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

Node.js provides a built-in REPL (Read-Eval-Print Loop) environment, allowing you to execute JavaScript code interactively. It is an essential tool for quick testing, debugging, and exploring Node.js features.

 

Key Features of REPL

1. Read

• Accepts user input.
• Example:

> 5 + 10

2. Eval

• Evaluates the entered JavaScript expression.
• Output:

15

3. Print

• Displays the result of the evaluated expression.

4. Loop

• Repeats the process for the next input.

 

Starting the REPL

1. Launch REPL

• Open your terminal and type:

node

• You will see the REPL prompt:

>

2. Execute Commands

• Type JavaScript commands directly.
• Example:

> console.log("Hello, Node.js REPL!");

Output:

Hello, Node.js REPL!
undefined

 

Useful Commands in REPL

1. Perform Calculations

• Example:

> 10 * 3

Output:

30

2. Define Variables

• Example:

> let x = 20;
> x + 5;

Output:

25

3. Multiline Input

• Use parentheses for multiline expressions:

> (function greet() {
... return "Hello from REPL!";
... })();

Output:

Hello from REPL!

4. Access Global Variables

• Example:

> __dirname

Output:

Current directory path

5. Exit REPL

• Use .exit or press Ctrl+C twice:

> .exit

 

REPL Shortcuts

 

Summary

Node.js REPL is a quick and interactive way to execute JavaScript code and test concepts. It’s especially useful for debugging and learning Node.js. Explore its features to enhance your coding experience!