JavaScript: variables, functions and the DOM

The language of the browser, and how it reaches into your page and edits it.

13 min read · Lesson 4 of 6 · Pro

Why JavaScript exists

HTML gives structure. CSS gives looks. Neither can react. Nothing can change after the page loads. JavaScript is the third piece: it runs inside the browser and can read and change the page while the user is on it.

Add it just before the closing </body> tag:

Code

  <script src="app.js"></script>
</body>

Why at the bottom? Because the script runs the moment the browser reaches it. If it runs before the elements exist, it finds nothing.

Variables

JavaScript

let count = 0;          // can be reassigned
const name = "Ravi";    // cannot be reassigned
count = count + 1;

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