Node.js Readline Basics

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The readline module in Node.js provides an easy way to interact with the command line and get user input. It can be used to read data from a readable stream (like process.stdin) one line at a time. In this article, we will cover the basics of using the readline module to get user input in a Node.js application.

Importing the Readline Module

First, you need to import the readline module. You can do this using the require function:

const readline = require("readline");

Creating a Readline Interface

Next, you need to create an instance of the readline.Interface class. This class represents a readline interface and provides methods for reading and writing data to a readable and writable stream. You can create an instance of this class using the readline.createInterface() method:

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

Here, we pass an object with two properties: input and output. The input property should be a readable stream, and the output property should be a writable stream. In this case, we use process.stdin and process.stdout, which represent the standard input and output streams, respectively.

Reading User Input

To read a line of user input, you can use the rl.question() method. This method takes two arguments: a prompt to display to the user and a callback function to execute when the user enters their input. The callback function will receive the user input as its first argument:

rl.question("What is your name? ", (name) => {
    console.log(`Hello, ${name}!`);
    rl.close();
});

Here, we display the prompt "What is your name?" and wait for the user to enter their input. When they do, we print a greeting with their name and close the readline interface using the rl.close() method.

Closing the Readline Interface

It's important to close the readline interface when you're done using it. This releases the resources associated with the interface and allows the Node.js process to exit. You can close the interface using the rl.close() method, as shown in the previous example.

Full Example

Here's a complete example that demonstrates how to use the readline module to get user input in Node.js:

const readline = require("readline");

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

rl.question("What is your name? ", (name) => {
    console.log(`Hello, ${name}!`);
    rl.close();
});

Now you have a basic understanding of how to use the readline module in Node.js to get user input. You can use this knowledge to create more interactive command-line applications and gather information from users as needed.

FAQ

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

rl.question("What's your name? ", (answer) => {
    console.log(`Hello, ${answer}!`);
    rl.close();
});

rl.on("line", (input) => {
    console.log(`Received input: ${input}`);
});
rl.on("close", () => {
    console.log("Readline interface closed.");
});

const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout,
    prompt: "My Custom Prompt > "
});
rl.prompt();