code: function getRelativeFilename(basePath, filename) {
          if (!filename || filename.substr(0, basePath.length) !== basePath) {
              return;
          }
  
          return filename.substr(basePath.length);
      }
docs: Computes filename as relative to the basePath. For example:
  basePath: /foo/bar/, filename: /foo/bar/baz.txt
  returns: baz.txt
  
  The net effect is that the common prefix is stripped away. If basePath is not
  a prefix of filename, then undefined is returned.
  
  @param {string} basePath Path against which we're computing the relative path
  @param {string} filename Full path to the file for which we are computing a relative path
  @return {string} relative path