Node.js is a popular open-source server environment built on Chrome's V8 JavaScript engine. One of the most useful tools provided by Node.js is the REPL (Read-Eval-Print-Loop), which allows you to execute JavaScript code interactively in a terminal.

The Node REPL is similar to a command-line interface for JavaScript. It is an interactive environment where you can enter JavaScript code and see the results immediately. It is great for testing out small pieces of code or experimenting with new features.

To start the Node REPL, simply open your terminal and type node. This will give you access to the Node REPL prompt where you can start typing your JavaScript code.

Here are some examples of how to use the Node REPL:

// Basic arithmetic
> 2 + 2
4

// String manipulation
> 'hello, world'.toUpperCase()
'HELLO, WORLD'

// Defining a variable
> var x = 10
undefined
> x
10

// Using a function
> function add(a, b) { return a + b }
undefined
> add(3, 5)
8

The Node REPL is a great tool for quickly testing out ideas, debugging code, or experimenting with new features. It can also be useful for prototyping code before integrating it into a larger project.

However, the Node REPL is not a substitute for a proper development environment. It is not designed for writing large or complex code, and it lacks many of the features and tools that are available in a full-fledged IDE or text editor.

Overall, the Node REPL is a useful tool for any JavaScript developer, but it should be used in tandem with a proper development environment to ensure the best results.