static classInit() {
    return new Promise((resolve, reject) => {
      if (StemmerJa.tokenizer) {
        resolve();
      } else {
        let dicPath = path.join(__dirname, '../node_modules/kuromoji/dict');
        if (!fs.existsSync(dicPath)) {
          dicPath = path.join(
            __dirname,
            '../../../../node_modules/kuromoji/dict'
          );
          if (!fs.existsSync(dicPath)) {
            dicPath = './node_modules/kuromoji/dict';
          }
        }
        kuromoji.builder({ dicPath }).build((err, tokenizer) => {
          if (err) {
            reject(err);
          } else {
            StemmerJa.tokenizer = tokenizer;
            resolve();
          }
        });
      }
    });
  }
Promise to initialize the class and get the tokenizer