ASP.Net & Javascript: <head> element - javascript

I remember my instructor last semester mentioning something about how to sequence JavaScript commands in the HEAD section of my ASP.Net document, but for the life of me, I can't find it in my notes. Are there special concerns about the order Java and other statements inthe HEAD section?
I am putting the Javascript on a .aspx page that is based on a Master Page, if that makes any difference.
Thanks in advance!

No, the sequence doesn't really matter. And you don't need to put your JS in the HEAD section either, unless you're referencing an external JS file. If you're using master pages, and you need a certain JS function on a page, just create the JS function on the page, with the requisite script tags:
ASPX:
<script language="javascript" type="text/javascript">
someFunction = function(){
//do something
}
</script>

Related

HTML / jQuery: How to properly include external jQuery file

I am new to JS and programming in general and hope someone can help me with this.
I am currently working on building a website where every page has its separate HTML / PHP file.
jQuery and my global / general JS functions are included in the footer of all these pages through a separate includes file "footer.php".
So far everything works as intended.
Now I have some pages that will use specific jQuery functions so I want to load the corresponding JS only if such a page is loaded.
To do this I saved the corresponding codes in separate JS files (e.g. nameOfExternalJsFile.js) and wrapped everything in there in the following:
$(document).ready(function(){
// ...
});
I then made the following updates to the corresponding PHP pages (example):
<head>
<?php
require_once("includes/header.php");
?>
<!-- here I want to include the specific jQuery functions -->
<script src="includes/js/nameOfExternalJsFile.js"></script>
</head>
<!-- ... -->
<!-- here I include the main JS functions -->
<?php require_once("includes/footer.php"); ?>
I have two concerns with this:
I am not sure if this is the right way of including such files since
I need to have them available on document ready.
I include my main JS in the footer since I was told this improves
performance but can I then include jQuery functions in the header at all ?
Can someone let me know if this is correct or if I should change anything here ?
Many thanks for any help with this.
Wrapping the functions in $(document).ready automatically takes care of this concern. From the JQuery documentation on document.ready.
A page can't be manipulated safely until the document is "ready."
jQuery detects this state of readiness for you. Code included inside
$( document ).ready() will only run once the page Document Object
Model (DOM) is ready for JavaScript code to execute.
Technically it doesn't matter whether you include the scripts in the header or the footer, as long you load JQuery first and your script second.
That said, it's generally recommended that both scripts go just before the closing body tag to increase performance as you suggested. There are some articles that discuss this like this post from performance expert Steve Souders and this guide from the Yahoo! Exceptional Performance team.
You should load the $(document).ready(...) stuff only after you have loaded jQuery, that is, in the footer file, after the jQuery <script> tag, like this :
<script src="includes/js/jQuery.min.js"></script>
<script src="includes/js/nameOfExternalJsFile.js"></script>
It`s good practise to locate all the JS files in the end of the body
<html>
<head></head>
<body>
... Some HTML
<script>SomeScripts</script>
</body>
</html>
</pre>
If you want to be sure that your external scripts are loaded after page load use:
$(function(){
/* Your code from the scripts */
});
You can change the content of footer.php to include /nameOfExternalJsFile.js manually at the bottom of the page. That´s the safest way to do it because you may load jquery before loading others scripts.

How to include an external javascript file when using ExtJs?

I'm using ExtJs 4.2.2 and included all necessary js and css files, and my codes work just fine, ONLY IF I write my code into script tags within my html file. When I try to put these code into another file with .js extension and include it between head tags properly, it returns nothing. I'm sure I've included my js file properly because when I fill it with standard js codes, I get results. But with ExtJS syntax, the same code which return results within script tags, returns nothing. How? Do I miss something?
The following two are equivalent. If one works, the others work, too, regardless of what js code you use:
(Ex 1.)
<html><head>
<script>//your js code here</script>
</head><body>
</body></html>
and
(Ex 2.)
<html><head>
<script src="jscode.js"></script>
</head><body>
</body></html>
where jscode.js contains
// your js code here
Furthermore, the following two are equivalent:
(Ex 3.)
<html><head>
</head><body>
<script>//your js code here</script>
</body></html>
and
(Ex 4.)
<html><head>
</head><body>
<script src="jscode.js"></script>
</body></html>
NOTHING will change in behaviour.
I think (but you didnt post ANY code at all, so it's jsut guessing) that you had Example 3 working, but changed to Example 2. But only 3 and 4 are equivalent! And now you call that ExtJS fault!
You are executing code in an onLoad event or a Load event, perhaps like:
$(window).load(function() {
$('p').css('');
})
Remove this section and use only this in the javascript file and include it in a <Head> section:
$('p').css('');
When you are coding in html, then it execute steps one by one. But when we use a separate file then it executes it slower than HTML code.
I think I can use those technique mentioned on the top.
I am sure it will work.

asp.net 2.0 site and location of <script/> tags causing problems/conflicting

I have no idea how to describe this accurately/intelligently because it seems to be completely impossible, yet there must some reason for it.
I am trying to leverage jquery, jquery-ui, qtip (tooltip for jquery) and highcharts (javascript charting), but for purpose of post I could just as easily been only using jQuery and jQuery-UI.
If I include my <script/> tags at the bottom of my <head/> element I get an error trying to call the .slider() extension to configure my sliders. But if I put the <script/> tags right before the closing of my <body/> element then everything works. To illustrate, the following will not work (obviously some pseudo code below):
<head>
<script jquery.js/>
<script jquery-ui.js/>
</head>
<body>
... html ...
<script type="text/javascript">
$(document).ready(function () {
$(".slider").slider( { .. options .. } );
} )
</script>
... more html *including* the .slider elements
</body>
However, if I move the two jQuery script tags to be right above the </body> closing element things work. When the script tags are in the head element and I debug my application, basically the page does appear to have completely loaded and Visual Studio highlights the line calling the .slider() function saying it doesn't know what slider() is. Looking at the call stack, it appears to be correctly calling it from the document ready function...the mark up all appears to be there as well, making me believe the document truly is ready.
Now I didn't include things that are required by asp.net 1.1/2.0 site in my pseudo code, namely a <form/> element with runat="server' and the use of a <asp:ScriptManager/> tag (we needed that for parsing monetary values from different cultures leveraging Microsoft Ajax). I can't believe they would be causing the problem, but maybe they are. Additionally, asp.net injects several of its own script sections (i.e. for validation, post back, etc.)
Regarding the form tag...all the html and document.ready markup would be inside the form tag, while the script tags are always outside of the form tag (either above it, in the head or below it at the bottom of the body).
Obviously I could leave the script tags at the bottom, and I very well may end up doing that, but I am trying to get a clean 'template site' of which to use when creating new client sites and it just feels wrong that I have a restriction forcing me to put those tags at the bottom of the html. I'm sure our framework code (or maybe asp.net's) is simply inserting something that is causing problems/conflicts with jQuery, but I don't really know how to go about debugging/diagnosing what that problem is. So if anyone has any suggestions I'd greatly appreciate it.
It looks like jQuery 1.3.2 is being loaded by ASP.NET (see your second WebResource.axd). The two library versions are overwriting each other. Thus the reason it works when you load 1.6.2 at the end of the page.

Including client-side scripts in head in ASP.NET

Hey guys. I don't do HTML or Javascript, I prefer to work in C#, but one of the JS guys tells me that he needs a script included within the head tag. The page in question is a content page of a master page. I can't seem to make this work. I tried adding the script by a programmatic reference this.ClientScript.RegisterClientScriptInclude, but it came out in the <body> tag. I tried adding a ScriptManager and a ScriptReference in the contentplaceholder inside the <head> tag of the master page, but this didn't work either. How can this be accomplished?
Just put a client side reference to the script in.
<head> <script lang="Javascript" src="./scripts/yourscript.js"></script>
Or, if it needs to be inline, include the actual script right there in the master page.

Where should JS scripts go in an HTML file?

If you have JS code which is intended to run as part of loading/building the page, where in the HTML should this go? For instance modifying a <div> or adding some links.
Should this be put in the <body>, interspersed with HTML? Or should it be between the <head> and <body> elements? What order do things happen in - the order they are in the page or does HTML all happen before (non-<head>) JS is run?
If you have JS code which is intended to run as part of loading/building the page, where in the HTML should this go?
Just before the closing </body> tag is emerging as the best practice barring a specific requirement for it to be elsewhere (which there can sometimes be). It's the recommendation of the YUI folks, for instance, but it's not just them.
What order do things happen in - the order they are in the page or does HTML all happen before (non-) JS is run?
When a script tag is encountered, unless you use the defer or async attribute (and the browser supports them), all HTML parsing comes to a screeching halt and the script is downloaded and handed to the JavaScript interpreter. When the JavaScript interpreter finishes processing the script, the HTML parser can continue. It has to do this because the JavaScript can insert tokens into the HTML stream via document.write. This is also why you can load a script file and then load a second script file that relies on the first, and know that they'll get loaded in the right order. It's also why you can't access elements that are further down in the HTML stream from a script higher up in it unless you defer your code somehow (window.onload or the "DOM loaded" events many libraries support, such as jQuery's ready or Prototype's dom:loaded).
An upshot of this is that the typical practice of putting script tags in the head actually slows down the apparent load time of the page, unless those script tags need to be there for some reason. Hence the recommendation to put them just before the closing </body> tag.
There's a "gotcha" you have to watch for, though: If you have parts of the page that you want to respond to with JavaScript if the user has it enabled, loading your script at the very end leaves a brief but real race condition lying around: The user can interact with the page while your script is being downloaded. There are a variety of ways of handling that. My favorite is to detect whether JavaScript is enabled with inline script (not a separate file) in the head element and, if so, to put in a document-level handler for things where possible (you can do this with click events, for instance) which basically queues up or disables the click during that very brief period of time. That way, if JavaScript is enabled, you'll avoid the race condition, but if it isn't, any unobtrusive fallback you have in place will work.
The whole HTML file is executed in the order it is written, that means
<html>
<div id="ID"></div>
<script type="text/javascript">
document.getElementById('ID').innerHTML = "HELLO";
</script>
</html>
changes the contents of the div, wherease
<html>
<script type="text/javascript">
document.getElementById('ID').innerHTML = "HELLO";
</script>
<div id="ID"></div>
</html>
does not, because the JS code is executed before the div has loaded.
EDIT: If you want the JS to run after the page has loaded use window.onload or document.body.onload or
<body onload="...">
Alternatively if you're using a JS library such as jQuery, you can use
$(document).ready(function() {
...
});
Put them as functions in its own .js file which you include by <script src> at end of HTML <head> or <body>. If any of them needs to be executed during document load, call it using window.onload or whatever load function the JS library/framework offers, if you are using any.
As to the exact location, putting them in end of <head> allows them to be downloaded before the HTML page is been shown in browser and putting them in end of <body> allows the page to be shown a tad sooner because downloading the scripts will block the page rendering, thus it's a better speed experience.
However, IMO, it's a bit more robust to have the scripts downloaded before the page is rendered whenever you have some page elements which cannot be used without JS. In case of an impatient user this would otherwise lead to unusable elements.
I'd put it in a separate .js file and wrap the code so it is executed after the DOM is loaded. If you use a framework like jQuery or Prototype this should be easy.
For best performance place your JavaScript files at the BOTTOM of the HTML page you are serving.
To ensure that everything is set when you try to use it, execute only after the DOM is ready (there are multiple variations of this, my advice: Use a JavaScript Library).
You can put a script tag in the head, body, between the two, and more. You can put it most places but see this for a more in depth look.

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