myrepl.mjs

import tty from 'tty'
import { emitKeypressEvents } from 'readline';

let drain;
process.stdout.on('drain', () => { drain() });
const waitForDrain = () => new Promise(r => {drain = r});
function waitForDrainify(func) {
  return async (...args) => {
    if (!func(...args)) {
      await waitForDrain();
    }
  }
};
const write = waitForDrainify((s) => process.stdout.write(s));
const moveCursor = waitForDrainify((x, y) => process.stdout.moveCursor(x, y));

(async function simpleRepl() {
  emitKeypressEvents(process.stdin);
  process.stdin.setRawMode(true)
  let currentInput = '';

  const processInp = async (str, key) => {
    await moveCursor(0, 1);
    const info = `pressed ${key.name}`
    await write(info)
    await moveCursor(-info.length, -1)

    if (key.name === 'return') {
      await write(`\n${currentInput.toUpperCase()}\n> `)
      currentInput = ''
    } else if (key.name === 'backspace') {
      if (currentInput.length) await write('\b \b')
      currentInput = currentInput.slice(0, currentInput.length-1);
    } else {
      currentInput += key.sequence
      await write(key.sequence);
    }
  };

  let lastKeyPromise = Promise.resolve();
  process.stdin.on('keypress', async (str, key) => {
    if(key.sequence === '\u0003') { // this is ctrl-c
        process.exit();
    }
    const prevKeyFinished = lastKeyPromise;
    let inputDoneBeingProcessed;
    lastKeyPromise = new Promise(r => {inputDoneBeingProcessed = r});
    await prevKeyFinished;
    await processInp(str, key)
    inputDoneBeingProcessed();
  });

  await write('> ')
})()