Why are there numbers after the question mark in some JS/CSS URLs?

Question

Why do use like this filename.css?2 or filename.js?4 What are those numbers after question mark?

I did research online but I didn't find any answer.

Thanks!

It is revision numbers or cache busters as listed below. When people release a new version of their javascript, they increment this by one to force people to grab the latest version of their JS. — Kyle Muir, Sep 08 '14 at 22:58
You say you did research online, yet when I copy/paste the first line of your question into Google, we get the answer: http://stackoverflow.com/questions/4044085/what-does-used-after-javascript-filename-means Odd. — cookie monster, Sep 08 '14 at 23:08

rmobis · Answer 1 · 2014-09-08T23:16:42.190

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These are called cache busters.

Usually, when a browser downloads a file (CSS, JS, etc.) it caches it so that it doesn't have to download it later.

However, this is a problem when you decide to update your file, because the browser thinks it already has the latest version. To work around it, we use the cache busters. When you make a change to the file, you also change the number after the question marks, which tricks the browser into thinking this is a different file for which it doesn't have a cache it, and forces a re-download.

edited Sep 08 '14 at 23:16

answered Sep 08 '14 at 22:57

rmobis

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I opposed why did this answer got upvotes???? Wrong information!!!! – Bhojendra Rauniyar Sep 08 '14 at 23:07
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@C-link Nepal, mind telling what is wrong? – rmobis Sep 08 '14 at 23:09
Please read double times your answer and duplicate answers marked in the question... – Bhojendra Rauniyar Sep 08 '14 at 23:10
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They say pretty much what I said. So, again, do you mind pointing **exactly** what is wrong? – rmobis Sep 08 '14 at 23:11
The point you're giving is wrong like `it caches it so that it doesn't have to download it later.` but we use it for latest file download.... – Bhojendra Rauniyar Sep 08 '14 at 23:12
That's what caching is for, I believe? – rmobis Sep 08 '14 at 23:12
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/60853/discussion-between-raphael-and-c-link-nepal). – rmobis Sep 08 '14 at 23:13
We use query selector to remove cache but not to apply cache...! – Bhojendra Rauniyar Sep 08 '14 at 23:14
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If you read carefully, that's exactly what I said. – rmobis Sep 08 '14 at 23:14
Still, you've wrong point. remove `it caches it so that it doesn't have to download it later.` and then it will be fine... – Bhojendra Rauniyar Sep 08 '14 at 23:21
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But that's what it does. I'm not saying it is because of the cache buster, I'm simply saying the browser does it. I'd recommend you read it more carefully. – rmobis Sep 08 '14 at 23:27
NO, it doesn't, you may try yourself by using query selector and then changing your css file again and do clean refresh, it will show you latest or cached file???? The answer latest..... – Bhojendra Rauniyar Sep 08 '14 at 23:32
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OK, you clearly can't interpret what I'm saying. Never mind then. – rmobis Sep 08 '14 at 23:41
Am I missunderstanding your answer, Sorry then. I'll remove my -1 (As nice guy of you [having peace talks]). (but still you should try to understand that cache the file or clear the cache...) – Bhojendra Rauniyar Sep 08 '14 at 23:52

score 0 · Answer 2 · answered Sep 08 '14 at 22:58

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Sometimes JS scripts are created on the fly using server side technologies other times it is simply a version number to help with browser caching issues

answered Sep 08 '14 at 22:58

Devarsh Desai

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Why are there numbers after the question mark in some JS/CSS URLs?

2 Answers2