I am making a javascript function that adds script and css elements into my head section, but I need to run that before the page is loaded, how could I do that?
you can run script after DOM tree is loaded not images and sounds etc just DOM
document.addEventListener("DOMContentLoaded", function(event) {
console.log("DOM fully loaded and parsed");
});
Your best bet is to send just the script in your html and then have it bootstrap the rest of the page:
<html>
<head>
<script>
// do whatever you're trying to do with your code
$.get('path/to/page/partial.html').done(handleNewPartial);
</script>
</head>
<html>
The reason you can't do it the way you're asking is that your code is always included as a DOM element on the page, ie it has to be delivered inside a <script> tag to be used by the browser. So by definition your script can not be used until after your html has been parsed into the DOM.
Hope this helps!
I think I figured out my issue.
The issue was that it was loading the scripts, but it wasn't running their window.onload. When I made the function run staticly instead of a window.onload, it works fine. Thanks for the help!
EDIT: This also works to dynamically load the CSS stylesheets, so YAY
Related
There are many good practices with document loaded:
$(function(){
....
}
The code above seems to wait for some extra resources to be loaded to run. At least I am quite sure it's waiting for the Google Adsense content to be loaded.
But what about the </body> loaded? Because sometimes there's no need to wait for the document loaded. I just want to immediately work on the DOM that is loaded. Is there any event can do that?
Update:
The code is like this:
<script>
// The script tag has to be above the a tag - which will be worked on later.
</script>
<a id="tobeworkedon">test</a>
</body>
I can't just move the script tag to the latter part. Can I still make it as fast as it were right before the </body> tag?
$(function(){
....
}
This method offers a way to run JavaScript code as soon as the page's DOM becomes safe to manipulate.
Simply if the browser supports, you can use
document.addEventListener('DOMContentLoaded', func, false);
For older browsers, you can try
document.attachEvent("onreadystatechange", func);
Maybe is this what you looking:
<body onload="myFunction()"></body>
But notice: It will fire uppon body loading, even if some images or resources are not loaded yet.
In JavaScript, when I want to run a script once when the page has loaded, should I use window.onload or just write the script?
For example, if I want to have a pop-up, should I write (directly inside the <script> tag):
alert("hello!");
Or:
window.onload = function() {
alert("hello!");
}
Both appear to run just after the page is loaded. What is the the difference?
The other answers all seem out of date
First off, putting scripts at the top and using window.onload is an anti-pattern. It's left over from IE days at best or mis-understandings of JavaScript and the browser at worst.
You can just move your scripts the the bottom of your html
<html>
<head>
<title>My Page</title>
</head>
<body>
content
<script src="some-external.js"></script>
<script>
some in page code
</script>
</body>
</html>
The only reason people used window.onload is because they mistakenly believed scripts needed to go in the head section. Because things are executed in order if your script was in the head section then the body and your content didn't yet exist by definition of execute in order.
The hacky workaround was to use window.onload to wait for the rest of the page to load. Moving your script to the bottom also solved that issue and now there's no need to use window.onload since your body and content will have already been loaded.
The more modern solution is to use the defer tag on your scripts but to use that your scripts need to all be external.
<head>
<script src="some-external.js" defer></script>
<script src="some-other-external.js" defer></script>
</head>
This has the advantage that the browser will start downloading the scripts immediately and it will execute them in the order specified but it will wait to execute them until after the page has loaded, no need for window.onload or the better but still unneeded window.addEventListener('load', ...
window.onload just runs when the browser gets to it.
window.addEventListener waits for the window to be loaded before running it.
In general you should do the second, but you should attach an event listener to it instead of defining the function. For example:
window.addEventListener('load',
function() {
alert('hello!');
}, false);
Here's the documentation on MDN.
According to it:
The load event fires at the end of the document loading process. At this point, all of the objects in the document are in the DOM, and all the images and sub-frames have finished loading.
Your first snippet of code will run as soon as browser hit this spot in HTML.
The second snippet will trigger popup when the DOM and all images are fully loaded (see the specs).
Considering the alert() function, it doesn't really matter at which point it will run (it doesn't depend on anything besides window object). But if you want to manipulate the DOM - you should definitely wait for it to properly load.
That depends on if you want it to run when the script element is encountered or if you want it to run when the load event fires (which is after the entire document (including such things as images) has loaded).
Neither is always right.
In general, however, I'd avoid assigning functions directly to onload in favour of using addEventListener (with compatibility libraries if I needed to support older browsers).
The reason for waiting for the DOM to be loaded is so that you can target any elements that load after your script. If you're just creating an alert, it doesn't matter. Let's say, however, you were targeting a div that was in your markup after your script, you would get an error if you don't wait until that piece of the DOM tree to load.
document.ready is a great alternative to window.onload if you're using jQuery.
See here: window.onload vs $(document).ready()
You have three alternatives:
Directly inside the script tag runs it as soon as it is parsed.
Inside document.addEventListener( "DOMContentLoaded", function(){}); will run it once the DOM is ready.
Inside window.onload function(){}) will run as soon as all page resources are loaded.
I'm using a JavaScript upload script that says to run the initialize function as soon as the DOM is ready. I currently have it working just fine with either a call to the function with body.onload or directly after the function is defined. The function builds some HTML in a placeholder div that acts as the file uploader tool.
My question is what is the best practice here? Since it works for now, why would the instructions say to run the init function as soon as the DOM is ready? Should I be adding a <script> tag directly after the placeholder DIV for example?
<script>
window.addEventListener("DOMContentLoaded", function() {
// do stuff
}, false);
</script>
You do that so you know all the parsed elements are available in the DOM etc.
The easiest solution is using jQuery and its $(document).ready(function() { .... }); function. Instead of .... you put your own code.
Note that it basically does the same thing #Shadow2531 suggested, but also works in old browsers not supporting that event.
The DOM is usually ready before onLoad runs. onLoad only runs after everything loads - external scripts, images, stylesheets, etc.
But the DOM, i.e. the HTML structure is ready before that. If you run the code at the bottom of the page (or after the parts of the page the script works with) that will work fine as well.
In 2015 you have two options with modern browsers:
document.onload
this fires when the document is loaded, but other resources (most notably images) have not necessarily finished loading.
window.onload
this fires when the document is loaded, AND all other resources (again, most notably images) are loaded.
Both of the above events would be better utilized with window.addEventListener() of course, as multiple listeners would be allowed.
You could also just move the <script> to the bottom of your page like this:
<html>
<body>
<main></main>
<script>
// code
</script>
</body>
</html>
As you probably know you should not run init functions before the DOM is fully loaded.
The reason you must run the init function as soon as the DOM is ready, is that once the page has loaded the user starts hitting buttons etc. You have to minimize the small inavoidable gap where the page is loaded and the init-functions haven't run yet. If this gap gets too big (ie. too long time) your user might experience inappropiate behaviour... (ie. your upload will not work).
Other users have provided fine examples of how to call the init function, so I will not repeat it here... ;)
Get jQuery and use the following code.
$(document).ready(function(){
// Do stuff
});
var Tette =
{
init: function()
{
/* Your HTML code */
}
};
Core.start(Tette);
You can try in this code, registering "Core.start(your object)" on the last line of the script. This is a way to load in safety your functions after the DOM loading.
I am trying to run my javascript in my asp.net webform page but I am not sure it runs properly because all the elements are not loaded yet. How can I make sure my script is at the very bottom of the page with using jquery? So it can run when the page is loaded?
Even though everyone says use $(document).ready it's kind of an anti-pattern.
What you really want to do is put any scripts you want to load at the end of the body
<html>
<head> ... </head>
<body>
...
<script src="..." ></script>
</html>
As long as your scripts are at the end of all your other HTML content the javascript will only fire when the content above it has loaded.
With pure JavaScript, you can use
window.onload = function() {
// Page loaded
};
Or you can use jQuery's ready function:
$( document ).ready( function() {
// Dom loaded
} );
Note: jQuery's ready function fires when the DOM has loaded (unless the browser does not support a dom-ready method), not when the whole page has loaded (images, scripts, etc).
Use .ready():
$(document).ready(function($) {
// page is loaded
});
While JavaScript provides the load event for executing code when a
page is rendered, this event does not get triggered until all assets
such as images have been completely received. In most cases, the
script can be run as soon as the DOM hierarchy has been fully
constructed. The handler passed to .ready() is guaranteed to be
executed after the DOM is ready, so this is usually the best place to
attach all other event handlers and run other jQuery code. When using
scripts that rely on the value of CSS style properties, it's important
to reference external stylesheets or embed style elements before
referencing the scripts.
With jQuery, you want to attach to the ready event. This gets fired when all DOM elements have been loaded:
jQuery(document).ready(function(){
// jQuery Code here
});
Shorthand version:
$(function(){
// ...
});
Using this method, I usually put my jQuery in an external file, or in the <head> tag.
You should put your code inside the document ready block as suggested in the JQuery documentation.
This way it will be loaded when all the scripts will be loaded.
$(document).ready(function(){
//Put your code here
});
What is the best way to make sure javascript is running when page is fully loaded?
If you mean "fully loaded" literally, i.e., all images and other resources downloaded, then you have to use an onload handler, e.g.:
window.onload = function() {
// Everything has loaded, so put your code here
};
If you mean "after all of the HTML has been parsed and all elements are accessible from script", at which point images may still be downloading, then you can either put your script at the bottom of the source HTML or use a document.ready handler. Or both. Refer to any of the other answers for details.
i would like to load jquery.js after the window.onload event has been fired by browser (reducing load time)
Doing that maybe with appendChild the problem is i can't use anymore $(document).ready();
Is there a way to use something equivalent to .ready after the loading of jQuery (after the window.onload?)
thanks
Just place <script>s at the bottom of your HTML files. If you load jQuery right before the closing </body> tag, page rendering isn’t blocked while jQuery is loading.
It doesn’t matter if you speed up window.onload if you’re not gonna use it anyway. E.g. if you use…
$(document).ready(function() {
// …
});
…or its shorter alias…
$(function() {
// …
});
…internally it’s not relying on window.onload, but on DOMContentLoaded.
Loading scripts at the bottom is gonna help you much more than waiting for window.onload to start loading your scripts.
I think you can't. In order to use jquery as well as other plugins that developed from jquery, you have to load jquery.js first of all. (in the part, you have to put the script that load jquery.js on top)
It doesn't even work if you load (Slider, Thickbox, DatePicker...) first then jquery.js
^^
first of all load jquery from here
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js">
loading it from google means the user most likley already has it cached resulting in a much quicker load.
also to be honest jquery isnt that big a file (less than a meg) so it shouldnt really affect load times.
all script tags should be at the bottom of your page in anycase.. so loading times wont be affected.
content
script tags
otherwise you could do something like
if ($.jquery){
document.body. and then my js gets rusty... but basicaly append the script tag