Your First JavaScript Program
What JavaScript is, where it runs, and how to print with console.log.
JavaScript is the programming language of the web. Every modern browser has a JavaScript engine built in, so you already have everything you need to start. Outside the browser, tools such as Node.js let you run JavaScript on servers and on your own computer.
On this site, every JavaScript example has a Run button. Press it and the code runs right here in your browser, safely in the background.
Hello, world
The simplest way to show something is console.log(). It prints its arguments to the console, a text panel used by developers.
console.log("Hello, world!");Hello, world!
Logging several values
console.log accepts any number of values and puts a space between them. Numbers are calculated before they are printed.
console.log("Minutes in a day:", 24 * 60);
console.log("Is 10 greater than 3?", 10 > 3);
// This is a comment. JavaScript ignores it.
console.log("Done");Minutes in a day: 1440 Is 10 greater than 3? true Done
Running JavaScript on your computer
To run a file outside the browser, install Node.js from nodejs.org, save your code as hello.js, and run:
node hello.jsTry editing the examples above: change the text, press Run, and see what happens. Breaking things on purpose is a great way to learn.