stream.transform 不能写入

Question

let transform = new stream.Transform({
        transform(chunk, encoding, cb) {
          this.push(chunk.toString())
        }
      });
      fs
        .createReadStream('./src/index.html')
        .pipe(transform);
      // transform.write('wefwef')
      console.log(transform.read().toString())

transform.read() 返回的是null是为什么