Nodejs REPL

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

Node.js provides an interactive shell called REPL ÔÇö Read-Eval-Print Loop. It lets you execute JavaScript line by line and see results instantly ÔÇö perfect for testing, debugging, and learning.

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How REPL Works

• Read: Reads user input and parses it into a JavaScript expression.
• Eval: Evaluates the expression.
• Print: Outputs the result.
• Loop: Repeats until exit (Ctrl+C twice).

Start the REPL

node
# > (you can now type JavaScript)

Simple Expressions

> 10 + 20 - 5
25
> "Hello " + "World"
'Hello World'

Working with Variables

> let name = "UpdateGadh"
undefined
> console.log(name)
UpdateGadh

Multi-line Expressions

> var x = 0
undefined
> do {
... x++;
... console.log("x:", x);
... } while (x < 3);

The Underscore Variable (_)

The _ variable holds the last evaluated expression:

> 5 + 10
15
> _ * 2
30

Useful REPL Commands

• .help ÔÇö list all REPL commands.
• .break ÔÇö exit a multi-line expression.
• .clear ÔÇö clear the current state.
• .save filename ÔÇö save session to a file.
• .load filename ÔÇö load JS into the session.
• Ctrl+C twice or Ctrl+D ÔÇö exit REPL.
• Tab ÔÇö autocomplete.

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Conclusion

The Node.js REPL is a simple but powerful tool for experimenting, testing snippets, and debugging. Mastering its commands speeds up your workflow. For more tutorials, stay tuned to .

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