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JavaScript Book

Understanding the ECMAScript Specification

ECMAScript (often abbreviated ES) is the standard on which JavaScript is based. The specification is maintained by ECMA International (technical committee TC39).

Why a specification?

  • Ensures different implementations (browsers, Node.js) behave the same way.
  • Defines syntax, types, objects, and algorithms.
  • Allows developers to write code that works across environments.

ECMAScript versions are identified by their edition number (ES5, ES6/ES2015, ES2016, …). Since 2015, new features are released yearly.

How to check what’s supported?
Websites like caniuse.com and Node.green show compatibility tables.

Example: The let keyword was introduced in ES6. You can use it today in all modern environments.

let message = "Hello, ES6!";
console.log(message);

Understanding the specification helps you know what features are available and when you can safely use them without transpilers like Babel.