code: function guessFunctionName(url, lineNo) {
          var reFunctionArgNames = /function ([^(]*)\(([^)]*)\)/,
              reGuessFunction = /['"]?([0-9A-Za-z$_]+)['"]?\s*[:=]\s*(function|eval|new Function)/,
              line = '',
              maxLines = 10,
              source = getSource(url),
              m;
  
          if (!source.length) {
              return UNKNOWN_FUNCTION;
          }
  
          // Walk backwards from the first line in the function until we find the line which
          // matches the pattern above, which is the function definition
          for (var i = 0; i < maxLines; ++i) {
              line = source[lineNo - i] + line;
  
              if (!_isUndefined(line)) {
                  if ((m = reGuessFunction.exec(line))) {
                      return m[1];
                  } else if ((m = reFunctionArgNames.exec(line))) {
                      return m[1];
                  }
              }
          }
  
          return UNKNOWN_FUNCTION;
      }
docs: Tries to use an externally loaded copy of source code to determine
  the name of a function by looking at the name of the variable it was
  assigned to, if any.
  @param {string} url URL of source code.
  @param {(string|number)} lineNo Line number in source code.
  @return {string} The function name, if discoverable.