What is Node.js?

What you'll learn

What Node.js is, how it differs from browser JavaScript, and how to run a file with node.

Why it matters

Node lets you use one language, JavaScript, for both the front end and the back end. Servers, command-line tools and build tools for React and many other frameworks all run on Node.

Explanation

JavaScript was created to run inside web browsers. Node.js is a program that runs JavaScript on your own computer, outside a browser. It uses the same engine as Chrome (V8) but adds things a browser does not have: access to files, the network and your operating system.

Because there is no web page, there is no document or window. Instead you get Node features such as process, require / import, and modules like fs and http.

You run a script from a terminal:

node hello.js

Example

Save this as hello.js and run node hello.js:

const name = "Asha";
console.log("Hello from Node,", name);
console.log("Node version is a string:", typeof process.version);
console.log("2 + 3 =", 2 + 3);

Step-by-step walkthrough

1. node hello.js starts Node and tells it to run the file.
2. Node runs each line top to bottom, like in the browser.
3. console.log prints to your terminal instead of the browser console.
4. process.version is a Node-only value. We print its type, which is always string.

Try it yourself

Change the name, add another console.log, and run the file again. Press the button to see the expected output.

Common mistakes

• Using browser-only things like document or alert. They do not exist in Node.
• Running from the wrong folder, so node hello.js says "Cannot find module".
• Forgetting to save the file before running.
• Installing the wrong version. Use the LTS (long-term support) release.

Quick quiz

Summary

• Node.js runs JavaScript outside the browser.
• It has no document, but it has files, network and process.
• Run scripts with node file.js.

Next: splitting code into modules.