event driven vs promise driven

.nvmrc

v9.5.0

main.js

'use strict';

const readline = require('readline');

process.on('uncaughtException', err => {throw err});
process.on('unhandledRejection', err => {throw err});

async function* each_line(rl) {
  let lines = [];
  let unpark;
  rl.on('line', line => {
    lines.push(line);
    if (unpark) {
      unpark();
    }
  });
  let CLOSED = Symbol('CLOSED');
  rl.on('close', () => {
    lines.push(CLOSED);
    if (unpark) {
      unpark();
    }
  });
  while (true) {
    while (lines.length > 0) {
      let next = lines.shift();
      if (next === CLOSED) {
        return;
      } else {
        yield next;
      }
    }
    await new Promise(resolve => {
      unpark = resolve;
    });
  }
}

async function main() {
  const rl = readline.createInterface({
    input: process.stdin,
    output: null,
  });
  for await (let line of each_line(rl)) {
    console.log('line', line);
  }
  console.log('done');
}

main();

output.txt

~/junk/hello-async-generators$ printf '1\n2\n3\n' | node --harmony-async-iteration ./main.js 
line 1
line 2
line 3
done
~/junk/hello-async-generators$ node --harmony-async-iteration ./main.js 
1
line 1
2
line 2
3
line 3
done
~/junk/hello-async-generators$