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Hello, JavaScript!
JavaScript has a rich history.
It was created in 1995 as a simple language exclusively for web browsers, to “make web pages alive”. Since then it has greatly evolved.
Today we can use JavaScript on many platforms:
- In a web-browser, by embedding it into a web page.
- On a general purpose computer or a server, using Node.js and other means.
- ...Or actually on any device that has a special piece of software, called "JavaScript engine".
Technically, even a coffee machine can include its own JavaScript engine to allow programming of coffee recipes.
There's a formal language description called ECMAScript Language Specification, it describes how a JavaScript engine works. Sometimes we'll give references to it, but, though technically strict, it's hard to read for humans. At least at first.
Programs in JavaScript are called scripts.
Browsers have built-in JavaScript engines, so they can run scripts. They can be embedded right into HTML using the <script> tag and run automatically as the page loads.
For example, this HTML-page shows the "Hello, world!" message:
<!doctype html>
<script>
alert("Hello, world!");
</script>
To see it in action, you can click the "run" button in the upper-right corner. Also you can create a new file, e.g. my.html with this text and open it locally in a browser.
Depending on the environment, JavaScript may provide platform-specific functionality.
- In a browser, JavaScript can manipulate the web-page, send network requests, show messages and so on.
- In node.js we can use JavaScript to run a web-server, read and write arbitrary files.
- ...And so on.
In this course we concentrate on the core JavaScript, that's the same everywhere.
We'll try to keep browser-specific notes at minimum. After you learn the core, you can go in any direction: browsers, frameworks, servers and so on.
Turn the page to start learning JavaScript!