• Version:v12.13.0
• Platform:Linux myuser 4.15.0-74-generic Proposal: Introduce CI builds to GitHub PR process #84-Ubuntu SMP Thu Dec 19 08:06:28 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
• Subsystem:
  readline.createInterface
  asyncIterator

What steps will reproduce the bug?

if you perform something like
https://github.com/nodejs/node/blob/2a7432dadec08bbe7063d84f1aa4a6396807305c/test/parallel/test-readline-async-iterators.js

async function testSimple() {
  for (const fileContent of testContents) {
    fs.writeFileSync(filename, fileContent);

    const readable = fs.createReadStream(filename);
    const rli = readline.createInterface({
      input: readable,
      crlfDelay: Infinity
    });

    const iteratedLines = [];
    for await (const k of rli) {
      iteratedLines.push(k);
    }

    const expectedLines = fileContent.split('\n');
    if (expectedLines[expectedLines.length - 1] === '') {
      expectedLines.pop();
    }
    assert.deepStrictEqual(iteratedLines, expectedLines);
    assert.strictEqual(iteratedLines.join(''), fileContent.replace(/\n/gm, ''));
  }
}

If you add some kind of await xxx() between creating the interface and iterating, the iterator will miss lines. In my case I input 100k lines from a file, then output those same lines to a new file. several thousand lines will go missing.

How often does it reproduce? Is there a required condition?

100%
Need to add some await async between creating the interface and using for await

What is the expected behavior?

not to miss iterations

What do you see instead?

Additional information