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

📘 Node.js 👁 50 views 📅 Nov 05, 2025
⏱ Estimated reading time: 1 min

The Node.js REPL is an interactive environment that allows you to execute JavaScript code line by line and immediately see the output.

1. REPL Cycle

  1. Read – Reads the user input

  2. Eval – Evaluates the JavaScript code

  3. Print – Displays the result

  4. Loop – Waits for the next command

2. Starting the REPL

Open a terminal and type:

node

You will see:

>

3. Basic Usage

> 2 + 3
5

> let x = 10;
undefined

> x * 2
20

4. Special REPL Commands

CommandDescription
.helpList all REPL commands
.exitExit the REPL
.clearClear the context
.save file.jsSave session to a file
.load file.jsLoad a file into REPL

5. Multiline Code

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

6. Global Objects Access

You can directly access:

  • console

  • process

  • global

  • __dirname

  • __filename

7. Advantages

  • Fast testing and debugging

  • No file creation required

  • Ideal for learning and experimentation

8. Limitations

  • Not suitable for large applications

  • Session data is lost on exit

9. Use Cases

  • Testing small code snippets

  • Debugging logic

  • Exploring Node.js APIs

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