Find base name in URL in Javascript

I wouldn't actually use a regex in this case, but simply lastIndexOf and substring. Something like

function findBaseName(url) {
    var fileName = url.substring(url.lastIndexOf('/') + 1);
    var dot = fileName.lastIndexOf('.');
    return dot == -1 ? fileName : fileName.substring(0, dot);
}

Try this regular expression:

/([^/]+(?=\.[^/.]*$)|[^/.]+$)/

In your examples, assuming that the input string is the entire URL and nothing more, I've had success with

/\/[^\/]+(?=\.[^.]+$)|\/[^\/]+$/

This first tries to match everything from the last / until the last .; if there is no dot, it will then try to match everything from the last / until the end of the string.

The leading / is contained in the match (JavaScript doesn't support lookbehind, else I could have used that), so you'll need to chop off the first character of the match.

When you have access to a DOM, you can use the native HTMLHyperlinkElementUtils properties of an <a> tag:

function urlInfo (url) {

  var props = 'hash host hostname href origin password pathname port protocol username search';

  if (!window.urlInfoAnchorElement)
    window.urlInfoAnchorElement = document.createElement('a');

  urlInfoAnchorElement.href = url;

  return props.split(' ').reduce(function (m, v, i) {
    m[v] = urlInfoAnchorElement[v]; return m;
  }, {});

}

// Example:
urlInfo('http://localhost:4000/guidelines/7yQxvndK?get=sup&love=1#oiwjef');

/* => {
  hash: "#oiwjef"
  host: "localhost:4000"
  hostname: "localhost"
  href: "http://localhost:4000/guidelines/7yQxvndK?get=sup&love=1#oiwjef"
  origin: "http://localhost:4000"
  password: ""
  pathname: "/guidelines/7yQxvndK"
  port: "4000"
  protocol: "http:"
  search: "?get=sup&love=1"
} */

I recommend using the FileSystemObject activex. Sure, you need to mark it as safe in the registry to execute it without nag screens, but it' very useful. Your call... GetBaseName function does what you want.