What Does Appending "V=1" to CSS and JavaScript Urls in Link and Script Tags Do

What does appending ?v=1 to CSS and JavaScript URLs in link and script tags do?

These are usually to make sure that the browser gets a new version when the site gets updated with a new version, e.g. as part of our build process we'd have something like this:

/Resources/Combined.css?v=x.x.x.buildnumber

Since this changes with every new code push, the client's forced to grab a new version, just because of the querystring. Look at this page (at the time of this answer) for example:

<link ... href="http://sstatic.net/stackoverflow/all.css?v=c298c7f8233d">

I think instead of a revision number the SO team went with a file hash, which is an even better approach, even with a new release, the browsers only forced to grab a new version when the file actually changes.

Both of these approaches allow you to set the cache header to something ridiculously long, say 20 years...yet when it changes, you don't have to worry about that cache header, the browser sees a different querystring and treats it as a different, new file.

How does appending ?v=1 in script load new javascript

1. Most web servers will serve up a static file no matter what query string you put at the end of the URL.
2. Browsers cache data based on its URL.
3. Changing the URL to a different one means you won't get the cached version from the old URL but, given (1), the (new version of the) file stored in the same location on the server's disk will be served.

But how does this help? How the query string going to work? I don't have the file name changed nor did I wrote any script for doing anything with query string (?v=1) .

Then it doesn't help. You have to change the query string when you change the file.

What am I missing? Do I need to change the file name

No

or do I need to have a repository for sure to get this working?

You need to change the query string when you release a new version of the file.

One way to do that would be to use a build script that sets the URL to (for example) the commit id that last changed the file in a version control repository.

whats does the ?history=1 mean after a .js file?

It ensures that users have the latest version of a JS or CSS file in case an older version is cached by their browser.

What does ?v=2 mean in css?

If you set caches to expire far in the future adding ?v=2 will let the server know this is a new file but you won't need to give it a unique name ( saving you a global search and replace)

Append Dynamic version(variable ) in Script tag and stylesheet based on time

If you are looking for the shortest solution, how about this?

<script>document.write('<link href="/assets/cder.css?v=' + Date.now() + '" rel="stylesheet" />');</script>

A worthy alternative should be:

<script>
    var link = document.createElement('link');
    link.rel = 'stylesheet';
    link.href = '/assets/cder.css?v=' + Date.now();
    document.body.appendChild(link);
</script>

Well, you must escape the closing script tag as follows:

<script>document.write('<script src="/assets/abc.js?v=' + Date.now() + '"><\/script>');</script>

An example of how to add several scripts:

<script>  var scripts = [    '/assets/abc.js',    '/assets/def.js',  ];
  for (var i = 0; i < scripts.length; i++) {    var script = document.createElement('script');    script.onerror = function() {      alert('Could not load ' + this.src);    };     script.src = scripts[i] + '?v=' + Date.now();    document.body.appendChild(script);  }</script>