it can read data in data event even if I have added readable event before

[yunnysunny]

Affected URL(s)

https://nodejs.org/docs/latest/api/stream.html#two-reading-modes

Description of the problem

As the docs said:

Adding a 'readable' event handler automatically makes the stream stop flowing, and the data has to be consumed via readable.read(). If the 'readable' event handler is removed, then the stream will start flowing again if there is a 'data' event handler.

I added both the readable and data event listener, then I found both of them emit.

const { Readable } = require('stream');

class MyReadable extends Readable {
    _read () {
        console.log('_read has been called');
    }
}

const reader = new MyReadable();
const initSize = 6;
for (let i = 0; i < initSize; i++) {
    reader.push(Buffer.from([i & 0xff]));
}
reader.on('readable', function () {
    console.log('get data', reader.read());
});

reader.on('data', (chunk) => {
    console.log('stream mod2', reader.readableFlowing);
    console.log('data event', chunk);
});

console.log('stream mode', reader.readableFlowing);

The output of code is:

stream mode false
_read has been called
stream mode2 false
data event <Buffer 00 01 02 03 04 05>
get data <Buffer 00 01 02 03 04 05>

It seemed that the buffer can been read in flowing mode and paused mode at same time.

[jakecastelli]

IIRC this is by design, please see:

If both 'readable' and 'data' are used at the same time, 'readable' takes precedence in controlling the flow, i.e. 'data' will be emitted only when stream.read() is called. The readableFlowing property would become false. If there are 'data' listeners when 'readable' is removed, the stream will start flowing, i.e. 'data' events will be emitted without calling .resume().