run watch decorator after update completes

docs/getting-started/changelog.md

@@ -11,6 +11,7 @@ _During the beta period, these restrictions may be relaxed in the event of a mis
 - Fixed a bug in `sl-animation` where `sl-cancel` and `sl-finish` events would never fire
 - Fixed a bug where `sl-alert` wouldn't always transition properly
 - Fixed a bug where using `sl-menu` inside a shadow root would break keyboard selections [#382](https://github.com/shoelace-style/shoelace/issues/382)
+- Improved `@watch` decorator to run after update instead of during
 - Updated `sl-menu-item` checked icon to `check` instead of `check2`
 
 ## 2.0.0-beta.34

src/components/input/input.ts

@@ -257,8 +257,7 @@ export default class SlInput extends LitElement {
 
   @watch('value')
   handleValueChange() {
-    // Wait for the update to complete before checking the input's validity
-    this.updateComplete.then(() => (this.invalid = !this.input.checkValidity()));
+    this.invalid = !this.input.checkValidity();
   }
 
   render() {

src/components/textarea/textarea.ts

@@ -238,8 +238,7 @@ export default class SlTextarea extends LitElement {
 
   @watch('value')
   handleValueChange() {
-    // Wait for the update to complete before checking the input's validity
-    this.updateComplete.then(() => (this.invalid = !this.input.checkValidity()));
+    this.invalid = !this.input.checkValidity();
   }
 
   setTextareaHeight() {

src/internal/decorators.ts

@@ -63,8 +63,11 @@ export class EventEmitter<T> {
 
 // @watch decorator
 //
-// Runs when an observed property changes, e.g. @property or @internalProperty. This will only run after the first
-// update, so initial values will not trigger the watch function.
+// Runs after an observed property changes, e.g. @property or @internalProperty. This will only run after the first
+// update, so initial attribute => property mappings will not trigger the watch handler.
+//
+// Note that changing props in a watch handler *will* trigger a rerender. To make pre-update changes to observed
+// properties, use the `update()` method instead.
 //
 // Usage:
 //
@@ -74,15 +77,10 @@ export class EventEmitter<T> {
 //
 export function watch(propName: string) {
   return (protoOrDescriptor: any, name: string): any => {
-    const { firstUpdated, update } = protoOrDescriptor;
+    const { updated } = protoOrDescriptor;
 
-    protoOrDescriptor.firstUpdated = function (changedProps: Map<string, any>) {
-      firstUpdated.call(this, changedProps);
-      this.__didFirstUpdate = true;
-    };
-
-    protoOrDescriptor.update = function (changedProps: Map<string, any>) {
-      if (this.__didFirstUpdate && changedProps.has(propName)) {
+    protoOrDescriptor.updated = function (changedProps: Map<string, any>) {
+      if (this.__hasBeenUpdated && changedProps.has(propName)) {
         const oldValue = changedProps.get(propName);
         const newValue = this[propName];
 
@@ -91,7 +89,8 @@ export function watch(propName: string) {
         }
       }
 
-      update.call(this, changedProps);
+      updated.call(this, changedProps);
+      this.__hasBeenUpdated = true;
     };
   };
 }