When you need to present dates in a way that is clear and meaningful to users, formatting is essential. Day.js makes this easy with its format() method, which converts a date object into a string using a pattern of format tokens. Each token represents a part of the date, such as the year, month, day, or day of the week. For instance, using 'YYYY-MM-DD' will output a date like 2023-03-14, while 'MMMM D, YYYY' will produce March 14, 2023. The token 'dddd' displays the full name of the day of the week, such as Tuesday. By combining different tokens, you can create custom date strings that fit your application's needs or match local conventions. Day.js supports a wide range of tokens, allowing you to display dates in formats like 'ddd, MMM D' for abbreviated weekday and month, or 'HH:mm:ss' for time. Adjusting the format string gives you full control over how dates appear to users, whether you need a compact numeric format or a more readable, friendly style.