• For <my-element foo={{bar}}> make sure foo is a notifying property! ➡️ notify: true

• Make sure you're using $= attribute binding! ➡️ <button data-index$=[[bar]]>

➡️ Make sure it's bubbling!

• this.dispatchEvent(new CustomEvent('meow', {bubbles: true, composed: true}));

➡️ Check your superclass methods!

• call super() if you're in the constructor
• and super.connectedCallback() for the connected callback
• and don't forget about the tricky super.ready() too! Or nothing will happen.

• twitter.com/polymer