saveAs( filename, format ) {

    // If format isn't specified, default to FRESH
    const safeFormat = (format && format.trim()) || 'FRESH';

    // Validate against the FRESH version regex
    // freshVersionReg = require '../utils/fresh-version-regex'
    // if (not freshVersionReg().test( safeFormat ))
    //   throw badVer: safeFormat

    const parts = safeFormat.split('@');

    if (parts[0] === 'FRESH') {
      this.imp.file = filename || this.imp.file;
      FS.writeFileSync(this.imp.file, this.stringify(), 'utf8');

    } else if (parts[0] === 'JRS') {
      const useEdgeSchema = parts.length > 1 ? parts[1] === '1' : false;
      const newRep = CONVERTER.toJRS(this, {edge: useEdgeSchema});
      FS.writeFileSync(filename, JRSResume.stringify( newRep ), 'utf8');
    } else {
      throw {badVer: safeFormat};
    }
    return this;
  }
Save the sheet to disk in a specific format, either FRESH or JSON Resume.