The readlinePromises.createInterface() method creates a new readlinePromises.Interface instance.

const readlinePromises = require('node:readline/promises');
const rl = readlinePromises.createInterface({
  input: process.stdin,
  output: process.stdout
});

Once the readlinePromises.Interface instance is created, the most common case is to listen for the 'line' event:

rl.on('line', (line) => {
  console.log(`Received: ${line}`);
});

If terminal is true for this instance then the output stream will get the best compatibility if it defines an output.columns property, and emits a 'resize' event on the output, if or when the columns ever change (process.stdout does this automatically when it is a TTY).

Use of the completer function

The completer function takes the current line entered by the user as an argument, and returns an Array with 2 entries:

• An Array with matching entries for the completion.
• The substring that was used for the matching.

For instance: [[substr1, substr2, ...], originalsubstring].

function completer(line) {
  const completions = '.help .error .exit .quit .q'.split(' ');
  const hits = completions.filter((c) => c.startsWith(line));
  // Show all completions if none found
  return [hits.length ? hits : completions, line];
}

The completer function can also returns a Promise, or be asynchronous:

async function completer(linePartial) {
  await someAsyncWork();
  return [['123'], linePartial];
}