Question

从fs.createWriteStream创建的文件读取数据时遇到问题。

在读取文件之后，而不是在调用文件时，看起来好像stream.write在程序的末尾执行了（这可以解释为什么在output_variable_3中什么都没有）。

使用的功能如下（简化）：

module.exports = async data1 => {
    console.log('start');
    try {
        const stream = fs.createWriteStream(filename_1, { flags: "a" });
        console.log('stream created');
        stream.write("some data", (err) => {
            if (err) {
                console.log(err.message);
            } else {
                console.log("data written");
            }
        });

        for (const variable_1 of object_1) {
            const variable_2 = await function2({
                // generates a buffer
            });
            stream.write(variable_2, (err) => {
                if (err) {
                    console.log(err.message);
                } else {
                    console.log("data written");
                }
            });
        }

        stream.end();
        console.log('stream ended');

        console.log('opening file');
        const variable_3 = fs.readFileSync(filename_1);
        console.log('file opened and read with data: ' + variable_3);
        return;
    } catch (error) {
        console.log(error);
    }
};

Output:
> start
> stream created
> stream ended
> opening file
> file opened and read with data: 
> data written
> data written

但是一旦代码运行，当我打开文件名_1（通过资源管理器）时，是否存在全部数据？！

Answer 1

让它排在最后。

没有意识到流函数不会返回承诺，所以我不得不手动返回承诺。

此处代码已更改：

module.exports = async data1 => {
    console.log('start');
    try {
        const stream = fs.createWriteStream(filename_1, { flags: "a" });
        console.log('stream created');
        stream.write("some data", (err) => {
            if (err) {
                console.log(err.message);
            } else {
                console.log("data written");
            }
        });

        for (const variable_1 of object_1) {
            const variable_2 = await function2({
                // generates a buffer
            });
            stream.write(variable_2, (err) => {
                if (err) {
                    console.log(err.message);
                } else {
                    console.log("data written");
                }
            });
        }

        stream.end();
        console.log('stream ended');

        console.log('opening file');
        const variable_3 = fs.readFileSync(filename_1);
        console.log('file opened and read with data: ' + variable_3);

        return new Promise(resolve => {
          stream.on('finish', () => {
              resolve('done');
              console.log("createNRRD is done");
          });
        });
    } catch (error) {
        console.log(error);
    }
};

无法使用“ fs.createWriteStream”

1 个答案: