Change name of download in javascript

HTML5 provides the a[download] attribute which lets you rename a file. This example will download link.txt and rename it something.txt.

​<a download="something.txt" href="link.txt">asdf</a>​​​​​​​​​​​​​​​​​​​​​​​​​​​

Note that this only works on same-origin URLs (i.e. not across different domains).

You can use Filesaver.js script written by eligrey(Im using angularjs in the example here) You can achieve the same in classic javascript using XmlHttpRequest object

//In your html code , add these : ->
<script src="https://rawgit.com/eligrey/FileSaver.js/master/FileSaver.js" type="text/javascript"></script>
 <script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/angularjs/1.5.7/angular.min.js"></script>
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/angularjs/1.5.7/angular-animate.js"></script>
//In your Javascript:- 

$http({
        url: "url where the file is located",
        method: "GET",
        responseType: "blob"
    }).then(function (response) {

saveAs(response.data,"newfilename.extension");

})

No, you cannot change this from the client side (HTML or javascript). You need to change it from the server. One way is to use a server side script which will set the Content-Disposition HTTP response header:

Content-Disposition: attachment; filename=somecustomname.txt