parcel-bundler/src/builtins/bundle-url.js

var bundleURL = null;
function getBundleURLCached() {
  if (!bundleURL) {
    bundleURL = getBundleURL();
  }

  return bundleURL;
}

function getBundleURL() {
  // Attempt to find the URL of the current script and use that as the base URL
  try {
    throw new Error;
  } catch (err) {
    var matches = ('' + err.stack).match(/(https?|file|ftp|chrome-extension|moz-extension):\/\/[^)\n]+/g);
    if (matches) {
      return getBaseURL(matches[0]);
    }
  }

  return '/';
}

function getBaseURL(url) {
  return ('' + url).replace(/^((?:https?|file|ftp|chrome-extension|moz-extension):\/\/.+)\/[^/]+$/, '$1') + '/';
}

exports.getBundleURL = getBundleURLCached;
exports.getBaseURL = getBaseURL;