fix(sbb-form-field): update floating label on programmatic changes

src/elements/form-field/form-field/form-field.spec.ts

@@ -416,7 +416,7 @@ describe(`sbb-form-field`, () => {
       expect(element).to.have.attribute('data-input-empty');
     });
 
-    it('should reset floating label when calling reset of sbb-form-field', async () => {
+    it('should reset floating label when changing value programmatically', async () => {
       const element: SbbFormFieldElement = await fixture(html`
         <sbb-form-field floating-label>
           <input />
@@ -433,15 +433,58 @@ describe(`sbb-form-field`, () => {
       input.value = '';
       await waitForLitRender(element);
 
-      // Then empty state is not updated
-      expect(element).not.to.have.attribute('data-input-empty');
+      // Then the empty state is updated
+      expect(element).to.have.attribute('data-input-empty');
+    });
+
+    it('should unpatch on input removal', async () => {
+      const element: SbbFormFieldElement = await fixture(html`
+        <sbb-form-field floating-label></sbb-form-field>
+      `);
+
+      const newInput = document.createElement('input');
 
-      // When manually calling reset method
-      element.reset();
+      const originalSetter = Object.getOwnPropertyDescriptor(
+        Object.getPrototypeOf(newInput),
+        'value',
+      )!.set;
+
+      element.appendChild(newInput);
       await waitForLitRender(element);
 
-      // Then empty state should be updated
-      expect(element).to.have.attribute('data-input-empty');
+      expect(Object.getOwnPropertyDescriptor(newInput, 'value')!.set).not.to.be.equal(
+        originalSetter,
+      );
+
+      newInput.remove();
+      await waitForLitRender(element);
+
+      expect(Object.getOwnPropertyDescriptor(newInput, 'value')!.set).to.be.equal(originalSetter);
+    });
+
+    it('should unpatch on disconnection', async () => {
+      const element: SbbFormFieldElement = await fixture(html`
+        <sbb-form-field floating-label></sbb-form-field>
+      `);
+
+      const newInput = document.createElement('input');
+
+      const originalSetter = Object.getOwnPropertyDescriptor(
+        Object.getPrototypeOf(newInput),
+        'value',
+      )!.set;
+
+      element.appendChild(newInput);
+      await waitForLitRender(element);
+
+      expect(Object.getOwnPropertyDescriptor(newInput, 'value')!.set).not.to.be.equal(
+        originalSetter,
+      );
+
+      element.remove();
+      await waitForLitRender(element);
+
+      expect(Object.getOwnPropertyDescriptor(newInput, 'value')!.set).to.be.equal(originalSetter);
     });
   });
 });

src/elements/form-field/form-field/form-field.ts

@@ -20,6 +20,8 @@
 
 const supportedPopupTagNames = ['sbb-autocomplete', 'sbb-autocomplete-grid', 'sbb-select'];
 
+const patchedInputs = new WeakMap<HTMLInputElement, PropertyDescriptor>();
+
 /**
  * It wraps an input element adding label, errors, icon, etc.
  *
@@ -155,6 +157,9 @@
     super.disconnectedCallback();
     this._formFieldAttributeObserver?.disconnect();
     this._inputAbortController.abort();
+    if (this._input?.localName === 'input') {
+      this._unpatchInputValue();
+    }
   }
 
   private _onPopupOpen({ target }: CustomEvent<void>): void {
@@ -207,11 +212,17 @@
    * It is used internally to assign the attributes of `<input>` to `_id` and `_input` and to observe the native readonly and disabled attributes.
    */
   private _onSlotInputChange(event: Event): void {
-    this._input = (event.target as HTMLSlotElement)
+    const newInput = (event.target as HTMLSlotElement)
       .assignedElements()
       .find((e): e is HTMLElement => this._supportedInputElements.includes(e.localName));
     this._assignSlots();
 
+    if (this._input && this._input.localName === 'input' && newInput !== this._input) {
+      this._unpatchInputValue();
+    }
+
+    this._input = newInput;
+
     if (!this._input) {
       return;
     }
@@ -285,7 +296,9 @@
 
     let inputFocusElement = this._input;
 
-    if (this._input.localName === 'sbb-select') {
+    if (this._input.localName === 'input') {
+      this._patchInputValue();
+    } else if (this._input.localName === 'sbb-select') {
       this._input.addEventListener('stateChange', () => this._checkAndUpdateInputEmpty(), {
         signal: this._inputAbortController.signal,
       });
@@ -337,6 +350,45 @@
     return this._input?.closest('form');
   }
 
+  // We need to patch the value property of the HTMLInputElement in order
+  // to be able to reset the floating label in the empty state.
+  private _patchInputValue(): void {
+    const inputElement = this._input as HTMLInputElement;
+    const originalDescriptor = Object.getOwnPropertyDescriptor(
+      Object.getPrototypeOf(inputElement),
+      'value',
+    );
+
+    if (!originalDescriptor || !originalDescriptor.set || !originalDescriptor.get) {
+      return;
+    }
+
+    patchedInputs.set(inputElement, originalDescriptor);
+
+    const { get: getter, set: setter } = originalDescriptor;
+    const checkAndUpdateInputEmpty = (): void => this._checkAndUpdateInputEmpty();
+
+    Object.defineProperty(inputElement, 'value', {
+      ...originalDescriptor,
+      get() {
+        return getter.call(this);
+      },
+      set(newValue) {
+        setter.call(this, newValue);
+        checkAndUpdateInputEmpty();
+      },
+    });
+  }
+
+  private _unpatchInputValue(): void {
+    const inputElement = this._input as HTMLInputElement;
+    const originalDescriptor = patchedInputs.get(inputElement);
+    if (originalDescriptor) {
+      Object.defineProperty(inputElement, 'value', originalDescriptor);
+      patchedInputs.delete(inputElement);
+    }
+  }
+
   private _checkAndUpdateInputEmpty(): void {
     this.toggleAttribute(
       'data-input-empty',