Writable Stream empties the file but do not write expected content in nodeJS-CodePudding

This is my code to get an array of records and write them as CSV string one by one in a file. I cannot get the writable stream to write in the file. It just erases whatever is in the file and does not write the new data in.

const writeStream = fs.createWriteStream(process.env.SAVED_FILE);
const transformStream = new Stream.Transform({
    writableObjectMode: true,
    readableObjectMode: true,
})
transformStream._transform = (chunk, encoding, callback) => {
    console.log(chunk);
    transformStream.push("\""   chunk.join("\",\"")   "\"");
    callback();
}
const readable = new Stream.Readable({objectMode: true})
    .pipe(transformStream)
    .pipe(writeStream);
let records = [["a", "b"], [1, 2], ["c", "d"], [8, 9]];
records.forEach(record => readable.push(record));
readable.push(null);

writeStream.on("error", function (err) {
    console.log("there is an error!")
});
writeStream.on("end", function () {
    console.log("reached the end of the stream!")
});

Any help appreciated on this basic example !

CodePudding user response：

pipe() method returns the destination stream, i.e. the writable stream.

In your code,

const readable = new Stream.Readable({objectMode: true})
    .pipe(transformStream)
    .pipe(writeStream);

readable doesn't contains a reference to a readable stream like you expect. Instead, it refers to the last stream in the chain, i.e. writeStream and you cannot call push on a writable stream.

Change your code as shown below:

const readable = new stream.Readable({ objectMode: true });

readable
  .pipe(transformStream)
  .pipe(writeStream);