replacer = function( key,value ) { // Exclude these keys from stringification
    const temp = _.some(['imp', 'warnings', 'computed', 'filt', 'ctrl', 'index',
      'safeStartDate', 'safeEndDate', 'safeDate', 'safeReleaseDate', 'result',
      'isModified', 'htmlPreview', 'display_progress_bar'],
       val  => key.trim() === val);
    if (temp) { return undefined; } else { return value; }
  }
Convert this object to a JSON string, sanitizing meta-properties along the
way. Don't override .toString().