Weird javascript behaviour on server

My javascript works fine on local machine, but breaks whenever I try to run it on a server. The script changes buttons colour on click.

javascript on server (After F12 inspection)



javascript file:


The file on my server is alright, same code as local javascript above.

HTML head:

  <meta http-equiv="content-type" content="text/html" charset="utf-8">
  <meta http-equiv="content-langauge" content="pl">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <link rel="stylesheet" content="text/css" href="style.css">
  <link rel="icon" type="image/png" href="images/favicon.png">
  <script src="javascript.js"></script>
  <title>KOYOT web design</title>

JSFiddle link (same thing happens as in server):

Server link: