How do I change a filename on-download with javascript?

Question

The script adds a download link for videos (on a specific site). How do I change the filename to something else while downloading?

Example URL:
"http://website.com/video.mp4"

Example of what I want the filename to be saved as during download:
"The_title_renamed_with_javascript.mp4"

Answer 1

This actually is possible with JavaScript, though browser support would be spotty. You can use XHR2 to download the file from the server to the browser as a Blob, create a URL to the Blob, create an anchor with its href property set to that URL, set the download property to whatever you want the filename to be, and then click the link. This works in Google Chrome, but I haven't verified support in other browsers.

window.URL = window.URL || window.webkitURL;

var xhr = new XMLHttpRequest(),
      a = document.createElement('a'), file;

xhr.open('GET', 'someFile', true);
xhr.responseType = 'blob';
xhr.onload = function () {
    file = new Blob([xhr.response], { type : 'application/octet-stream' });
    a.href = window.URL.createObjectURL(file);
    a.download = 'someName.gif';  // Set to whatever file name you want
    // Now just click the link you created
    // Note that you may have to append the a element to the body somewhere
    // for this to work in Firefox
    a.click();
};
xhr.send();