Are there downsides to loading javascript or CSS via server-side conditionals?

Question

Let's say I have a javascript or CSS file that is only used on one or very few pages on a site. I also have a method for easily identifying when those pages are served, such as a human-readable URL. Is it bad practice to conditionally serve the JS using a server-side test to see if the script is necessary? With PHP for example, I might do this:

<?php
if($page='myFancyPage')
{
?>
    <script src="myFancyScipt.js"></script>
<?php
}
?>

I'm not losing the benefits of browser caching am I? Are there are other reasons why I shouldn't do this?

I recognize that is might get unwieldy as a site gets large and more and more conditionals have to be piled up. But aside from that issue, are there reasons to avoid this practice?

Given how much talk there is about the need to combine one's scripts or css into a single file (to reduce server requests), I'm wondering what people think of this technique as an alternative? Combining can be quite a pain (especially when you add scripts later that only have limited use/scope on a site). — technoTarek
– technoTarek, Commented May 15, 2012 at 18:20
You're still ahead combining considering that the combined css or js file is about the size of the average JPG. For small files the request is the bottleneck, not the payload. — Diodeus - James MacFarlane
– Diodeus - James MacFarlane, Commented May 15, 2012 at 18:25

Diodeus - James MacFarlane · Accepted Answer · 2012-05-15 18:14:57Z

4

No because the condition is on the SERVER not the CLIENT.

The client has no idea why it got the file, but when it gets it, it will be cached.

answered May 15, 2012 at 18:14

Diodeus - James MacFarlane

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2 Comments

Andy Davies Over a year ago

The overhead of the extra response/request is a downside

raddrick Over a year ago

@AndyDavies that was my comment, but I was down voted with no reason.. +1 to you good sir.

Jeff Lambert · Accepted Answer · 2012-05-15 18:16:12Z

1

Browser caching happens on the client side (the browser), whereas your PHP will execute on the server side. If your browser sees a page that has included myFancyScript.js in it, then all subsequent requests to that page will use the cached version of myFancyScript.js, assuming the response headers from the server allow it and the browser obeys the headers.

answered May 15, 2012 at 18:16

Jeff Lambert

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Comments

raddrick · Accepted Answer · 2012-05-15 19:12:22Z

0

you are not loosing the benefits of file caching, unless they're needed and not served up! file caching will only benefit you if the file hasn't changed and is already present on the client.

there is a benefit to selectively linking to your external files (only linking files that this page needs), because your file will load faster since it wont have to parse the excess js/css...you're better off only adding files that will be needed by the page

edited May 15, 2012 at 19:12

answered May 15, 2012 at 18:16

raddrick

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Comments

Andy Davies · Accepted Answer · 2012-05-18 16:15:47Z

0

It depends...

Generally the advice is to minimise the number of requests a page makes for external resources, as often the overhead of the extra request/response is greater than if the source of the file had been merged into another.

This is why the standard performance recommendation is to merge JS files together to create the minimum number of downloads

answered May 18, 2012 at 16:15

Andy Davies

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