When Chrome clears disk cache? - javascript

I have one website which serves listener.js on the main page. I want to update this javascript file with some extra codes. But browsers (especially chrome) has memory and disk cache. Also HTTP cache of course. I tried something about that state. I tried just F5, the file loaded from memory cache. Then I killed chrome and opened the website again, javascript file loaded from the disk cache. So I have 2 questions;
When chrome clears disk cache?
How can I say to my visitors don't use any cache and get the new javascript file from my server?
Update:
Can I do this with no-cache Http header?

Removing temporarily cached file known as cache busting. It is useful because browser doesn't have to download these files again.
If it is causing issues, developers can force browsers to download new files. This is performed by re-naming file but there is a better way
src="js/listener.js" => src="js/listener.js?v=2"
Update:
Or hash like this => ?v=c298c7f8233d which is better than ?v=2 (comment by Tech Guy)
(Credits: 30-seconds)

Chrome doesn't auto clear disk cache unless this option is checked
Privacy settings > Content settings > Keep local data only until you quit browser
In which case, it deletes cache on closing the browser.
You usually prevent a client from saving your files in cache by hashing your filenames in
each build, which is the most common cache-busting technique. That means in every release, you will have a new file name and the old cached file won't matter. For instance
Most build tools like Webpack have cache-busting features that you can turn on.
You don't want to stop the user from caching at all, because caching is immensely useful and prevents repeated downloads. You just want to prevent downloads when you build a new release.

This solution worked for me.
let randomNum = Math.round(Math.random() * 10000);
src = "js/listener.js?" + randomNum;
Every time a random number will be generated and it'll be treated as a new request and won't be cached.

Related

How to check if browser cached JS library or not?

I have custom build JS library (which is swiper.js). Can I check if the browser has its CDN version in the cache before downloading it? Normally it's 130KB but my desired version (contain few fewer functions) is just 70KB so I don't want to add those extra KBs to get it from CDN if the user has not already cached it. Is this possible?
Just for clarity, you decide via your markup(html) as to what file the browser should download. So in the case of checking if there's a previous version of a file that you want to refresh, you can simply add a parameter at the end of the file to make the URL unique such that the browser doesn't use one that's prevously downloaded.
Here's an example link:
swipser.js?version=<version or date saved>
So each time a browser see this, it will not download unless the parameter has changed, or perhaps the user has cleared their cache

Reload from server for all files

I know it's possible to force reload from server using location.reload(true). However, let's say I used that to refresh index.html. If index.html loads a bunch of javascript files, those are still coming from the cache for me. Is there any way to ignore the cache for the duration of a request?
My use case is that I'm doing AB testing on my app, and want to provide a way for users to go back to the old version if something isn't working. But some of the URLs are the same, even though the files between versions are different. It would be nice to be able to handle this in JS rather than having to change every URL on the new version.
There is actually at least 535 different ways to reload a page via javascript, FYI ;).
Have you tried to put document on front? document.location.reload(true);
Try also this other option:
window.location.href = window.location.href;
or
history.go(0);
Sure, both are soft reload, but seems to work in certain situation.
If nothing works, you have to append random data to the url (like timestamp) to force the download from server, bypassing the cache.
If you want to bypass browser taking js files from cache, you need to fetch from server not just files like script.js but rather script.12345.js When you update your file on server, you change file's hash number to let's say script.54321.js And browser understands that the file is different, it must download it again. You can actually use Webpack for this purpose to automate things. In output instead of {filename: bundle.js} you write {filename: bundle.[hash].js}

Forcing browser to download a file rather than caching

I have a javascript file which internally calls a function to load an xml file.
$(document).ready(function()
{
urlVal ="web/help.xml";
}
The javaxcript is versioned so that the browser always loads it instead of
caching it
"./js/help_min.js?ver=${verNumber}"
I am facing an issue where browser downloads the latest js file but has cached help.xml included in js file.
is there a way that the browser will always load latest "hepl.xml" rather than caching it.
The proper apporach would be to fix the backend to send headers telling the browser not to cache the data (see i.e. How to control web page caching, across all browsers?). But if you cannot do that, make the request unique each time, i.e.
"./js/help_min.js?ver=${verNumber}&random=${something_random}"
where something_random value of random can be i.e. current time stamp (with millis). That way your request will not match the cache entry enforcing fetch on each request.
PS: you seem to also have design flaw, as by logic using the same ${verNumber} should return the same data, hence caching would be more than welcome to reduce the traffic and speed up loading time.

Caching preloaded images possible over page switch?

I'm currently trying to preload images for a webpage I'm creating as those images are quite big.
Currently I know (thanks to another post here) how to handle the images themselves via preloading them (via javascript pre loading and then displaying them in a canvas).
BUT whenever I switch the page the preloaded images need to be preloaded again, thus they are not cached.
So my question is: Is there any possibility to cache these images?
(or is it even best to put them into a session variable?)
The images themselves are quite big and can take up 1.5MB each (in total there are 20 images alone in the part that is currently already in existence, which takes about 4 seconds to preload).
As infos if necessary:
I'm using an apache server and php as primary language with javascript as support.
Edit:
As I forgot to mention it: The webserver I will finally store the site on is an external one (hosting provider) so I won't be able to edit the webserversettings themselves there
If the images don't change, try something like this in .htaccess:
#Set caching on image files for 11 months
<filesMatch "\.(ico|gif|jpg|png)$">
ExpiresActive On
ExpiresDefault "access plus 11 month"
Header append Cache-Control "public"
</filesMatch>
If you think this is not the right approach, like the images may change, just eager-load the images right when the page hits (warning, definitely a hack):
(function(){
var hiddenCache = document.createElement("div");
hiddenCache.style.display = "none";
document.body.appendChild(hiddenCache);
// or for loop if ECMA 3
myEagerLoadedImageUrls.forEach(function(urlStr){
var hiddenImg = document.createElement("img");
hiddenImg.src = urlStr;
hiddenCache.appendChild(hiddenImg)
});
})()
The browser already caches the images in its memory and/or disk cache as long as the headers coming from the server aren't telling it to avoid caching. The browser cache endures across page loads. SO, if your images have been loaded once on the first page, they should be in the browser cache already for the second page and thus when requested on the second page, they should load locally and not have to be fetched over the internet.
If you're looking for client-side code that can be used to preload images, there are many examples:
How do you cache an image in Javascript
Image preloader javascript that supports events
Is there a way to load images to user's cache asynchronously?
FYI, it is possible in newer browsers to use a combination of Local Storage and data URIs to implement your own image caching, but I'd be surprised if there was any real world situation where that was required and if you have a lot of images, you may run into storage limits on Local Storage quicker than limits on the size of the browser cache.

Forcing cache expiration from a JavaScript file

I have an old version of a JS file cached on users' browsers, with expiration set to 10 years (since then, I have learned how to set expires headers correctly on my web server). I have made updates to the JS file, and I want my users to benefit from them.
Is there any way my web server can force users' browsers to clear the cache for this one file, short of serving a differently named JS file?
In the future, if expires headers are not set correctly (paranoia), can my JS file automatically expire itself and force a reload after, say, a day has passed since it was cached?
EDIT: Ideally I want to solve this problem without changing HTML markup on the page that hosts the script.
In short... no.
You can add something to the end of the source address of the script tag. Browsers will treat this as a different file to the one they have currently cached.
<script src="/js/something.js?version=2"></script>
Not sure about your other options.
In HTML5 you can use Application Cache, that way you can control when the cache should expire
You need to add the path to the manifest
<!DOCTYPE HTML><html manifest="demo.appcache">
In your demo.appcache file you can just place each file that you want to cache
CACHE MANIFEST
# 2013-01-01 v1.0.0
/myjsfile.js
When you want the browser to download a new file you can update the manifest
CACHE MANIFEST
# 2013-02-01 v1.0.1
/myjsfile.js
Just be sure to modify the cache manifest with the publish date or the version (or something else) that way when the browser sees that the manifest has change it will download all files in it.
If the manifest is not change, the browser will not update the local file, even if that file was modify on the server.
For further information please take a look at HTML5 Application Cache
You could add a dummy parameter to your URLs
<script src='oldscriptname.js?foo=bar'></script>
[e: f; b]
The main problem is that if you set up the expiration with a simple "Expires" header, then the browsers that have the file cached won't even bother to contact you for it. Even if there were a way for the script to whack the browser in the head and clear the cache, your old script doesn't do that, so you have no way to get that functionality out to the clients.
You can force to reload an cacheated document with on javascript:
window.location.reload(true);
The true command indicate the browser must to reload the page without cache.

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