You already know that Drupal's form API is great. And you may have heard of ways to make forms have dynamic behavior. But Drupal actually has several different options, and at least one is probably new to you. We'll cover:

• Form API #states
• Arbitrary JavaScript
• Drupal forms AJAX support, including:
  • ​​​Custom AJAX callbacks​
  • Custom AJAX commands
  • Autocomplete
  • How to safely change form values
  • Handling multiple related elements
  • Fallback when JavaScript isn't available
• Tabledrag and tableselect