window.location is an accessor property, and getting its value gives you an object, not a string, and so it doesn't have an indexOf function. (It's perfectly understandable that people sometimes think it's a string, since when you set its value, the accessor property's setter accepts a string; that is, window.location = some url; actually works. But when you get it, you don't get a string.)

You can use window.location.toString(), String(window.location), or window.location.href to get a string for it if you like, or use any of its various properties to check specifics. From the link, given example url http://www.example.com:80/search?q=devmo#test:

• hash: The part of the URL that follows the # symbol, including the # symbol. You can listen for the hashchange event to get notified of changes to the hash in supporting browsers.
  Example: #test


• host: The host name and port number.
  Example: www.example.com:80


• hostname: The host name (without the port number).
  Example: www.example.com


• href: The entire URL.
  Example: http://www.example.com:80/search?q=devmo#test


• pathname: The path (relative to the host).
  Example: /search


• port: The port number of the URL.
  Example: 80


• protocol: The protocol of the URL.
  Example: http:


• search: The part of the URL that follows the ? symbol, including the ? symbol.
  Example: ?q=devmo

For instance, for your quoted example, you might check window.location.hostname === localhost.