What benefits come from dynamically loading and unloading JavaScript and CSS stylesheets?

Question

What benefits come from dynamically loading and unloading JavaScript and CSS stylesheets?

Introduction:

Currently, I am in the process of developing a website that will utilize ajax to change content without refreshing the main frame and images every time. The main frame has its own site.css stylesheet.

Query 1:

Considering the use of a single stylesheet for all style information, would it be practical for website modularity? Updating the CSS every time a new page or content is added/removed due to varying style requirements might be a concern.

Query 1.1:

The same query, but now in relation to Javascript.

Query 2:

If having multiple stylesheets is deemed beneficial, is unloading a stylesheet when not in use advantageous? For instance, loading profile.php would dynamically load profile.css, but upon switching to settings.php, unloading profile.css and loading settings.css might have performance implications or save website size.

Query 2.1

Similar to the previous question, but now focusing on javascript functions.

javascript html css ajax

Answer 1

Answer №1

After your javascript or css file has been successfully downloaded to the user's machine, it gets cached by their browser. This means there is no need for another HTTP request, saving on additional costs. While lazy loading scripts and stylesheets can be a good idea, there is no point in unloading these web assets once they have already been delivered to the client.

It is beneficial to implement a mechanism to compile your scripts and stylesheets to reduce the initial number of http requests to just one per asset type. While having only one stylesheet and javascript file may seem like a daunting architectural challenge in some cases, it is still possible to present it to the browser in this way. As a user of .NET, I am unfamiliar with how this would be handled in PHP, but I am confident that the necessary functionality exists.

Answer 2

After your javascript or css file has been successfully downloaded to the user's machine, it gets cached by their browser. This means there is no need for another HTTP request, saving on additional costs. While lazy loading scripts and stylesheets can be a good idea, there is no point in unloading these web assets once they have already been delivered to the client.

It is beneficial to implement a mechanism to compile your scripts and stylesheets to reduce the initial number of http requests to just one per asset type. While having only one stylesheet and javascript file may seem like a daunting architectural challenge in some cases, it is still possible to present it to the browser in this way. As a user of .NET, I am unfamiliar with how this would be handled in PHP, but I am confident that the necessary functionality exists.

Answer 3

Answer №2

Solution:

Striking the right balance is key. Utilize multiple CSS and JS files during development, but consolidate them into one each for deployment. Tools are available to assist with this process, eliminating the need to work with one large file.

The challenge lies in determining which CSS and JS code is used frequently across your site and should be included on every page. For code that is only utilized on specific pages, consider dynamically loading it, unless your site is very small. Finding the perfect balance is crucial.

Additional Points:

It is not beneficial to unload CSS and JS files once they have been loaded and cached on the user's machine. The effort is futile as the files remain accessible for future use.

Answer 4

Solution:

Striking the right balance is key. Utilize multiple CSS and JS files during development, but consolidate them into one each for deployment. Tools are available to assist with this process, eliminating the need to work with one large file.

The challenge lies in determining which CSS and JS code is used frequently across your site and should be included on every page. For code that is only utilized on specific pages, consider dynamically loading it, unless your site is very small. Finding the perfect balance is crucial.

Additional Points:

It is not beneficial to unload CSS and JS files once they have been loaded and cached on the user's machine. The effort is futile as the files remain accessible for future use.

Answer 5

Answer №3

This seems like a case of premature optimization in my opinion. Let's examine the loading times on SO:

all.css - 46.8 Kb - loaded in 87 ms

To emphasize this further, here are the loading times for various elements on this specific SO page (tested on my four-year-old laptop with a fiber optic connection):

Additionally, here are the sizes of (some of) these components relative to each other:

My conclusion is that if you focus on building the foundation of your site effectively, you shouldn't need to stress over optimizing those last few milliseconds unless they are truly crucial.

Answer 6

This seems like a case of premature optimization in my opinion. Let's examine the loading times on SO:

all.css - 46.8 Kb - loaded in 87 ms

To emphasize this further, here are the loading times for various elements on this specific SO page (tested on my four-year-old laptop with a fiber optic connection):

Additionally, here are the sizes of (some of) these components relative to each other:

My conclusion is that if you focus on building the foundation of your site effectively, you shouldn't need to stress over optimizing those last few milliseconds unless they are truly crucial.

Answer 7

Answer №4

When your browser needs to load additional CSS or JS files, it sends a request for each one. This means that the more requests your page has to make, the longer it will take to load.

Answer 8

When your browser needs to load additional CSS or JS files, it sends a request for each one. This means that the more requests your page has to make, the longer it will take to load.

Answer 9

Answer №5

Question 1

Absolutely, because once the CSS is downloaded, it gets cached. It's a good practice to avoid defining style info inline and instead use a simple PHP script to declare the content type as CSS and include your individual CSS files as one, like this:

header("content-type: text/css");
$file = file_get_contents('your.css');
$file .= file_get_contents(...)

Then just reference it normally in a link tag:

<link rel="stylesheet" href="yourCSS.php" >

Question 1.1

Same answer as before, just use this code snippet:

header("content-type: application/javascript");

Question 2

No, once loaded, the content will always be accessible in the memory cache. Google's GWT framework compiles all external content into a large bundle because of the limitation on concurrent HTTP requests per domain. That's why Yahoo's speed guide suggests placing CSS at the top of the page and JavaScript at the bottom of the body tag.

Question 2.1

No, but it's advisable to keep external files small and always minify production code.

Answer 10

Question 1

Absolutely, because once the CSS is downloaded, it gets cached. It's a good practice to avoid defining style info inline and instead use a simple PHP script to declare the content type as CSS and include your individual CSS files as one, like this:

header("content-type: text/css");
$file = file_get_contents('your.css');
$file .= file_get_contents(...)

Then just reference it normally in a link tag:

<link rel="stylesheet" href="yourCSS.php" >

Question 1.1

Same answer as before, just use this code snippet:

header("content-type: application/javascript");

Question 2

No, once loaded, the content will always be accessible in the memory cache. Google's GWT framework compiles all external content into a large bundle because of the limitation on concurrent HTTP requests per domain. That's why Yahoo's speed guide suggests placing CSS at the top of the page and JavaScript at the bottom of the body tag.

Question 2.1

No, but it's advisable to keep external files small and always minify production code.

Answer 11

Answer №6

Response 1

While there may be advantages to loading CSS rules on an as-needed basis, I would caution against it. It is important to maintain a consistent layout for your website or web application. Your design should be uniform across all pages, even if you are loading additional modules through Ajax requests. Take JQuery UI, for example; whether you utilize a widget or not, its style is still downloaded.

However, if you require specific styles for the HTML snippets retrieved from your requests, you can include these rules within a <style> tag in the <head> section, or add the CSS file to the <head>, or even apply the styles directly to the style attribute of your HTML elements.

Response 1.1

If you do choose to load Javascript code as needed, ensure that it is not loaded multiple times, unless absolutely necessary for certain circumstances...

In any case, neither CSS nor Javascript should be "unloaded" as there is no benefit to that.

Response 2 and 2.1

A few years ago, the answer to whether loading a single stylesheet and/or Javascript was better would likely have been affirmative. However, with advancements in internet speed and computer performance, browsers have become very efficient and the potential performance gain is often not worth the hassle. Additionally, if these resources are static (with unchanged URLs), they are cached and reused efficiently. Users generally do not mind waiting when expected (refer to section 2.10), particularly if it is their first time visiting.

Answer 12

Response 1

While there may be advantages to loading CSS rules on an as-needed basis, I would caution against it. It is important to maintain a consistent layout for your website or web application. Your design should be uniform across all pages, even if you are loading additional modules through Ajax requests. Take JQuery UI, for example; whether you utilize a widget or not, its style is still downloaded.

However, if you require specific styles for the HTML snippets retrieved from your requests, you can include these rules within a <style> tag in the <head> section, or add the CSS file to the <head>, or even apply the styles directly to the style attribute of your HTML elements.

Response 1.1

If you do choose to load Javascript code as needed, ensure that it is not loaded multiple times, unless absolutely necessary for certain circumstances...

In any case, neither CSS nor Javascript should be "unloaded" as there is no benefit to that.

Response 2 and 2.1

A few years ago, the answer to whether loading a single stylesheet and/or Javascript was better would likely have been affirmative. However, with advancements in internet speed and computer performance, browsers have become very efficient and the potential performance gain is often not worth the hassle. Additionally, if these resources are static (with unchanged URLs), they are cached and reused efficiently. Users generally do not mind waiting when expected (refer to section 2.10), particularly if it is their first time visiting.

What benefits come from dynamically loading and unloading JavaScript and CSS stylesheets?

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

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