Question

When you open a web page in your browser, the browser retrieves the page’s HTML text and parses it, much like the way our parser from Chapter 11 parsed programs. The browser builds up a model of the document’s structure and then uses this model to draw the page on the screen.

This representation of the document is one of the toys that a JavaScript program has available in its sandbox. You can read from the model and also change it. It acts as a live data structure: when it is modified, the page on the screen is updated to reflect the changes.

This is a book about getting computers to do what you want them to do. Computers are about as common as screwdrivers today, but they contain a lot more hidden complexity and thus are harder to operate and understand. To many, they remain alien, slightly threatening things.