Question

HTML can express various types of form fields, such as text fields, checkboxes, multiple-choice fields, and file pickers.

Such fields can be inspected and manipulated with JavaScript. They fire the "change" event when changed, the "input" event when text is typed, and various keyboard events. These events allow us to notice when the user is interacting with the fields. Properties like value (for text and select fields) or checked (for checkboxes and radio buttons) are used to read or set the field’s content.

When a form is submitted, its "submit" event fires. A JavaScript handler can call preventDefault on that event to prevent the submission from happening. Form field elements do not have to be wrapped in <form> tags.

When the user has selected a file from their local file system in a file picker field, the FileReader interface can be used to access the content of this file from a JavaScript program.

The localStorage and sessionStorage objects can be used to save information in a way that survives page reloads. The first saves the data forever (or until the user decides to clear it), and the second saves it until the browser is closed.

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.