vaadin · web-padawan · Jan 15, 2025 · Jan 15, 2025 · Jan 16, 2025 · Jan 16, 2025
diff --git a/dev/horizontal-layout.html b/dev/horizontal-layout.html
@@ -0,0 +1,74 @@
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="UTF-8" />
+    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <title>Horizontal layout</title>
+    <script type="module" src="./common.js"></script>
+
+    <script type="module">
+      import '@vaadin/horizontal-layout';
+    </script>
+  </head>
+
+  <body>
+    <vaadin-horizontal-layout style="border: solid 1px blue; width: 600px;" theme="spacing wrap">
+      <div style="background: #90ee90; width: 100px">Start</div>
+      <div style="background: #90ee90; width: 100px">Start</div>
+      <div slot="middle" style="background: #ffd700;">Middle</div>
+      <div slot="end" style="background: #f08080; width: 100px">End</div>
+    </vaadin-horizontal-layout>
+
+    <br />
+
+    <vaadin-horizontal-layout style="border: solid 1px blue; width: 350px;" theme="spacing wrap">
+      <div style="background: #90ee90; width: 100px">Start</div>
+      <div style="background: #90ee90; width: 100px">Start</div>
+      <div slot="middle" style="background: #ffd700;">Middle</div>
+      <div slot="end" style="background: #f08080; width: 100px">End</div>
+    </vaadin-horizontal-layout>
+
+    <br />
+
+    <vaadin-horizontal-layout style="border: solid 1px blue; width: 350px;" theme="spacing wrap">
+      <div style="background: #90ee90; width: 200px">Start</div>
+      <div style="background: #90ee90; width: 100px">Start</div>
+      <div slot="middle" style="background: #ffd700;">Middle</div>
+      <div slot="end" style="background: #f08080; width: 100px">End</div>
+    </vaadin-horizontal-layout>
+
+    <br />
+
+    <vaadin-horizontal-layout style="border: solid 1px blue; width: 400px;" theme="spacing wrap">
+      <div style="background: #90ee90; width: 100px">Start</div>
+      <div style="background: #90ee90; width: 100px">Start</div>
+      <div slot="middle" style="background: #ffd700;">Middle</div>
+    </vaadin-horizontal-layout>
+
+    <br />
+
+    <vaadin-horizontal-layout style="border: solid 1px blue; width: 250px;" theme="spacing wrap">
+      <div style="background: #90ee90; width: 100px">Start</div>
+      <div style="background: #90ee90; width: 100px">Start</div>
+      <div slot="middle" style="background: #ffd700;">Middle</div>
+    </vaadin-horizontal-layout>
+
+
+    <br />
+
+    <vaadin-horizontal-layout style="border: solid 1px blue; width: 400px;" theme="spacing wrap">
+      <div slot="middle" style="background: #ffd700;">Middle</div>
+      <div slot="end" style="background: #f08080; width: 100px">End</div>
+      <div slot="end" style="background: #f08080; width: 100px">End</div>
+    </vaadin-horizontal-layout>
+
+    <br />
+
+    <vaadin-horizontal-layout style="border: solid 1px blue; width: 250px;" theme="spacing wrap">
+      <div slot="middle" style="background: #ffd700;">Middle</div>
+      <div slot="end" style="background: #f08080; width: 100px">End</div>
+      <div slot="end" style="background: #f08080; width: 100px">End</div>
+    </vaadin-horizontal-layout>
+  </body>
+</html>
diff --git a/packages/horizontal-layout/src/vaadin-horizontal-layout-mixin.d.ts b/packages/horizontal-layout/src/vaadin-horizontal-layout-mixin.d.ts
@@ -0,0 +1,11 @@
+/**
+ * @license
+ * Copyright (c) 2017 - 2025 Vaadin Ltd.
+ * This program is available under Apache License Version 2.0, available at https://vaadin.com/license/
+ */
+import type { Constructor } from '@open-wc/dedupe-mixin';
+import type { ResizeMixinClass } from '@vaadin/component-base/src/resize-mixin.js';
+
+export declare function HorizontalLayoutMixin<T extends Constructor<HTMLElement>>(
+  base: T,
+): Constructor<ResizeMixinClass> & T;
diff --git a/packages/horizontal-layout/src/vaadin-horizontal-layout-mixin.js b/packages/horizontal-layout/src/vaadin-horizontal-layout-mixin.js
@@ -0,0 +1,117 @@
+/**
+ * @license
+ * Copyright (c) 2017 - 2025 Vaadin Ltd.
+ * This program is available under Apache License Version 2.0, available at https://vaadin.com/license/
+ */
+import { isEmptyTextNode } from '@vaadin/component-base/src/dom-utils.js';
+import { ResizeMixin } from '@vaadin/component-base/src/resize-mixin.js';
+import { SlotObserver } from '@vaadin/component-base/src/slot-observer.js';
+
+/**
+ * @polymerMixin
+ * @mixes ResizeMixin
+ */
+export const HorizontalLayoutMixin = (superClass) =>
+  class extends ResizeMixin(superClass) {
+    /** @protected */
+    ready() {
+      super.ready();
+
+      const startSlot = this.shadowRoot.querySelector('slot:not([name])');
+      this.__startSlotObserver = new SlotObserver(startSlot, ({ currentNodes, removedNodes }) => {
+        if (removedNodes.length) {
+          this.__clearAttribute(removedNodes, 'last-start-child');
+          this.__clearAttribute(removedNodes, 'first-in-row');
+        }
+
+        const children = currentNodes.filter((node) => node.nodeType === Node.ELEMENT_NODE);
+        this.__updateAttributes(children, 'start', false, true);
+
+        const nodes = currentNodes.filter((node) => !isEmptyTextNode(node));
+        this.toggleAttribute('has-start', nodes.length > 0);
+
+        this.__updateRowState();
+      });
+
+      const endSlot = this.shadowRoot.querySelector('[name="end"]');
+      this.__endSlotObserver = new SlotObserver(endSlot, ({ currentNodes, removedNodes }) => {
+        if (removedNodes.length) {
+          this.__clearAttribute(removedNodes, 'first-end-child');
+          this.__clearAttribute(removedNodes, 'first-in-row');
+        }
+
+        this.__updateAttributes(currentNodes, 'end', true, false);
+
+        this.toggleAttribute('has-end', currentNodes.length > 0);
+
+        this.__updateRowState();
+      });
+
+      const middleSlot = this.shadowRoot.querySelector('[name="middle"]');
+      this.__middleSlotObserver = new SlotObserver(middleSlot, ({ currentNodes, removedNodes }) => {
+        if (removedNodes.length) {
+          this.__clearAttribute(removedNodes, 'first-middle-child');
+          this.__clearAttribute(removedNodes, 'last-middle-child');
+          this.__clearAttribute(removedNodes, 'first-in-row');
+        }
+
+        this.__updateAttributes(currentNodes, 'middle', true, true);
+
+        this.toggleAttribute('has-middle', currentNodes.length > 0);
+
+        this.__updateRowState();
+      });
+    }
+
+    /**
+     * @protected
+     * @override
+     */
+    _onResize() {
+      this.__updateRowState();
+    }
+
+    /** @private */
+    __clearAttribute(nodes, attr) {
+      const el = nodes.find((node) => node.nodeType === Node.ELEMENT_NODE && node.hasAttribute(attr));
+      if (el) {
+        el.removeAttribute(attr);
+      }
+    }
+
+    /** @private */
+    __updateAttributes(nodes, slot, setFirst, setLast) {
+      nodes.forEach((child, idx) => {
+        if (setFirst) {
+          const attr = `first-${slot}-child`;
+          if (idx === 0) {
+            child.setAttribute(attr, '');
+          } else if (child.hasAttribute(attr)) {
+            child.removeAttribute(attr);
+          }
+        }
+
+        if (setLast) {
+          const attr = `last-${slot}-child`;
+          if (idx === nodes.length - 1) {
+            child.setAttribute(attr, '');
+          } else if (child.hasAttribute(attr)) {
+            child.removeAttribute(attr);
+          }
+        }
+      });
+    }
+
+    /** @private */
+    __updateRowState() {
+      let offset = 0;
+      for (const child of this.children) {
+        if (child.offsetTop > offset) {
+          offset = child.offsetTop;
+          child.setAttribute('first-in-row', '');
+        } else {
+          child.removeAttribute('first-in-row');
+        }
+      }
+    }
+  };
diff --git a/packages/horizontal-layout/src/vaadin-horizontal-layout-styles.js b/packages/horizontal-layout/src/vaadin-horizontal-layout-styles.js
@@ -27,4 +27,24 @@ export const horizontalLayoutStyles = css`
   :host([theme~='spacing']) {
     gap: 1em;
   }
+
+  :host([has-end]:not([has-middle])) ::slotted([last-start-child]) {
+    margin-inline-end: auto;
+  }
+
+  ::slotted([first-middle-child]) {
+    margin-inline-start: auto;
+  }
+
+  ::slotted([last-middle-child]) {
+    margin-inline-end: auto;
+  }
+
+  :host([has-start]:not([has-middle])) ::slotted([first-end-child]) {
+    margin-inline-start: auto;
+  }
+
+  ::slotted([slot='end'][first-in-row]) {
+    margin-inline-start: auto;
+  }
 `;
diff --git a/packages/horizontal-layout/src/vaadin-horizontal-layout.d.ts b/packages/horizontal-layout/src/vaadin-horizontal-layout.d.ts
@@ -5,6 +5,7 @@
  */
 import { ElementMixin } from '@vaadin/component-base/src/element-mixin.js';
 import { ThemableMixin } from '@vaadin/vaadin-themable-mixin/vaadin-themable-mixin.js';
+import { HorizontalLayoutMixin } from './vaadin-horizontal-layout-mixin.js';
 
 /**
  * `<vaadin-horizontal-layout>` provides a simple way to horizontally align your HTML elements.
@@ -26,8 +27,18 @@ import { ThemableMixin } from '@vaadin/vaadin-themable-mixin/vaadin-themable-mix
  * `theme="padding"` | Applies the default amount of CSS padding for the host element (specified by the theme)
  * `theme="spacing"` | Applies the default amount of CSS margin between items (specified by the theme)
  * `theme="wrap"` | Items wrap to the next row when they exceed the layout width
+ *
+ * ### Component's slots
+ *
+ * The following slots are available to be set:
+ *
+ * Slot name          | Description
+ * -------------------|---------------
+ * no name            | Default slot
+ * `middle`           | Slot for the content placed in the middle
+ * `end`              | Slot for the content placed at the end
  */
-declare class HorizontalLayout extends ThemableMixin(ElementMixin(HTMLElement)) {}
+declare class HorizontalLayout extends HorizontalLayoutMixin(ThemableMixin(ElementMixin(HTMLElement))) {}
 
 declare global {
   interface HTMLElementTagNameMap {

diff --git a/packages/horizontal-layout/src/vaadin-horizontal-layout.js b/packages/horizontal-layout/src/vaadin-horizontal-layout.js
@@ -7,6 +7,7 @@ import { html, PolymerElement } from '@polymer/polymer/polymer-element.js';
 import { defineCustomElement } from '@vaadin/component-base/src/define.js';
 import { ElementMixin } from '@vaadin/component-base/src/element-mixin.js';
 import { registerStyles, ThemableMixin } from '@vaadin/vaadin-themable-mixin/vaadin-themable-mixin.js';
+import { HorizontalLayoutMixin } from './vaadin-horizontal-layout-mixin.js';
 import { horizontalLayoutStyles } from './vaadin-horizontal-layout-styles.js';
 
 registerStyles('vaadin-horizontal-layout', horizontalLayoutStyles, { moduleId: 'vaadin-horizontal-layout-styles' });
@@ -32,14 +33,29 @@ registerStyles('vaadin-horizontal-layout', horizontalLayoutStyles, { moduleId: '
  * `theme="spacing"` | Applies the default amount of CSS margin between items (specified by the theme)
  * `theme="wrap"` | Items wrap to the next row when they exceed the layout width
  *
+ * ### Component's slots
+ *
+ * The following slots are available to be set:
+ *
+ * Slot name          | Description
+ * -------------------|---------------
+ * no name            | Default slot
+ * `middle`           | Slot for the content placed in the middle
+ * `end`              | Slot for the content placed at the end
+ *
  * @customElement
  * @extends HTMLElement
  * @mixes ThemableMixin
  * @mixes ElementMixin
+ * @mixes HorizontalLayoutMixin
  */
-class HorizontalLayout extends ElementMixin(ThemableMixin(PolymerElement)) {
+class HorizontalLayout extends HorizontalLayoutMixin(ElementMixin(ThemableMixin(PolymerElement))) {
   static get template() {
-    return html`<slot></slot>`;
+    return html`
+      <slot></slot>
+      <slot name="middle"></slot>
+      <slot name="end"></slot>
+    `;
   }
 
   static get is() {

diff --git a/packages/horizontal-layout/src/vaadin-lit-horizontal-layout.js b/packages/horizontal-layout/src/vaadin-lit-horizontal-layout.js
@@ -8,6 +8,7 @@ import { defineCustomElement } from '@vaadin/component-base/src/define.js';
 import { ElementMixin } from '@vaadin/component-base/src/element-mixin.js';
 import { PolylitMixin } from '@vaadin/component-base/src/polylit-mixin.js';
 import { ThemableMixin } from '@vaadin/vaadin-themable-mixin/vaadin-themable-mixin.js';
+import { HorizontalLayoutMixin } from './vaadin-horizontal-layout-mixin.js';
 import { horizontalLayoutStyles } from './vaadin-horizontal-layout-styles.js';
 
 /**
@@ -19,7 +20,7 @@ import { horizontalLayoutStyles } from './vaadin-horizontal-layout-styles.js';
  * There is no ETA regarding specific Vaadin version where it'll land.
  * Feel free to try this code in your apps as per Apache 2.0 license.
  */
-class HorizontalLayout extends ThemableMixin(ElementMixin(PolylitMixin(LitElement))) {
+class HorizontalLayout extends HorizontalLayoutMixin(ThemableMixin(ElementMixin(PolylitMixin(LitElement)))) {
   static get is() {
     return 'vaadin-horizontal-layout';
   }
@@ -30,7 +31,11 @@ class HorizontalLayout extends ThemableMixin(ElementMixin(PolylitMixin(LitElemen
 
   /** @protected */
   render() {
-    return html`<slot></slot>`;
+    return html`
+      <slot></slot>
+      <slot name="middle"></slot>
+      <slot name="end"></slot>
+    `;
   }
 }