[majewsky]

Examples where some JS has its place for forms:

1. The browser already gives you <input type="number"> or <input type="date">, but you may also need <input type="credit-card-number"> or <input type="expiration-date">. For credit card numbers (or bank account numbers) specifically, you want the input field to break it up into groups of 4 digits similar to how it's printed on the card, to make it easier for the user to double-check their input.

2. Suppose you're in the checkout workflow of a webshop. While choosing a shipping method and destination, I want to see the final price update to reflect my selection immediately. I don't want to flip back and forth between selecting a shipping method and seeing the actual cost on the final confirmation screen.