MEPX
Chapter 1 of 16All chapters
  1. 1Introduction
  2. 2Syntax and statements
  3. 3Variables and scope
  4. 4Data types
  5. 5Comparison and coercion
  6. 6Strings
  7. 7Numbers and maths
  8. 8Arrays
  9. 9Objects
  10. 10Functions
  11. 11Conditions and loops
  12. 12Classes
  13. 13The DOM
  14. 14Events
  15. 15Promises and async
  16. 16Modules

Chapter 1 of 16

Introduction

Where JavaScript runs and what it is for.

One language, several homes

JavaScript began in the browser in 1995 and now also runs servers, build tools and desktop apps through Node. The language is standardised as ECMAScript, which is why you see names like ES2015.

  • The browser adds the DOM and fetch. Node adds files, processes and networking.
  • The core language is the same in both, so most of what you learn moves across.

Running it

In a browser, a script tag loads a file or the console runs a line at a time. With Node installed, node file.js runs the same code outside a page.