JS Versions

JS Versions

JavaScript is based on the ECMAScript specification. Over time, the language evolved through major editions such as ES3, ES5, ES6, and yearly releases after 2015.

Understanding versions helps you read older code and choose modern features safely.

JS 2015 (ES6)

ECMAScript 2015 (ES6) was the biggest update in JavaScript history. It introduced many modern features that define today's JavaScript style.

• let and const
• Arrow functions () => {}
• Classes
• Template literals
• Destructuring
• Default parameters
• Modules (import/export)
• Promises
• Map, Set, Symbol

// ES6 example
const greet = (name) => `Hello, ${name}`;
console.log(greet("Ozan"));

After ES6, ECMAScript switched to yearly releases (ES2016, ES2017, etc.).

JS 2009 (ES5)

ECMAScript 5 improved stability and introduced features that are still widely used today.

• Strict mode ("use strict")
• JSON support
• Array.prototype.forEach, map, filter, reduce
• Object.defineProperty

"use strict";

[1,2,3].forEach(function(n) {
  console.log(n);
});

Most modern browsers fully support ES5.

JS 1999 (ES3)

ECMAScript 3 was the standard that shaped early JavaScript. Many older websites were written using ES3 syntax.

• var variables
• Basic objects and arrays
• Basic regular expressions

var x = 10;
function sum(a, b) {
  return a + b;
}

Legacy code often still contains ES3-style patterns.

JS IE / Edge

Older versions of Internet Explorer had limited JavaScript support and many quirks.

IE11 does not support ES6 features like arrow functions, classes, or modules.

Modern Microsoft Edge (Chromium-based) supports modern ECMAScript features.

When supporting older browsers:

• Use transpilers (Babel)
• Use polyfills when needed
• Test on target environments

JS History

JavaScript was created in 1995 by Brendan Eich at Netscape.

ECMAScript became the standardized specification in 1997.

In 2015, ES6 marked a major evolution, and since then the language follows a yearly release cycle.

Modern JavaScript development focuses on:

• Readable and modular code
• Async programming
• Performance and security
• Compatibility awareness

Practical Advice

Use modern syntax (ES2015+) in new projects. Only consider older patterns when maintaining legacy systems.

Next Step

Continue with JS HTML DOM to learn how JavaScript interacts with web pages.