What JavaScript Is (and Why It Is Not Java)

Maria decides to learn JavaScript. She types "JavaScript course" into a search box. Half of what comes back teaches Java. One course opens with public static void main, and she wonders if she has already fallen behind.

She has not. She has met the oldest naming accident in programming. Java and JavaScript share four letters and very little else. As an old joke puts it, Java is to JavaScript what a car is to a carpet.

This lesson clears that up first, because every later lesson assumes you are reading about the right language. Then it gives JavaScript a date of birth, a standard and a version number you can point at.

JavaScript in one sentence

Here is the sentence to remember.

JavaScript is the programming language every web browser runs, standardised under the name ECMAScript, and now used on servers, phones and desktops too.

Three parts of that sentence matter. A programming language is a written set of rules for giving a computer instructions. A web browser is the program you use to open websites, such as Chrome, Firefox, Safari or Edge. Every one of them ships with JavaScript built in, so you do not install anything to use it.

The third part, "standardised", means a written rulebook exists. Anyone can build a program that reads JavaScript, as long as it follows that rulebook. That is why the same code runs in four different browsers made by four different companies.

So JavaScript is one language with one rulebook, and many programs that run it.

Java and JavaScript: two languages, one marketing decision

In 1995 a programmer named Brendan Eich built the first version of JavaScript at Netscape, the company behind the most popular browser of the day. He had about ten days. The language was called Mocha, then LiveScript.

That same year Sun Microsystems released Java, and Java was the most talked-about language in the industry. Netscape and Sun made a deal, and LiveScript was renamed JavaScript in December 1995. The name was marketing. The languages were already different, and they have grown further apart every year since.

If you only remember three lines of that table, take these. Java is compiled ahead of time into bytecode; JavaScript is sent as text and run by an engine. Java makes you write each variable's type; JavaScript does not. A Java program lives inside a class; a JavaScript program can be a single line.

Here is the same greeting in Java. Do not try to run it here. Just notice how much ceremony surrounds one line of work.

public class Hello {
    public static void main(String[] args) {
        String name = "Maria";
        System.out.println("Hello, " + name + "!");
    }
}

The JavaScript version is two lines, and you will see it in Example 2. So if a tutorial shows System.out.println or public static void, you are reading Java, not JavaScript.

A timeline from 1995 to today

JavaScript has changed a lot in thirty years. You do not need every date, but five of them explain most of what you will read online.

Between 1999 and 2009 the language barely moved. A big planned update, the fourth edition, was abandoned in 2008. ES5 in 2009 was a careful step instead. Then ES2015 arrived with so much at once that people still call everything after it "modern JavaScript".

Since 2016 a new edition has come out every year, each one small. So ES2022 and ES2023 differ by a handful of features. ES5 and ES2015 differ by a whole way of writing code.

ECMAScript, ES2015 and ES2023: what the names mean

The rulebook is not written by any one browser company. It is written by a committee called TC39, inside a standards body called Ecma International. The rulebook's official name is ECMA-262, and the language it describes is called ECMAScript.

Why the second name? The word "JavaScript" is a trademark, owned today by Oracle, which bought Sun. So the standard uses a name nobody owns. In practice, "JavaScript" is what people say and "ECMAScript" is what the rulebook says. They mean the same language.

Editions used to have numbers: ES3, ES5, ES6. Since 2015 they are named after their year. ES6 and ES2015 are two names for the same edition, and you will see both online.

ES2023

This track writes ES2023 JavaScript. That matters for one practical reason. An engine (the program that runs JavaScript) only understands the features of the editions it was built for. Node.js 22, which runs your code on the Playground, understands all of ES2023. So nothing in this track will ask the Playground for a feature it does not have.

When a later lesson uses something newer, such as Object.groupBy from ES2024, it says so and marks it "ES2024". So the edition name is a promise about what will run.

Your first look at JavaScript code

You will run code properly in lesson 05. For now, read these three programs and their output. Each one is complete. The line console.log(...) means "print this", and lesson 05 explains it fully.

console.log("Hello, Maria!");

Hello, Maria!

const name = "Maria";
console.log("Hello, " + name + "!");
console.log("Welcome to JavaScript.");

Hello, Maria!
Welcome to JavaScript.

const born = 1995;
const firstStandard = 1997;
const modern = 2015;
console.log("JavaScript was born in " + born + ".");
console.log("Its first standard came " + (firstStandard - born) + " years later.");
console.log("Modern JavaScript began in " + modern + ".");

JavaScript was born in 1995.
Its first standard came 2 years later.
Modern JavaScript began in 2015.

#include <stdio.h>

int main(void)
{
    const char *name = "Maria";
    printf("Hello, %s!\n", name);
    printf("Welcome to JavaScript.\n");
    return 0;
}

String name = "Maria";
console.log(name);

Next you will find out where JavaScript actually runs. It is four places, and one of them is in your pocket.