Getting Started with JavaScript

JavaScript · Reference cheat sheet

📋 Overview

JavaScript (JS) is the language of the web browser and a popular choice on servers via Node.js. You write .js (or .mjs) files, or run snippets in browser DevTools / Node’s REPL.

🔧 Core concepts

Idea	Meaning
ECMAScript (ES)	The language standard JS implements
Browser runtime	JS + DOM + Web APIs
Node.js	JS outside the browser (files, servers, CLIs)
Engine	V8, SpiderMonkey, etc. execute your code
Module	Reusable file using `import` / `export`

Ways to try JS: browser console (F12), Node (node), or a simple HTML file with a <script> tag.

💡 Examples

Check Node version:

node --version

REPL one-liner:

node

> console.log("Hello")
Hello
> 2 + 2
4

Script file (hello.js):

console.log("Hello from Node");

node hello.js

In the browser (inline):

<!DOCTYPE html>
<html>
  <body>
    <script>
      console.log("Hello from the browser");
    </script>
  </body>
</html>

⚠️ Pitfalls

Browser JS and Node share the language but not all APIs (document vs fs).
Old tutorials use var everywhere — prefer let / const.
Forgetting to open the console makes console.log look like “nothing happened.”
File protocol + modules can be awkward; use a tiny local server when learning modules.

Getting Started with JavaScript

Getting Started with JavaScript

📋 Overview

🔧 Core concepts

💡 Examples

⚠️ Pitfalls

🔗 Related

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