refactor: Drop support for using propTypes to define observedAttrs (#125)

Author: rschristian

README.md

@@ -63,22 +63,6 @@ class Greeting extends Component {
 register(Greeting);
 ```
 
-If no `observedAttributes` are specified, they will be inferred from the keys of `propTypes` if present on the Component:
-
-```js
-// Other option: use PropTypes:
-function FullName({ first, last }) {
-  return <span>{first} {last}</span>
-}
-
-FullName.propTypes = {
-  first: Object,   // you can use PropTypes, or this
-  last: Object     // trick to define untyped props.
-};
-
-register(FullName, 'full-name');
-```
-
 ### Passing slots as props
 
 The `register()` function also accepts an optional fourth parameter, an options bag. At present, it allows you to opt-in to using shadow DOM for your custom element by setting the `shadow` property to `true`, and if so, you can also specify the encapsulation mode with `mode`, which can be either `'open'` or `'closed'`. Additionally, you may mark the shadow root as being serializable with the boolean `serializable` property.

src/index.js

@@ -40,10 +40,7 @@ export default function register(Component, tagName, propNames, options) {
 	/**
 	 * @type {string[]}
 	 */
-	propNames =
-		propNames ||
-		Component.observedAttributes ||
-		Object.keys(Component.propTypes || {});
+	propNames = propNames || Component.observedAttributes || [];
 	PreactElement.observedAttributes = propNames;
 
 	if (Component.formAssociated) {