code: function isProxyForURL(noProxy, address) {
      // wildcard
      if (noProxy === '*') {
          return (null);
      }
  
      // otherwise, parse the noProxy value to see if it applies to the URL
      if (noProxy !== null) {
          var noProxyItem, hostname, port, noProxyItemParts,
              noProxyHost, noProxyPort, noProxyList;
  
          // canonicalize the hostname
          /* JSSTYLED */
          hostname = address.hostname.replace(/^\.*/, '.').toLowerCase();
          noProxyList = noProxy.split(',');
  
          for (var i = 0, len = noProxyList.length; i < len; i++) {
              noProxyItem = noProxyList[i].trim().toLowerCase();
  
              // no_proxy can be granular at the port level
              if (noProxyItem.indexOf(':') > -1) {
                  noProxyItemParts = noProxyItem.split(':', 2);
                  /* JSSTYLED */
                  noProxyHost = noProxyItemParts[0].replace(/^\.*/, '.');
                  noProxyPort = noProxyItemParts[1];
                  port = address.port ||
                      (address.protocol === 'https:' ? '443' : '80');
  
                  // match - ports are same and host ends with no_proxy entry.
                  if (port === noProxyPort &&
                      hostname.indexOf(noProxyHost) ===
                      hostname.length - noProxyHost.length) {
                      return (null);
                  }
              } else {
                  /* JSSTYLED */
                  noProxyItem = noProxyItem.replace(/^\.*/, '.');
                  var isMatchedAt = hostname.indexOf(noProxyItem);
  
                  if (isMatchedAt > -1 &&
                      isMatchedAt === hostname.length - noProxyItem.length) {
                      return (null);
                  }
              }
          }
      }
      return (true);
  }
docs: Check if url is excluded by the no_proxy environment variable