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Another approach would be to put all the scripts in the and add defer attributes to the non-essential scripts. However, I read that older versions of Firefox don’t pick up the defer attribute.
I think that’s a perfectly acceptable approach. I read somewhere that defer doesn’t work on a lot of browsers, but I could be hopelessly wrong.
I suppose it’s all about taste. I personally add them before the body tag (in the head) and also add small snippets where needed inside the page.
website performance rule : put all css in the beginning(head) and put all javascript in the end of the page.
I think a lot of developers run JavaScript just before the so that it is run after all the elements have been rendered.
However, if you organise your code correctly, the position on the page doesn’t matter.
For example, when using jQuery, you can ensure the code isn’t run until the page and its elements are fully rendered by doing the following:
Then the script reference can be put in the head tag.
Script tags should be referenced just before . This prevents render blocking while the scripts load and is much better for site perception speed.
No obtrusive JavaScript should be used when using this technique.
Don’t forget, content loads faster when you move scripts to the bottom. Assuming that ajax isn’t being used to load the pages default content.
Position is extremely important, even when using DOMReady . A lot of developers put javascript tags just before the because all scripts are loaded and executed synchronously. When they are in the , the page rendering stops to download → parse → execute each script.
(Piling on. ) The primary reason for putting SCRIPTs at the bottom of the page is less about making sure the DOM is loaded (albeit an important reason) and more about making the page appear RESPONSIVE. If you load scripts at the top of the page the browser downloads them first and your content waits until they’re downloaded — this can make the page APPEAR to load slower, making users unhappy.
But what happens if the user starts playing with the page. Suppose I’ve an AJAX dropdown which will start loading after the page has appeared to the user but while it is loading, the user clicks it! And what if a ‘really impatient’ user submits the form?
JavaScript code should be placed at the end of the document so that it doesn’t delay the parallel loading of page elements. This does then require that the JavaScript code is written in a specific way, but it does improve the speed of page loads.
Also, ideally you could host references like this under a different (sub)domain. References to jQuery should be pointed to Google’s CDN too.
One of the reasons you’d want to put scripts before the is if they manipulate the DOM without user interaction, so you’ll need the DOM to be loaded in order to be manipulated. Another way to do that is to add an event listener and run the scripts when the page has loaded, but this will require additional code, which might get complicated if you have a lot of scripts, especially ones you haven’t written yourself. Putting them at the end of the page also will speed up page load, though in the case of DOM manipulating scripts you might get some not-so-pretty results from that.
I’d say that’s perfectly sensible. As you said, as long as you don’t move essential scripts (e.g. jQuery, Modernizr, etc., etc.) out from the , you shouldn’t have problems.
Moving non-essential scripts to the bottom of the page should help with the perceived loading speed (that and minimizing / concatenating scripts).
It all depends on what you mean by «essential for UX». I agree with having Modernizr appear early for example, but not everything needs to load straight away. If you’re trying to avoid a flash of unstyled text (FOUT), that’s a good reason. Similarly, if you have scripts that affect how the page looks before the user does anything, you should load those early.
Don’t forget though, speed is part of UX. There’s no advantage in having some jQuery interaction ready to run when the user can’t see the content it applies to yet. The difference between loading the scripts at the start of the end is a matter of seconds. If you let the page load first, the user will be using those seconds to take the page in, allowing you to load scripts unobtrusively.
Your page will load faster if you move scripts to the bottom of the page, and that makes a difference to your pagerank these days.
Also, some versions of Internet Explorer will throw errors if you try to run a script before the element it refers to has loaded.
Like Ed says, your scripts should be stored in a separate file, and in as few files as possible.
In HTML, JavaScript code is inserted between tags.
Old JavaScript examples may use a type attribute: .
The type attribute is not required. JavaScript is the default scripting language in HTML.
A JavaScript function is a block of JavaScript code, that can be executed when «called» for.
For example, a function can be called when an event occurs, like when the user clicks a button.
You will learn much more about functions and events in later chapters.
JavaScript in or
You can place any number of scripts in an HTML document.
Scripts can be placed in the , or in the section of an HTML page, or in both.
JavaScript in
In this example, a JavaScript function is placed in the section of an HTML page.
The function is invoked (called) when a button is clicked:
JavaScript in
In this example, a JavaScript function is placed in the section of an HTML page.
The function is invoked (called) when a button is clicked:
Placing scripts at the bottom of the element improves the display speed, because script interpretation slows down the display.
Scripts can also be placed in external files:
External scripts are practical when the same code is used in many different web pages.
JavaScript files have the file extension .js.
To use an external script, put the name of the script file in the src (source) attribute of a tag:
You can place an external script reference in or as you like.
The script will behave as if it was located exactly where the tag is located.
External scripts cannot contain tags.
Placing scripts in external files has some advantages:
To add several script files to one page — use several script tags:
An external script can be referenced in 3 different ways:
This example uses a full URL to link to myScript.js:
This example uses a file path to link to myScript.js:
This example uses no path to link to myScript.js:
You can read more about file paths in the chapter HTML File Paths.
thanks for helping me! Sorry if I worded this wrong or caused you extra time. I have a set of code, in fact, it is a piece of javascript I learned on W3Schools. The code creates a simple slideshow for my Art. Here is the W3Schools Link I don’t like having my javascript code all over my HTML and typically I solve simple issues by using onload events so that all my javascript can stay in the head. I’m still new and genuinely appreciate any insight you have. I want to learn, not have you do it for me. This is my script, currently, I have to place it at the end of the body tags for it to work. When I place this into an external js file and link that file in the head, it fails as I would expect. My problem is I don’t know how to solve placing complex code (i.e more than one function) into the head. Normally on single functions, which is all I have needed so far, I would attach an onload event to that function. Can someone show me how it is possible to place this set of script in an external file and link it in the head tags? Here is my website, I have left it broken in case you want to see the console log errors. The slideshow is down the page halfway and on page load it shows all three images in the slideshow. When you click the left and right arrows it will change and look normal.
Scripts to be executed when they are called, or when an event is triggered, are placed in functions.
Put your functions in the head section, this way they are all in one place, and they do not interfere with page content.
If your is not placed inside a function, or if your script writes page content, it should be placed in the body section. It is a good idea to place scripts at the bottom of the element. This can improve page load, because script compilation can slow down the display.
In short and simple language:
tags are loaded and executed by the browser as and when it encounters them. Most modern browsers have a number of multiple threads that render the HTML page at the same time, however, if all those threads are blocked waiting to load JavaScript assets, the page takes a whole lot longer to render.
That’s the reason people usually place their tags in the at the bottom of the page, so that all the HTML of the page has been rendered, and the user can see something while the page loads any heavy JavaScript assets.
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