Promises API

class readlinePromises.Interface extends readline.InterfaceConstructor

Instances of the readlinePromises.Interface class are constructed using the readlinePromises.createInterface() method. Every instance is associated with a single input Readable stream and a single output Writable stream. The output stream is used to print prompts for user input that arrives on, and is read from, the input stream.

rl.question(query, options?): Promise

The rl.question() method displays the query by writing it to the output, waits for user input to be provided on input, then invokes the callback function passing the provided input as the first argument.

When called, rl.question() will resume the input stream if it has been paused.

If the readlinePromises.Interface was created with output set to null or undefined the query is not written.

If the question is called after rl.close(), it returns a rejected promise.

Example usage:

const answer = await rl.question('What is your favorite food? ');
console.log(`Oh, so your favorite food is ${answer}`);

Using an AbortSignal to cancel a question.

const signal = AbortSignal.timeout(10_000);

signal.addEventListener('abort', () => {
  console.log('The food question timed out');
}, { once: true });

const answer = await rl.question('What is your favorite food? ', { signal });
console.log(`Oh, so your favorite food is ${answer}`);

new readlinePromises.Readline(stream, options?): readlinePromises.Readline

rl.clearLine(dir): void

The rl.clearLine() method adds to the internal list of pending action an action that clears current line of the associated stream in a specified direction identified by dir. Call rl.commit() to see the effect of this method, unless autoCommit: true was passed to the constructor.

rl.clearScreenDown(): void

The rl.clearScreenDown() method adds to the internal list of pending action an action that clears the associated stream from the current position of the cursor down. Call rl.commit() to see the effect of this method, unless autoCommit: true was passed to the constructor.

rl.commit(): Promise

The rl.commit() method sends all the pending actions to the associated stream and clears the internal list of pending actions.

rl.cursorTo(x, y?): void

The rl.cursorTo() method adds to the internal list of pending action an action that moves cursor to the specified position in the associated stream. Call rl.commit() to see the effect of this method, unless autoCommit: true was passed to the constructor.

rl.moveCursor(dx, dy): void

The rl.moveCursor() method adds to the internal list of pending action an action that moves the cursor relative to its current position in the associated stream. Call rl.commit() to see the effect of this method, unless autoCommit: true was passed to the constructor.

rl.rollback(): void

The rl.rollback methods clears the internal list of pending actions without sending it to the associated stream.

readlinePromises.createInterface(options): readlinePromises.Interface

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

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

const { createInterface } = require('node:readline/promises');
const rl = 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).

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 return a Promise, or be asynchronous:

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