Node.js REPL (Read-Eval-Print Loop) Terminal

Overview

The Node.js REPL is an interactive environment that allows developers to execute JavaScript code in real-time. It's a useful tool for testing snippets of code and understanding JavaScript behavior.

Key Concepts

What is REPL?

• Read: It reads the input from the user.
• Eval: It evaluates the input as JavaScript code.
• Print: It prints the result to the console.
• Loop: It continues this process until the user decides to exit.

Starting the REPL

To start the REPL, simply open your terminal and type node:

node

You will see a prompt (>) indicating that the REPL is ready to accept input.

Basic Commands

You can type any JavaScript expression and see the output immediately:

> 2 + 2
4

You can also declare variables:

> let x = 10;
> x * 2
20

Exiting the REPL

To exit the REPL, you can type .exit or press Ctrl + C twice.

Features of REPL

Multi-line Input

You can write multi-line statements by pressing Enter without a closing bracket:

> function add(a, b) {
...   return a + b;
... }

Built-in Functions

The REPL provides several built-in commands:

• .help: Shows help information.
• .editor: Enters multi-line input mode.
• .load <filename>: Loads JavaScript code from a file.
• .save <filename>: Saves the current session to a file.

Practical Example

Here's how you can use the REPL to test a simple function:

Call the function:

> greet("World")
"Hello, World!"

Define a function:

> function greet(name) {
...   return "Hello, " + name + "!";
... }

Start the REPL:

node

Conclusion

The Node.js REPL terminal is a powerful tool for JavaScript developers to experiment and learn. By using REPL, you can quickly test code snippets, understand JavaScript behavior, and streamline your development process.