JavaScript

Turn a console message into a small, testable explanation.

Give a value a name and understand when it can change.

Make a decision without accidentally changing the value.

Turn a small task into a named operation.

Work with a collection without losing the original data.

Connect JavaScript to the document the browser actually created.

React to an action with a real, keyboard-accessible control.

Load data while handling both HTTP failures and invalid content.

Use browser storage for small preferences without making the page depend on it.