How do you start the Node.js REPL?
Quick answer: Install Node.js, then either run the node command from any terminal or launch the "Node.js" entry that the Windows installer adds to the Start Menu. Both open the REPL — Node.js's interactive Read-Eval-Print-Loop. The video above shows both methods on Windows.
What is the REPL in Node.js?
The REPL (Read-Eval-Print-Loop) is an interactive shell that executes JavaScript one line at a time and prints each result immediately. It ships with every Node.js installation; the official Node.js REPL API documentation describes it as a way to evaluate expressions interactively without writing files first.
What are the two ways to launch it on Windows?
- Start Menu: search for "Node.js" and open the result — this opens a terminal pre-loaded with the REPL.
- Command Prompt: type
nodeand press Enter. A>prompt appears when the REPL is ready.
To exit, press Ctrl+C twice or type .exit. The full list of REPL dot-commands lives in the official REPL documentation.
What can you do inside the REPL?
- Evaluate expressions: typing
2 + 2prints4. - Declare variables and reuse them across lines.
- Load built-in modules interactively, e.g.
const os = require('os'), then callos.platform(). - Inspect anything: typing a variable name prints its value, which makes the REPL a quick debugging tool.
Where does Node.js itself come from?
If node is not recognized, install the runtime first from the official Node.js download page, which offers LTS and Current releases for Windows, macOS, and Linux. After installing, reopen Command Prompt so the PATH updates, then run node -v to confirm.
Frequently Asked Questions
Is the REPL the same as the browser console?
Similar idea, different runtime. The browser console executes JavaScript against web page APIs; the Node.js REPL executes JavaScript against Node APIs like fs and os. Both print results immediately.
Do I need to create a file to use the REPL?
No. That is its main advantage — you test snippets directly. Files come later, when code is worth saving.
Does the REPL work on macOS and Linux too?
Yes. Open any terminal and run node; the REPL behaves identically across platforms per the official documentation.
Why does my REPL show "undefined" after some lines?
The REPL prints the completion value of each statement. Statements like assignments or console.log() calls complete with no value, so the REPL prints undefined — normal behavior, not an error.
Sources
How to Start REPL | Node Js | Tutorial For Beginner https://youtu.be/Et7wz0T_fnw #nodejs #node #node_video #REPL #js #tutorial How to Start REPL The first important point is that your system must install node.js There are 2 ways to Start REPL: - 1. Go to the Start Menu search Node.js And Open it. 2. Open CMD (Command Prompt) and write the Command node Hello World Program | Web application Node Js | Tutorial For Beginner https://youtu.be/gDQ-jU5bo7w Software Installation | Node Js :- https://youtu.be/7gi6lgK-BIA Node Js Download Link:- https://nodejs.org/en/download Software Installation Playlist https://www.youtube.com/playlist?list=PLHeKsaIQNmlqvVEHF9mMfUPMCPtIjlARL #Subscribe the #Channel #Link :- #bansodetechsoluiotn #ajupgrading https://www.youtube.com/c/AjUpgradingBANSODETECHSOLUTION?sub_confirmation=1 IF any #Query or #Doubt #DM on #Instagram :- #bansode_ajay_2102 https://www.instagram.com/bansode_ajay_2102?r=nametag Whatsapp Channel Link https://whatsapp.com/channel/0029VaOllPkEKyZAoy7K791X