Readline Module

Readline Module

The Readline module provides a way of reading a data stream one line at a time. It is most commonly used to build interactive Command Line Interface (CLI) tools, where you need to ask the user a question and wait for them to type an answer in the terminal.

1. Creating an Interface

To use the module, you must create a readline "interface" by linking a readable stream (the user's keyboard input) with a writable stream (the terminal output).

const readline = require('readline');

const rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout
});

2. Asking Questions

Once the interface is set up, you can use rl.question() to display a prompt and wait for user input.

const readline = require('readline');

const rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout
});
rl.question('What is your favorite programming language? ', (answer) => {
  console.log(Oh, ${answer} is a fantastic choice!);
  // You must close the interface, otherwise the script will hang forever!
  rl.close();
});

If you copy the code above into a file named prompt.js and run node prompt.js, the terminal will pause, wait for you to type your answer, hit enter, and then respond.