute like this:
<body onload="afterPageLoad();">
As Daniel says, you could use document.onload.
The various javascript frameworks hwoever (jQuery, Mootools, etc.) use a custom event 'domready', which I guess must be more effective. If you're developing with javascript, I'd highly recommend exploiting a framework, they massively increase your productivity.
Using the YUI library (I love it):
YAHOO.util.Event.onDOMReady(function(){
//your code
});
Portable and beautiful! However, if you don't use YUI for other stuff (see its doc) I would say that it's not worth to use it.
N.B. : to use this code you need to import 2 scripts
<script type="text/javascript" src="http://yui.yahooapis.com/2.7.0/build/yahoo/yahoo-min.js" ></script>
<script type="text/javascript" src="http://yui.yahooapis.com/2.7.0/build/event/event-min.js" ></script>
i can catch page load by this code
<script>
console.log("logger saber");
window.onload = (event) => {
console.log('page is fully loaded');
document.getElementById("tafahomNameId_78ec7c44-beab-40de-9326-095f474519f4_$LookupField").value = 1;;
};
</script>
My advise use asnyc attribute for script tag thats help you to load the external scripts after page load
<script type="text/javascript" src="a.js" async></script>
<script type="text/javascript" src="b.js" async></script>
<script type="text/javascript">
$(window).bind("load", function() {
// your javascript event here
});
</script>
I have a script that dynamically loads jQuery, by inserting it in <head> element:
// pseudo code
headElelement.insertBefore(script, firstChild);
However, immediately after that call, I start to use jQuery, but at that moment it is undefined. How is that possible ?
That's because jQuery is not fully loaded yet. You may need to execute your jQuery code only after jQuery has been loaded by attaching an event handler to the onload event of your dynamically created script element as shown below.
script.onload = function() {
// Put your jQuery code here.
console.log(jQuery);
};
Cross-Browser solution for supporting older browsers like IE8 and below:
script.onload = script.onreadystatechange = function(event) {
event = event || window.event;
if (event.type === "load" || (/loaded|complete/.test(script.readyState))) {
script.onload = script.onreadystatechange = null;
// Put your jQuery code here.
console.log(jQuery);
}
};
If you would post your relevant code it would be easier ;-) but anyways, this is one possible way of doing it:
<html>
<head>
<script type="text/javascript" src="path_to_js/jquery.js"></script>
<script type="text/javascript" src="path_to_js/your_js_code.js"></script>
...
</head>...
and in the file your_js_code.js you'll have:
... /* All your modules and functions here */
/* DOM loading ready */
$(document).ready(function () {
call_your_methods_here();
});
By the way, it is usually better to load your JS files at the very end of the <body> in the HTML, that way your HTML starts displaying first and the user "sees" your page faster, while the JS code is still loading.
I'm using joomla site, and Forced to use extra java script.
My Question is:
How to force loading the javascript ONLY after page complete
I dont mean DELAY them, But make them in Queue till the page complete loading.
I tried many of links tutorial but nothing helps me.
Please,
Would you provide correct example in order to make me understand.
Example to JS file I inserted to buttom of my page:
<script src="/js/easing.js" type="text/javascript"></script>
Can you provide Jquery code to force all those script to wait till the page load complete?
Thank you
Tariq
Ales Kotnik answer's in great, and also if you want to do it in your own specifiec time, you can do something like that:
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);
}
this will load a script only when you call it, and then you activate it like this:
<script type="text/javascript" src="http://your.cdn.com/first.js"></script>
<script type="text/javascript">
loadScript("http://your.cdn.com/second.js", function(){
//initialization code
});
</script>
Use <script src="..." async="async"/>. In modern browsers (HTML5)it will spawn fetching javascript files separately and won't delay loading of your HTML. You can just put script tags at the end of your <body>.
All of my JavaScript files are already at the bottom but Google Page Speed is giving this suggestion to improve speed:
Defer parsing of JavaScript
88.6KiB of JavaScript is parsed during initial page load. Defer
parsing JavaScript to reduce blocking of page rendering.
http://ajax.googleapis.com/ajax/libs/jquery/1.5.1/jquery.min.js
(76.8KiB) http://websiteurl/js/plugins.js (11.7KiB) http://websiteurl/
(109B of inline JavaScript)
This is the my html (example)
<html>
<head>
<!--[if lt IE 9]><script src="//html5shim.googlecode.com/svn/trunk/html5.js"></script><![endif]-->
<head>
<body>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.5.1/jquery.min.js"></script>
<script>!window.jQuery && document.write(unescape('%3Cscript src="js/libs/jquery-1.5.1.min.js"%3E%3C/script%3E'))</script>
<script src="js/plugins.js"></script>
<script>$(document).ready(function() {
$("#various2").fancybox({
'width': 485,
'height': 691,
});
});</script>
</body>
</html>
What should I do to increase performance by using defer?
Is it only for Google chrome or for all?
If you're looking for page performance then first and foremost you should move those scripts to the bottom of your page to allow the other assets to load.
Also use dns prefetch in the head to set the base domain for google-code
<link rel="dns-prefetch" href="//ajax.googleapis.com">
Since this is just a small piece of code, you could simply add it to your plugins.js file at the bottom then defer the plugins file.
<script src="js/plugins.js" defer></script>
That's what I'd do anyway, all my sites are optimized to 98 and 97 respectively in yslow and page speed.
Hope it helps.
-V
Add in <script type="text/javascript" defer="defer"> tag like that it works for me.
<script type="text/javascript" defer="defer" src="<?php echo $this->getSkinUrl();?>js/jquery.bxslider.js"></script>
I see this is an old question, but since I was looking for a good answer myself, I am going to share the method I currently use.
As far as inline Javascript is concerned, what I do is change all the type attributes to text/deferred-javascript, or something similar, so that the code within the script tag is not evaluated during page load. Then I attach a function to the page onload event; said function finds all the scripts matching the type above and evaluates the code inside using eval(). I know in general eval() is evil but it seems to be helpful here.
For external Javascript files, I do something very similar. Instead of adding the script tags to the page, I record them and insert them one-by-one after page load has completed.
One problem I'm having is that if one of the inline deferred Javascript contains an error (say a parse error), the subsequent scripts are not loaded (but that might depend on my current implementation).
That's probably a generic response/suggestion for when it encounters a certain level of performance.
Although, it specifically mentions jQuery, a plugin, and 109 bytes of inline JavaScript. Do you have any inline JavaScript? Are you also placing your JavaScript includes at the bottom of the <body>?
Example
Loading Performance article
EDIT:
Based on recently posted HTML...
As a test, remove these two items to see if it makes any difference:
<!--[if lt IE 9]><script src="//html5shim.googlecode.com/svn/trunk/html5.js"></script><![endif]-->
<script>!window.jQuery && document.write(unescape('%3Cscript src="js/libs/jquery-1.5.1.min.js"%3E%3C/script%3E'))</script>
Also, the warning message mentions 109 bytes of inline JS, yet I don't see anything like that in the HTML you've posted.
Hi recently we have created an opensource nodejs framework called "elegant framework" that help you building fast web application and we succeeded to get 100% google page speed in both desktop and mobile in all pages :
you can check it at:
https://developers.google.com/speed/pagespeed/insights/?url=getelegant.com
there is a lot of things you can learn from it by viewing the page source also if anything you cannot understand please comment so i can help you with
so far you can try this method:
// Load script element as a child of the body
function loadJS(src, 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;
if (callback) {
callback();
}
}
};
} else { //Others
script.onload = function () {
if (callback) {
callback();
}
};
}
script.src = src;
document.body.appendChild(script);
}
// Load style element as a child of the body
function loadCSS(href,callback) {
var element = document.createElement("link");
element.rel = "stylesheet";
if (element.readyState) { //IE
element.onreadystatechange = function () {
if (element.readyState == "loaded" || script.readyState == "complete") {
element.onreadystatechange = null;
if (callback) {
callback();
}
}
};
} else { //Others
element.onload = function () {
if (callback) {
callback();
}
};
}
element.href = href;
document.body.appendChild(element);
}
// Load All Resources
function loadResources() {
// css
loadCSS("/compressed/code-mirror-style.css?please1");
loadCSS("/compressed/all.css?please2");
// js
loadJS("/compressed/code-mirror.js", function () {
loadJS("/compressed/common.js", function () {
$("[data-lang]").each(function () {
var code = $(this).addClass("code").text();
$(this).empty();
var myCodeMirror = CodeMirror(this, {
value: code,
mode: $(this).attr("data-lang"),
lineNumbers: !$(this).hasClass('inline') && !$(this).hasClass('no-numbers'),
readOnly: true
});
});
});
});
}
// Check for browser support of event handling capability
if (window.addEventListener) {
window.addEventListener("load", loadResources, false);
} else if (window.attachEvent) {
window.attachEvent("onload", loadResources);
} else {
window.onload = loadResources
}
Is it possible to load certain scripts like
<script type="text/javascript" src="somescript.js"></script>
when the rest of the page has loaded?
Imagine I have a few larger script files like this that are not needed when the page is loaded. E.g. I'm using the Google Maps API that is only used when a button is clicked (so not on page load).
Is it possible to load the rest of the page first, before processing all those script tags in my head?
In JQuery you could do this on document ready
$.getScript("somescript.js", function(){
alert("Script loaded and executed.");
});
simply you can add into that script file defer parameter
<script src="pathToJs" defer></script>
you can check this question as well
It is possible. I was doing a similar thing in an AJAX intensive site, but I was loading the Google Charts API. Here is the code I used to load the Google Charts API when a button was clicked on the page.
function loadGoogleChartsAPI() {
var script = document.createElement("script");
// This script has a callback function that will run when the script has
// finished loading.
script.src = "http://www.google.com/jsapi?callback=loadGraphs";
script.type = "text/javascript";
document.getElementsByTagName("head")[0].appendChild(script);
}
function loadGraphs() {
// Add callback function here.
}
This uses a callback function that will run when the script has loaded.
No one mentioned these?
$(window).load(function(){
// do something
});
or
$(window).bind("load", function() {
// do something
});
$(document).ready(function() {
var ss = document.createElement("script");
ss.src = "somescript.js";
ss.type = "text/javascript";
document.getElementsByTagName("head")[0].appendChild(ss);
});
Please see my code. The onload event will occur when the script has finished loading. Or the onerror event will occur.
function loadJavaScript() {
var script = document.createElement("script");
script.src = "javaScript.js";
script.type = "text/javascript";
script.onload = function () {
console.log('script was loaded successfully');
}
script.onerror = function (e) {
console.error('script.onerror');
}
document.getElementsByTagName("head")[0].appendChild(script);
}
Thanks to answer.
Also see my code of the load of the script.
use the getScript method of jquery! or try simply to put this script on the end of the page?
Yes, this is possible by dynamically injecting the JavaScript files from code. There are lots of libraries which you can use:RequireJS, HeadJS etc. Recently I found this document which compares lots of JavaScript loader libraries.
To just allow the page to show before your script is loaded, use the async attribute:
<script src="//url/to/script.js" async></script>
To hide the loading spinner in the browser, append the script tag after the page finished loading:
<script>
document.addEventListener('DOMContentLoaded', function() {
var script = document.createElement('script');
script.src = '//url/to/script.js';
document.getElementsByTagName('body')[0].appendChild(script);
});
</script>
Yep, that's completely possible. Add an onLoad="foo();" event to your <body> tag and have it invoke your scripts. You'll need to wrap your external JS in a function and do something like:
//EXTERNAL JS (jsstuff.js)
function Mojo() {
document.getElementById('snacks').style.visibility = "visible";
alert("we are victorious!");
}
//YOUR HTML
<html>
<head>
<script type='text/javascript'></script>
</head>
<body onLoad='Mojo();'>
<div id='snacks'>
<img src='bigdarnimage.png'>
</div>
</body>
</html>