What Is It?

When an HTML page is loaded, the browser parses it and generates the Document Object Model (DOM).

The DOM is a tree-structure of nodes where each node is an element (like a form, an image or a simple div container).

DOM can be manipulated with JavaScript using the standard DOM API.

When the HTML page is loaded, the browser executes the JavaScript indicated using the script tag.

<script>
    alert('test');
</script>

<script src="/assets/script.js"></script>