feat: add itemClassNameGenerator to generate CSS class names

packages/combo-box/src/vaadin-combo-box-mixin.d.ts

@@ -64,6 +64,14 @@ export declare class ComboBoxMixinClass<TItem> {
    */
   items: TItem[] | undefined;
 
+  /**
+   * A function used to generate CSS class names for dropdown
+   * items based on the item. The return value should be the
+   * generated class name as a string, or multiple class names
+   * separated by whitespace characters.
+   */
+  itemClassNameGenerator: (item: TItem) => string;
+
   /**
    * If `true`, the user can input a value that is not present in the items list.
    * `value` property will be set to the input value in this case.

packages/combo-box/src/vaadin-combo-box-mixin.js

@@ -196,6 +196,16 @@ export const ComboBoxMixin = (subclass) =>
           sync: true,
         },
 
+        /**
+         * A function used to generate CSS class names for dropdown
+         * items based on the item. The return value should be the
+         * generated class name as a string, or multiple class names
+         * separated by whitespace characters.
+         */
+        itemClassNameGenerator: {
+          type: Object,
+        },
+
         /**
          * Path for label of the item. If `items` is an array of objects, the
          * `itemLabelPath` is used to fetch the displayed string label for each
@@ -287,7 +297,7 @@ export const ComboBoxMixin = (subclass) =>
       return [
         '_selectedItemChanged(selectedItem, itemValuePath, itemLabelPath)',
         '_openedOrItemsChanged(opened, _dropdownItems, loading, __keepOverlayOpened)',
-        '_updateScroller(_scroller, _dropdownItems, opened, loading, selectedItem, itemIdPath, _focusedIndex, renderer, _theme)',
+        '_updateScroller(_scroller, _dropdownItems, opened, loading, selectedItem, itemIdPath, _focusedIndex, renderer, _theme, itemClassNameGenerator)',
       ];
     }
 
@@ -503,7 +513,18 @@ export const ComboBoxMixin = (subclass) =>
 
     /** @private */
     // eslint-disable-next-line max-params
-    _updateScroller(scroller, items, opened, loading, selectedItem, itemIdPath, focusedIndex, renderer, theme) {
+    _updateScroller(
+      scroller,
+      items,
+      opened,
+      loading,
+      selectedItem,
+      itemIdPath,
+      focusedIndex,
+      renderer,
+      theme,
+      itemClassNameGenerator,
+    ) {
       if (scroller) {
         if (opened) {
           scroller.style.maxHeight =
@@ -519,6 +540,7 @@ export const ComboBoxMixin = (subclass) =>
           focusedIndex,
           renderer,
           theme,
+          itemClassNameGenerator,
         });
 
         // NOTE: in PolylitMixin, setProperties() waits for `hasUpdated` to be set.

packages/combo-box/src/vaadin-combo-box-scroller-mixin.js

@@ -63,6 +63,17 @@ export const ComboBoxScrollerMixin = (superClass) =>
           observer: '__selectedItemChanged',
         },
 
+        /**
+         * A function used to generate CSS class names for dropdown
+         * items based on the item. The return value should be the
+         * generated class name as a string, or multiple class names
+         * separated by whitespace characters.
+         */
+        itemClassNameGenerator: {
+          type: Object,
+          observer: '__itemClassNameGeneratorChanged',
+        },
+
         /**
          * Path for the id of the item, used to detect whether the item is selected.
          */
@@ -254,6 +265,13 @@ export const ComboBoxScrollerMixin = (superClass) =>
       this.requestContentUpdate();
     }
 
+    /** @private */
+    __itemClassNameGeneratorChanged(generator, oldGenerator) {
+      if (generator || oldGenerator) {
+        this.requestContentUpdate();
+      }
+    }
+
     /** @private */
     __focusedIndexChanged(index, oldIndex) {
       if (index !== oldIndex) {
@@ -305,6 +323,12 @@ export const ComboBoxScrollerMixin = (superClass) =>
         focused: !this.loading && focusedIndex === index,
       });
 
+      if (typeof this.itemClassNameGenerator === 'function') {
+        el.className = this.itemClassNameGenerator(item);
+      } else if (el.className !== '') {
+        el.className = '';
+      }
+
       // NOTE: in PolylitMixin, setProperties() waits for `hasUpdated` to be set.
       // However, this causes issues with virtualizer. So we enforce sync update.
       if (el.performUpdate && !el.hasUpdated) {

packages/combo-box/test/item-class-name-generator-lit.test.js

@@ -0,0 +1,3 @@
+import './not-animated-styles.js';
+import '../theme/lumo/vaadin-lit-combo-box.js';
+import './item-class-name-generator.common.js';

packages/combo-box/test/item-class-name-generator-polymer.test.js

@@ -0,0 +1,3 @@
+import './not-animated-styles.js';
+import '../vaadin-combo-box.js';
+import './item-class-name-generator.common.js';

packages/combo-box/test/item-class-name-generator.common.js

@@ -0,0 +1,57 @@
+import { expect } from '@esm-bundle/chai';
+import { fixtureSync, nextRender } from '@vaadin/testing-helpers';
+import { getAllItems } from './helpers.js';
+
+describe('itemClassNameGenerator', () => {
+  let comboBox;
+
+  beforeEach(async () => {
+    comboBox = fixtureSync('<vaadin-combo-box></vaadin-combo-box>');
+    await nextRender();
+    comboBox.items = ['foo', 'bar', 'baz'];
+  });
+
+  it('should set class name on dropdown items', async () => {
+    comboBox.itemClassNameGenerator = (item) => `item-${item}`;
+    comboBox.open();
+    await nextRender();
+    const items = getAllItems(comboBox);
+    expect(items[0].className).to.equal('item-foo');
+    expect(items[1].className).to.equal('item-bar');
+    expect(items[2].className).to.equal('item-baz');
+  });
+
+  it('should remove class name when return value is empty string', async () => {
+    comboBox.itemClassNameGenerator = (item) => `item-${item}`;
+    comboBox.open();
+    await nextRender();
+
+    comboBox.close();
+    comboBox.itemClassNameGenerator = () => '';
+
+    comboBox.open();
+    await nextRender();
+
+    const items = getAllItems(comboBox);
+    expect(items[0].className).to.equal('');
+    expect(items[1].className).to.equal('');
+    expect(items[2].className).to.equal('');
+  });
+
+  it('should remove class name when generator is set to null', async () => {
+    comboBox.itemClassNameGenerator = (item) => `item-${item}`;
+    comboBox.open();
+    await nextRender();
+
+    comboBox.close();
+    comboBox.itemClassNameGenerator = null;
+
+    comboBox.open();
+    await nextRender();
+
+    const items = getAllItems(comboBox);
+    expect(items[0].className).to.equal('');
+    expect(items[1].className).to.equal('');
+    expect(items[2].className).to.equal('');
+  });
+});

packages/combo-box/test/typings/combo-box.types.ts

@@ -111,6 +111,7 @@ assertType<boolean>(narrowedComboBox.opened);
 assertType<string>(narrowedComboBox.filter);
 assertType<TestComboBoxItem[] | undefined>(narrowedComboBox.filteredItems);
 assertType<TestComboBoxItem[] | undefined>(narrowedComboBox.items);
+assertType<(item: TestComboBoxItem) => string>(narrowedComboBox.itemClassNameGenerator);
 assertType<string | null | undefined>(narrowedComboBox.itemIdPath);
 assertType<string>(narrowedComboBox.itemLabelPath);
 assertType<string>(narrowedComboBox.itemValuePath);

packages/multi-select-combo-box/src/vaadin-multi-select-combo-box.d.ts

@@ -231,6 +231,14 @@ declare class MultiSelectComboBox<TItem = ComboBoxDefaultItem> extends HTMLEleme
    */
   items: TItem[] | undefined;
 
+  /**
+   * A function used to generate CSS class names for dropdown
+   * items and selected chips based on the item. The return
+   * value should be the generated class name as a string, or
+   * multiple class names separated by whitespace characters.
+   */
+  itemClassNameGenerator: (item: TItem) => string;
+
   /**
    * The item property used for a visual representation of the item.
    * @attr {string} item-label-path

packages/multi-select-combo-box/src/vaadin-multi-select-combo-box.js

@@ -180,6 +180,7 @@ class MultiSelectComboBox extends ResizeMixin(InputControlMixin(ThemableMixin(El
           filtered-items="[[filteredItems]]"
           selected-items="[[selectedItems]]"
           selected-items-on-top="[[selectedItemsOnTop]]"
+          item-class-name-generator="[[itemClassNameGenerator]]"
           top-group="[[_topGroup]]"
           opened="{{opened}}"
           renderer="[[renderer]]"
@@ -279,6 +280,17 @@ class MultiSelectComboBox extends ResizeMixin(InputControlMixin(ThemableMixin(El
         type: Array,
       },
 
+      /**
+       * A function used to generate CSS class names for dropdown
+       * items and selected chips based on the item. The return
+       * value should be the generated class name as a string, or
+       * multiple class names separated by whitespace characters.
+       */
+      itemClassNameGenerator: {
+        type: Object,
+        observer: '__itemClassNameGeneratorChanged',
+      },
+
       /**
        * The item property used for a visual representation of the item.
        * @attr {string} item-label-path
@@ -761,6 +773,13 @@ class MultiSelectComboBox extends ResizeMixin(InputControlMixin(ThemableMixin(El
     }
   }
 
+  /** @private */
+  __itemClassNameGeneratorChanged(generator, oldGenerator) {
+    if (generator || oldGenerator) {
+      this.__updateChips();
+    }
+  }
+
   /** @private */
   _pageSizeChanged(pageSize, oldPageSize) {
     if (Math.floor(pageSize) !== pageSize || pageSize <= 0) {
@@ -934,6 +953,10 @@ class MultiSelectComboBox extends ResizeMixin(InputControlMixin(ThemableMixin(El
     chip.label = label;
     chip.setAttribute('title', label);
 
+    if (typeof this.itemClassNameGenerator === 'function') {
+      chip.className = this.itemClassNameGenerator(item);
+    }
+
     chip.addEventListener('item-removed', (e) => this._onItemRemoved(e));
     chip.addEventListener('mousedown', (e) => this._preventBlur(e));
 

packages/multi-select-combo-box/test/basic.test.js

@@ -128,6 +128,12 @@ describe('basic', () => {
       expect(comboBox.hasAttribute('loading')).to.be.false;
     });
 
+    it('should propagate itemClassNameGenerator property to combo-box', () => {
+      const generator = (item) => item;
+      comboBox.itemClassNameGenerator = generator;
+      expect(internal.itemClassNameGenerator).to.equal(generator);
+    });
+
     it('should update filteredItems when combo-box filteredItems changes', () => {
       internal.filteredItems = ['apple'];
       expect(comboBox.filteredItems).to.deep.equal(['apple']);

packages/multi-select-combo-box/test/chips.test.js

@@ -553,4 +553,58 @@ describe('chips', () => {
       expect(overlayPart.clientWidth).to.be.equal(comboBox.clientWidth);
     });
   });
+
+  describe('itemClassNameGenerator', () => {
+    beforeEach(() => {
+      comboBox.autoExpandHorizontally = true;
+    });
+
+    it('should set class name on the selected item chips', async () => {
+      comboBox.itemClassNameGenerator = (item) => item;
+      comboBox.selectedItems = ['apple', 'lemon'];
+      await nextRender();
+
+      const chips = getChips(comboBox);
+      expect(chips[1].className).to.equal('apple');
+      expect(chips[2].className).to.equal('lemon');
+    });
+
+    it('should set class name when generator set after selecting', async () => {
+      comboBox.selectedItems = ['apple', 'lemon'];
+      await nextRender();
+
+      comboBox.itemClassNameGenerator = (item) => item;
+      await nextRender();
+
+      const chips = getChips(comboBox);
+      expect(chips[1].className).to.equal('apple');
+      expect(chips[2].className).to.equal('lemon');
+    });
+
+    it('should remove class name when generator returns empty string', async () => {
+      comboBox.itemClassNameGenerator = (item) => item;
+      comboBox.selectedItems = ['apple', 'lemon'];
+      await nextRender();
+
+      comboBox.itemClassNameGenerator = () => '';
+      await nextRender();
+
+      const chips = getChips(comboBox);
+      expect(chips[1].className).to.equal('');
+      expect(chips[2].className).to.equal('');
+    });
+
+    it('should remove class name when generator is set to null', async () => {
+      comboBox.itemClassNameGenerator = (item) => item;
+      comboBox.selectedItems = ['apple', 'lemon'];
+      await nextRender();
+
+      comboBox.itemClassNameGenerator = null;
+      await nextRender();
+
+      const chips = getChips(comboBox);
+      expect(chips[1].className).to.equal('');
+      expect(chips[2].className).to.equal('');
+    });
+  });
 });

packages/multi-select-combo-box/test/typings/multi-select-combo-box.types.ts

@@ -88,6 +88,7 @@ assertType<boolean | null | undefined>(narrowedComboBox.autoOpenDisabled);
 assertType<string>(narrowedComboBox.filter);
 assertType<TestComboBoxItem[] | undefined>(narrowedComboBox.filteredItems);
 assertType<TestComboBoxItem[] | undefined>(narrowedComboBox.items);
+assertType<(item: TestComboBoxItem) => string>(narrowedComboBox.itemClassNameGenerator);
 assertType<string | null | undefined>(narrowedComboBox.itemIdPath);
 assertType<string>(narrowedComboBox.itemLabelPath);
 assertType<string>(narrowedComboBox.itemValuePath);