Node.js REPL & Executing Scripts

Using the REPL and Running Scripts

REPL stands for Read-Eval-Print-Loop. It provides an interactive command-line environment for testing JavaScript snippets and Node.js APIs in real time.

Starting the REPL

Launch the REPL by typing node in your terminal:

$ node
Welcome to Node.js v20.10.0.
Type ".help" for more information.
> 5 + 10
15
> const name = "Express";
undefined
> `Hello ${name}`
'Hello Express'
> .exit

Useful REPL Commands

• .help : List all dot commands.
• .break / .clear : Reset multiline input context.
• .exit : Exit the REPL session (or press Ctrl+C twice).
• _ (Underscore) : Stores the result of the last evaluated expression.

Running JavaScript Files

Execute scripts by passing the file path to the node command:

$ node server.js --env=production

// server.js
console.log("Command Line Args:", process.argv);
// process.argv[0]: Path to node executable
// process.argv[1]: Path to executed script
// process.argv[2...]: User arguments passed

TL;DR

• REPL = Read-Eval-Print-Loop for interactive JavaScript testing.
• Use node script.js to run JS files.
• process.argv contains array of command-line arguments.