How to check if browser cached JS library or not?

Question

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?

Answer 1

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