# C# vs JavaScript: an overview

JavaScript was made for browsers in 1995 and is standardized as ECMAScript. It looks like C#, with braces, if and for, but it's a different language. It runs in every browser, and in Node.js outside one.

Novice · JavaScript · Updated November 3, 2026

## After this lesson you can

- Explain where JavaScript runs, and the main ways it differs from C#

## Key takeaways

- JavaScript runs in a JavaScript engine: there's one in every web browser, and Node.js runs it outside the browser.
- JavaScript is standardized as ECMAScript, with a new version every year. ECMAScript 2015 (ES6) brought `let`, `const`, arrow functions and classes.
- C# is compiled, so many errors show before it runs. JavaScript runs straight away, so many errors show only when that line runs.
- C# types are static and never change; JavaScript types are dynamic, so a variable can hold any type and change it.
- Try JavaScript in the browser's Console (F12) or with `node app.js`; `console.log(...)` prints, like `Console.WriteLine(...)`.

JavaScript will feel familiar. It has braces, semicolons, `if`, `for`, `while`, `return`, and the same operators as C#. But it's a different language, with different rules underneath, and the differences are what this chapter is about.

## A short history

In 1995, Brendan Eich at Netscape wrote a small language in ten days to let web pages do more than sit still. Java was the exciting new language of the time, so the new one was named **JavaScript** to borrow some of its fame. The two are no more related than *car* and *carpet*.

In 1997 JavaScript was standardized, under the official name **ECMAScript**. Versions are named after the year: **ECMAScript 2015** (also called **ES6**) was the big one, bringing `let`, `const`, arrow functions and classes. A new version comes out every year, and today's browsers support them all.

## Where JavaScript runs

C# runs on .NET. JavaScript runs inside a **JavaScript engine**, and there's one in every web browser. That's what makes it special: it's the only language every browser runs, so every interactive web page uses it.

It also runs outside the browser, in **Node.js**, which takes the engine from Chrome and adds what a program needs to read files and talk to the network. You installed Node.js when you set up your computer.

You can run the examples in this chapter two ways:

- **In the browser:** press **F12**, open the **Console** tab, type JavaScript and press **Enter**.
- **With Node.js:** save the code as `app.js` and run `node app.js` in a terminal.

Either way, `console.log(...)` prints, like `Console.WriteLine(...)`:

```javascript
console.log('Hello from JavaScript');
console.log(2 + 3);
```

```text
Hello from JavaScript
5
```

## The big differences

| | C# | JavaScript |
|---|---|---|
| Runs on | .NET | A browser's JavaScript engine, or Node.js |
| Before it runs | Compiled: errors found before the program starts | Read and run straight away: many errors found only when that line runs |
| Types | **Static:** every variable has a type that never changes | **Dynamic:** a variable can hold any type, and change it |
| A program starts | At `Program.cs` | Wherever the browser or Node.js loads the file |
| Classes | Everything lives in classes | Functions and plain objects come first; classes are optional |

The next lessons take these one at a time, always starting from the C# you know.

## Check yourself

1 question to try on the lesson page.

## So what

JavaScript borrowed C#'s look (or rather, C and Java's), not its rules. Read it with fresh eyes, and you'll find a small, flexible language that runs everywhere, starting with every browser on earth.

## Key terms

- [ECMAScript](https://www.ask-codey.com/glossary/ecmascript)
- [JavaScript Engine](https://www.ask-codey.com/glossary/javascript-engine)
- [Node.js](https://www.ask-codey.com/glossary/node-js)
- [Browser Console](https://www.ask-codey.com/glossary/browser-console)
- [console.log()](https://www.ask-codey.com/glossary/console-log)

## Cheat sheets

- [C# vs JavaScript: an overview](https://www.ask-codey.com/cheat-sheets/csharp-vs-javascript-an-overview-cheat-sheet)

Source: https://www.ask-codey.com/lessons/csharp-vs-javascript-an-overview